Electronic powder dispenser
- Thread starter old keeper
- Start date
Most inexpensive electronic scales are strain gauge scales. Treat them accordingly, and understand their weaknesses.
Electronic scales are good for:
1. Speed
2. Less attention (can be seating bullets as the next charge is being dropped)
3. Decent accuracy (plenty enough for hunting loads).
What they (inexpensive electronic scales) typically are not, is:
1. Exceedingly accurate (usually within .2's of a grain, which is what most beam scales are expected to meet)
2. Resistant to drifting (dirty power, fluorescent lights, A/C drafts etc.)
Beam scales (quality ones) are typically more accurate (+/- .1 of a grain) than cheap electronic scales (sub $500), but take more time and attention.
Cheap electronic scales speed things up, but typically are not as accurate as people think, and don't really show it until you put your ammo across a doppler radar. Again, the ammo produced is more than adequate for hunting purposes, but at long range it becomes pretty obvious that the scales drift...a lot. I compared loads dropped from an RCBS Chargemaster with a FX-120, and it's really not an argument that they drift.
The high end scales like Sartorius, Fx's, etc. are lab grade, magnetic resistance scales. As such they are stupidly accurate (+/- .02 of a grain), but have a hefty price tag. And are unaffected by temperature change, power fluctuations, and are typically shielded from air/draft disturbance.
Inexpensive powder dispenser scales have their place, as most have no need for uber accurate powder charges (and often have other contributing factors that degrade their ammo quality; neck tension, brass uniformity, primer ignition). So don't take my little epistle as a negative/pejorative of them; rather just explaining the differences, so that people can make an informed decision when they buy, or, talk crap about how good their "X" solution works.
Electronic scales are good for:
1. Speed
2. Less attention (can be seating bullets as the next charge is being dropped)
3. Decent accuracy (plenty enough for hunting loads).
What they (inexpensive electronic scales) typically are not, is:
1. Exceedingly accurate (usually within .2's of a grain, which is what most beam scales are expected to meet)
2. Resistant to drifting (dirty power, fluorescent lights, A/C drafts etc.)
Beam scales (quality ones) are typically more accurate (+/- .1 of a grain) than cheap electronic scales (sub $500), but take more time and attention.
Cheap electronic scales speed things up, but typically are not as accurate as people think, and don't really show it until you put your ammo across a doppler radar. Again, the ammo produced is more than adequate for hunting purposes, but at long range it becomes pretty obvious that the scales drift...a lot. I compared loads dropped from an RCBS Chargemaster with a FX-120, and it's really not an argument that they drift.
The high end scales like Sartorius, Fx's, etc. are lab grade, magnetic resistance scales. As such they are stupidly accurate (+/- .02 of a grain), but have a hefty price tag. And are unaffected by temperature change, power fluctuations, and are typically shielded from air/draft disturbance.
Inexpensive powder dispenser scales have their place, as most have no need for uber accurate powder charges (and often have other contributing factors that degrade their ammo quality; neck tension, brass uniformity, primer ignition). So don't take my little epistle as a negative/pejorative of them; rather just explaining the differences, so that people can make an informed decision when they buy, or, talk crap about how good their "X" solution works.
Electronic scales, (not the automatic powder dispensers, just the scales) can be a very useful tool for precision reloading. Even some ridiculously inexpensive ones, if you get lucky. I have, several times. £15 for one, £25 for another. £12 for one that was no good.
The trouble is with the sort that only resolve to say 1/10 grain. Straight away you are stuck with something that can only display within a 0.2 grain window. That's before base accuracy, calibration state, warmup drift etc. I don't think that's quite good enough.
My two resolve to 1 milligram, and have a two-weight calibration routine, which is supposed to linearize the reading between the low and the high mass cal. weights, that came with them. 1 milligram is about 0.015 grains. When switched to display in grains they work in increments of 0.02 grains, according to the rounding method used internally. Natively they work in milligrams, which is how I mostly use them, just because I prefer to, and maybe have that extra edge..
I see on the LCD display a readout that could be 0.02 grains high, or low, or somewhere in-between. Plus the other errors. Not to kid myself, I still reckon they are accurate, and precise enough, to measure powder to within 0.1 grains total variation, absolute. Which is good enough for me. They will also move with just one or two kernels of stick powder, which is interesting, but I'm not one to worry about individual kernels.
They have been tested with extremely precise laboratory standard test weights, and proved to be good. As have, surprisingly, the calibration weights supplied with them..
I have two, in case one goes bad. No other reason, and it's not happened yet.
I like them, know how to check the calibration which rarely drifts after a bit of use (maybe those strain gauges settle down after a while) and use them in a "temperature controlled environment" i.e. inside my house. They run off batteries, not plugged into the mains. I don't have any striplights, which certainly can cause EMI, which I can detect through my hearing aids on the telecoil setting. Quite interesting having a "super sense" to be able to hear EMI at audible frequencies.
So, I throw an undercharge into the pan (a Lyman one with a built in funnel). Using a basic Lee Perfect Powder Measure that I've had for many years. Or even just a Lee dipper if I don't want to fill up the powder thrower.. Put on the scale and manually trickle up (RCBS trickler) Only takes a few seconds. I know what my pan weighs, so every time I lift it off the scale I observe the negative reading. If it has drifted, rarely, I tare the scales, and also try the cal. weights to double check. Re-calibration is rarely necessary.
No experience with automatic devices, other than to check some dispensing with a new RCBS Chargemaster for a friend. But was underwhelmed by the results, and the speed. OK only first try. He was satisfied with his purchase. Plenty of tips and tricks about how to improve results, mechanical mods. software fine tuning etc. I'm sure newer models may be better, but if they are all relying on a basic digital scale that only resolves to say 0.1 grain, I'm not so sure how much better they are than my manual methods, with better scales, that work sufficiently quickly for me, loading 50 or 100 at a time. Yes, powder dispensing takes me an hour or so of concentrated effort, in my batch process routine, getting every one as near as perfect as I can with very humble tools., but I'm OK with that. Others aren't, so options are available.
I'd love a magnetic force restoration balance, even one of analytical grade, but I don't think I actually need one.
The trouble is with the sort that only resolve to say 1/10 grain. Straight away you are stuck with something that can only display within a 0.2 grain window. That's before base accuracy, calibration state, warmup drift etc. I don't think that's quite good enough.
My two resolve to 1 milligram, and have a two-weight calibration routine, which is supposed to linearize the reading between the low and the high mass cal. weights, that came with them. 1 milligram is about 0.015 grains. When switched to display in grains they work in increments of 0.02 grains, according to the rounding method used internally. Natively they work in milligrams, which is how I mostly use them, just because I prefer to, and maybe have that extra edge..
I see on the LCD display a readout that could be 0.02 grains high, or low, or somewhere in-between. Plus the other errors. Not to kid myself, I still reckon they are accurate, and precise enough, to measure powder to within 0.1 grains total variation, absolute. Which is good enough for me. They will also move with just one or two kernels of stick powder, which is interesting, but I'm not one to worry about individual kernels.
They have been tested with extremely precise laboratory standard test weights, and proved to be good. As have, surprisingly, the calibration weights supplied with them..
I have two, in case one goes bad. No other reason, and it's not happened yet.
I like them, know how to check the calibration which rarely drifts after a bit of use (maybe those strain gauges settle down after a while) and use them in a "temperature controlled environment" i.e. inside my house. They run off batteries, not plugged into the mains. I don't have any striplights, which certainly can cause EMI, which I can detect through my hearing aids on the telecoil setting. Quite interesting having a "super sense" to be able to hear EMI at audible frequencies.
So, I throw an undercharge into the pan (a Lyman one with a built in funnel). Using a basic Lee Perfect Powder Measure that I've had for many years. Or even just a Lee dipper if I don't want to fill up the powder thrower.. Put on the scale and manually trickle up (RCBS trickler) Only takes a few seconds. I know what my pan weighs, so every time I lift it off the scale I observe the negative reading. If it has drifted, rarely, I tare the scales, and also try the cal. weights to double check. Re-calibration is rarely necessary.
No experience with automatic devices, other than to check some dispensing with a new RCBS Chargemaster for a friend. But was underwhelmed by the results, and the speed. OK only first try. He was satisfied with his purchase. Plenty of tips and tricks about how to improve results, mechanical mods. software fine tuning etc. I'm sure newer models may be better, but if they are all relying on a basic digital scale that only resolves to say 0.1 grain, I'm not so sure how much better they are than my manual methods, with better scales, that work sufficiently quickly for me, loading 50 or 100 at a time. Yes, powder dispensing takes me an hour or so of concentrated effort, in my batch process routine, getting every one as near as perfect as I can with very humble tools., but I'm OK with that. Others aren't, so options are available.
I'd love a magnetic force restoration balance, even one of analytical grade, but I don't think I actually need one.
Yes, the strain gauge ones usually perform better if "warmed up" (turned on) for at least 30 mins before use.
You make some very valid points. Ones that (IMHO) people should read and consider carefully.
Easy enough to check, buy some CE marked calibration weights for £13.69. 17 Pcs Calibration Weights Set, 10mg-100g Grams Weights Calibration, Precision Stainless Steel Calibration Weight Kit, Scale Calibration Weight Kit for Digital Balance Scale, Jewellery Scale : Amazon.co.uk: Business, Industry & Science
My chargemaster link and one set of £20 eBay jewellery scales are pretty accurate with these, after a 30-minute warm-up. Some of my other cheapo archery scales are way off. Never really understood sending 50g calibration weights (which is what comes with the Chargemaster) with a product you want to measure down to 0.1gr but the smallest weight in the calibration set is 10mg which is 0.15gr.
What I have been doing is zeroing the pan on both scales, throwing with the Chargemaster and then checking very occasionally on the cheapo jewellery scales. The chargemaster reads to 0.1gr and I would say it's probably there or thereabouts, certainly good enough for my range ammo. What I have found is that grains of powder hit the pan and then bounce out onto the measuring platter, that makes a difference very quickly, they need brushing off every throw. I've been using the Lee Delux powder measure and according to my cheapo scales, each throw can be plus/minus 0.3gr so I'm only using that for 'agricultural' ammo for my .303. I've also tried the Lee measuring scoop but even when used very carefully, I'd say that can be as much as 1gr out each time.
I think that before I would invest in any more accurate measuring device, I'd want to get my bullet seating technique better so that I am seating to the same depth every time and probably switch over to Lapua cases for consistency. At the moment, I have some Lapua cases but also PPU and Magtech. There is up to 1 grain variation in case weights with PPU and Magtech and as I pointed out in a different thread, if that's equal to 1gr of case volume GRT calculates that out to be a 8% pressure difference in .223 ammo. The Lapua cases in 6.5 CM showed a maximum variation of 0.4gr in weight for me, with 8/10 within 0.2gr. I should really take 50 cases and measure the case volume but that sounds like a job for next winter.
My one really big piece of learning recently was to take the volume of the cases you are going to use, the .223 default volume is 31gr, my volume is 30gr, that's an 8% difference in peak pressure. I'm still a beginner, up to about 900 reloads now, lots still to learn, I was reading today that independent of charge, not trimming cases to the correct length can cause a pressure spike.
As I understand it, the charge weight is all part of a system which includes case volume and seating depth, so for me getting those consistent would come before seeking an accuracy improvement of 0.1gr of powder, after all GRT tells me that a 0.2gr powder difference is a 3% pressure change in .223 ammo while a 1gr difference in case volume is an 8% pressure change. I'm really starting to get the reasons for sticking with manufacturers published data, including COL and seating depth.
My chargemaster link and one set of £20 eBay jewellery scales are pretty accurate with these, after a 30-minute warm-up. Some of my other cheapo archery scales are way off. Never really understood sending 50g calibration weights (which is what comes with the Chargemaster) with a product you want to measure down to 0.1gr but the smallest weight in the calibration set is 10mg which is 0.15gr.
What I have been doing is zeroing the pan on both scales, throwing with the Chargemaster and then checking very occasionally on the cheapo jewellery scales. The chargemaster reads to 0.1gr and I would say it's probably there or thereabouts, certainly good enough for my range ammo. What I have found is that grains of powder hit the pan and then bounce out onto the measuring platter, that makes a difference very quickly, they need brushing off every throw. I've been using the Lee Delux powder measure and according to my cheapo scales, each throw can be plus/minus 0.3gr so I'm only using that for 'agricultural' ammo for my .303. I've also tried the Lee measuring scoop but even when used very carefully, I'd say that can be as much as 1gr out each time.
I think that before I would invest in any more accurate measuring device, I'd want to get my bullet seating technique better so that I am seating to the same depth every time and probably switch over to Lapua cases for consistency. At the moment, I have some Lapua cases but also PPU and Magtech. There is up to 1 grain variation in case weights with PPU and Magtech and as I pointed out in a different thread, if that's equal to 1gr of case volume GRT calculates that out to be a 8% pressure difference in .223 ammo. The Lapua cases in 6.5 CM showed a maximum variation of 0.4gr in weight for me, with 8/10 within 0.2gr. I should really take 50 cases and measure the case volume but that sounds like a job for next winter.
My one really big piece of learning recently was to take the volume of the cases you are going to use, the .223 default volume is 31gr, my volume is 30gr, that's an 8% difference in peak pressure. I'm still a beginner, up to about 900 reloads now, lots still to learn, I was reading today that independent of charge, not trimming cases to the correct length can cause a pressure spike.
As I understand it, the charge weight is all part of a system which includes case volume and seating depth, so for me getting those consistent would come before seeking an accuracy improvement of 0.1gr of powder, after all GRT tells me that a 0.2gr powder difference is a 3% pressure change in .223 ammo while a 1gr difference in case volume is an 8% pressure change. I'm really starting to get the reasons for sticking with manufacturers published data, including COL and seating depth.
And make sure no kernels are hung up inside, I turn my machine upside down gently, over a large funnel, surprising how much can be hiding.Another vote for chargemaster light. - although always remember to close the drain shute cover for the next time!
Actually my cheapo ones seem to be spot on even from a cold start. However they time out after 30 minutes of dis-use. Which is scarcely a problem during a reloading session. My point about the strain gauges "settling down" was that, after a little use, they seem to have become very stable. In the first few hours, yes I detected drift, and scale error. But that soon passed. "running in" if you like. Maybe I've been lucky with mine, but I think they have become reasonably consistent and trustworthy with some hours of use on them.
Simple enough, at the start of a session check and if necessary reset the tare with an empty pan. I've marked my pan/funnel with its weight, so when I lift it off each time I expect to see that weight registering as a negative reading. I just glance at the last two digits. Put on a calibration weight. If that reads correctly, which it usually does, they are good to go.
Just treat them carefully, don't overload, and don't bash them about. Keep an eye on them during use, that the tare hasn't drifted, put on a calibration weight every now and then to check the scale factor. And don't let the batteries run too low.
After filling a batch of cases, go back and re-weigh a few at random, just to be sure. Then move on to seating the bullets.
Of course use them on a level surface, free from vibration. Any slight tilt will reduce the weight measured. This can to an extent be calibrated out, but basically keep them in the same place on your (solid) bench during use. Whether they are just scales, or an automated device.
I'm not sure about your numbers. Brass has a density about 8.5 times that of water. So 1gr variation in case weight might represent only about 0.12gr variation in water capacity. Not a whole grain.
If indeed such weight variances directly translate into internal volume differences, some might just be things like the machining of the extractor grooves in the heads, or the thickness of the rims. Then what difference might there be between a new piece of brass, and one that's been fire formed, neck sized or FL resized ?
Powders typically have a VMD between 0.07 and 0,1 cc/gr. Lets say 10 grains/cc. That's 0.65 grams/cc. at most. 0.65 times the density of water. https://leeprecision.com/files/instruct/VMD.pdf
So that 0.12 gr (i.e. 0.0778 grams, or cc) difference in case water capacity represents only about 0.12x0.65 = 0.08 grains of powder space variation. Or less.
Or, look at it another way, for a 223 case, 5.56mm diameter bullet, it would take a seating depth variation of 3.2mm (126/1000") to vary the internal case volume by 0.0778cc
Therefore I suspect that brass weight variations of 1 grain, or seating depth variations of 125/1000" would only have similar effects as powder weight variances of less than 0.1 grains. QED I think that getting the powder weight precise is more important than worrying too much about brass weight or seating depth variances.
If say you are trying to develop a load using charge weight variations of 0.3 or 0.5 grains at a time, yet your measuring device can only be trusted to be within 0.2 grains, I'd say it's probably not good enough. I reckon to measure my powder to within rather better than 0.1 grains, if I'm trying to make the best ammo I can. Probably not necessary, but I can do it. Other times I just throw charges with my Lee Perfect Powder Measure, but weigh every one. Those that are outside my arbitrary tolerance band, maybe 0.5 grains, are put back in the hopper and I throw another one.
I'm sure you are absolutely correct when talking about a solid lump of brass, however, I do not know if you are correct when talking about brass shaped into a cylinder when that weight difference is effectively shaped across three dimensions to contain a volume of water. Now we are asking how much surface area does that 1gr equate to which is a thickness of brass question, rather than how much volume of brass.
The relationship between volume and pressure is not linear, a 3% difference in volume is an 8% difference in pressure, I suspect that bullet seating has a greater effect than charge variation at the levels we are discussing.
I have no way to be sure without doing the work, when I find time I will measure the water capacity of 50 (PPU/Magtech) cases when I have fired them and before decapping and report back the results.
Last edited:
Ummm...everyone understands that the greatest variation in a case is the case rim itself, right? It's machined, and not necessarily to exacting tolerances...making weighing brass a fool's errand. I, for the life of me, don't understand why most people do not understand this, or know this. This has been tested, and documented by Bryan Litz. It is why he does not recommend weighing brass as a means of comparing uniformity of cases, or their represented volumes. It's very hard to measure the uniformity of the case rim cut, but even small variances cause a huge swing in case weight.
I'm pretty sure that I am correct. And that you are over grossly-thinking this. A case is made of brass, specific gravity approximately 8.5., depending on precise alloy composition. Doesn't matter how its made., for the same external dimensions (which are finely controlled for gun brass), the hollow bit inside is where the powder fits. It is filled with air, or powder, or a combination. There are only so many ccs of brass, and so many ccs of air space inside., which are fairly easily calculated It can be measured straightforwardly by the water filling method. 1cc of water weighs 1 gram. Minus a simple calculation to correct for the length of bullet shank inserted.
The case has an external volume of x (taking into account things like the machining of the rim). The mass of brass in it has a volume of y (according to the actual density of the brass in question, which can be quite variable). So has an internal volume of z. x-y = z. Not that I think the overall result is particularly sensitive to small variations of internal volume. Despite what a simulator might suggest.
Just as no simulator can predict the peculiarities of how ammo really works, when tested over a chrono or on paper, using e.g. optimal charge weight approaches, when accuracy nodes can be found where significant charge weight variations make little difference to the velocity, or extreme spread, or the vertical drops.
By the way, Gordon's Reloading Tool is not being updated since Gordon died, in January, and AFAIK there is no immediate plan for succession. So, interesting though it is, it's not something that I care to study too deeply at the moment. I do hope it is taken on by other developers in future.
To worry you, I should point out that SAAMI, CIP and so on don't specify the internal dimensions of the brass, nor the alloy composition. That's down to the manufacturer to decide, knowing the maximum pressure allowed, whether they intend it to be reloaded, even anticipating that some will push their reloads very hot, well above specified pressure, overall precision, cost constraints. It is not all equal.
As you reload it, and the brass flows forward until its time to trim it off at the neck to keep it fitting in the chamber, not pinching the bullet between the end of the neck and the freebore portion (which is the risk if you let it lengthen excessively, hence possible pressure problems because basically the bullet is jammed into it) you lose a bit. You can easily work out how much is lost in say trimming back from max. length (i.e. do not exceed) to "trim to" length, typically you'd be shaving off 0.015"
Here's an example:
Try calculating the weight of an annulus of brass, density 8.5 g/cc, length 0.76 mm, internal diameter 5.702 mm, external diameter 6.43mm. That would represent a full trim, all the way back from max. to min. not the usual halfway point. The sort of process that would only be needed after many reloadings. Or chipped away at by those who think it's necessary to trim every time. I'll leave you to work that out yourself.
Succinctly put. Just because you can easily measure something doesn't mean it matters much at all. Other measurements do, but brass weight variations are not one of these. IMO.
You need to log into the Discord server for GRT, they have had a huge response to their call for programmers and what was already released still works, after all, how often does QL get updated? There is a worldwide community of people dedicated to keeping Gordon's work alive but if you see no use or value in the tool then I'm the last person to suggest that you use it, it's there to be used or ignored as you wish. I know they have paused the crowdsourcing of data but I really hope they open it up again, as I bought a chrono especially so I could contribute and I have a pile of .303 and .223 data to upload. I have been following along and I think it will take them a year to pick up Gordon's work and move forward but in the meanwhile, GRT is still available and I am happy to continue to use the version from last November.
As for the rest of it, forgive me if I would rather measure for myself than trust the opinions of the internet, but thank you very much for your valuable and informative input. I have 200 new Lapua cases and I will track their case volume across firing, resizing and trimming and see what that shows and also work on achieving the most consistent seating depth that I can. As I have said previously, I'm pretty happy with the performance of my Chargemaster Link after measuring it with the calibration weights.
As for the rest of it, forgive me if I would rather measure for myself than trust the opinions of the internet, but thank you very much for your valuable and informative input. I have 200 new Lapua cases and I will track their case volume across firing, resizing and trimming and see what that shows and also work on achieving the most consistent seating depth that I can. As I have said previously, I'm pretty happy with the performance of my Chargemaster Link after measuring it with the calibration weights.
I have not dug deep into GRT, nor considered buying QuickLoad, because for what I do I find @borbal 's P-Max simulator sufficient for me to get a handle on pressure, muzzle velocity etc. choose a powder that looks promising (pressure, case fill, % burn, likely muzzle velocity) and also sanity check of published reload data from other sources. For which it usually matches quite closely to published data that comes from actual measurements in test barrels.
P-Max internal ballistics
I am pleased to hear that GRT may continue to be developed. But you could also give P-Max a try as well. I think it does most of what I need quite well, and is quick and simple to use.
That sounds like an interesting project. And good to hear that your Chargemaster is doing the job, as double checked with your other scales. And even your set of weights. Just because it can measure your test weights to within the limits of its resolution, +/- 0.1 gr, doesn't necessarily mean that it also throws the charges any better than that. Best to measure them with say 1 milligram/0.02 grain jewellery scales as well until you have confidence that it is doing better than that. It may even be possible that internally it works from a higher resolution than the display actually shows you. Nevertheless, in the limit, the Chargemaster scale alone cannot show an undercharge, or an overcharge, until it is outside that 0.2gr window. Plus other errors.
The idea of calibrating a strain gauge digital scale with weights of larger than the usual powder (plus pan) amount, is that the strain gauge and electronic A-D convertor are hopefully linear over the whole range, but aren't always. The two point calibration of the better ones is supposed to do a curve-fit between say zero, half and full scale, to optimise that. Do it over say the 100g range of a scale, then when using it at the lower weight of a normal charge, plus pan, and you benefit from that. A magnetic force restoration balance doesn't need a two point, plus zero, calibration. Just a full scale and zero, because they are inherently linear. Strain gauge types may not be.
Regard those inexpensive smaller weights as "check weights", not calibration standards. To give confidence that your scales are in the ballpark For linearity, motonicity etc. Or for use in two-pan scales. That's enough about the scales.
Meanwhile here a few "what ifs" that I've just run through P-Max using a pet load for .223 that I used to use in quantity. It's not a "hot" load. P-Max does not directly affect the most important thing, which is the velocity with which the bullets come out of the muzzle. Providing the P-Max is within sensible limits.
223 Rem. 55gr jacketed lead bullet. 24" barrel. 27gr of Vectan SP7.
Assumptions:
1 gr variation in case weight, which I have already calculated to probably result in only 0.12 gr variation in water capacity, if that. Even less than 0.1 graind of actual powder capacity variation. I'm fairly sure of that .
Or a variation in seating depth of 125/1000", (which is a lot) also resulting in 0.12gr variation in water capacity. Same thing.
Or identical case capacity, but a variation in powder weight of 0.2 gr.
Using the suggested case capacity of 28.4 gr up to the neck/shoulder junction. But measure your own brass and correct for the amount of bullet shank inside the case, at your seating depth. Or even do it the precise way, filling up the case through the flash hole with a syringe, with a bullet seated at your chosen depth.
Here is a screengrab of how the input data looks, at baseline:
So, baseline, my pet load has a simulated P-Max of 42,640 PSI. Well inside the 223 SAAMI spec of 55,000. Not approaching "hot".
Load density is good, 96%. So is powder burn inside the barrel, also 96%
Reducing the case capacity due to brass weight variations, (or the seating depth) by 0.12 gr of water capacity results in a P-Max of 43114 psi. A 1.11 % increase. Not the 8% figure that you have come up with by I think mis-assuming that brass has the same density as water, then plugging that into your simulation. This, I think, is your basic error. As is your idea that small seating depth variations are likely to have much significance. They may affect accuracy or consistency, for other reasons of course. As may primer choice, neck tension, crimping or not, jump to the lands etc.
Muzzle velocity rises from 3215 to 3224 fps. A 9 fps change.
So, let's see what a 0.2 gr powder weight variation might do instead. This could be the spread of a powder thrower, or scales, that only resolve to +/- 0.1 grains
This time P-Max is at 43,895 psi. A 3% increase. I'm not bothered, it nowhere near worrying levels.
Muzzle velocity has risen to 3248 fps. a 33 fps increase. Which starts to become significant when shooting at say 300 metres plus. Consult an external ballistic calculator to estimate how that might move the vertical, at your distances. It's also the sort of level that people who chrono every shot start to worry about, when it shows up as extreme spread, over a significant number of shots.
Which is why I suggest that minor brass weight, or seating depth variations, may have rather less relevance to results than weighing your powder as precisely as you can. Whether it be by hand, or with an automatic device. For many, if not most, just getting it within 0.2 gr and hopefully rather better, will still be good enough.
Consistent seating depth is not difficult, provided you are using a comparator to measure CBTO. Even the humblest Lee seater die can do a good job of that. Measuring the simple way, COAL is not good enough IMO
The energy in the powder is what acts on the bullet. Directly related to the mass of powder.
The volume of the powder space inside the assembled cartridge has a second order effect, but has no direct consequence on the energy contained in a fixed mass of powder. Providing it is pretty well all fully consumed whilst still inside the barrel. Some even use compressed loads. How do you regard those, if fretting over tiny changes in case powder capacity ?
P-Max only applies in the first 1.5 inches or so of the bullet travel, after that the bullet continues to accelerate as the pressure drops markedly, down the full length of barrel and the powder continues to burn/deflagrate. Ideally 100% of it inside the barrel. In my simulations that was 96% burn irrespective of the small powder space variations. Yet 97% when using the increased charge of powder. Which I attribute to the higher P-Max speeding up the burn rate of the powder slightly.
There is nothing like a linear relationship between P-Max, and muzzle velocity. Higher P-Max can increase the powder burn rate, but not the total amount of energy contained in it. Just as the powder space inside the cartridge case has less and less relevance as the bullet travels further down the barrel and the volume inside which the powder is burning increases to far more than the original cartridge case volume.
The larger the case, and the heavier the powder charge, the less significance these things have, in absolute terms. Shooting 223 or similar sized things, precisely, at say 300 -600 m with maybe 27 gr of powder requires more attention to detail in powder measurement than say 308, or other such cases, 6.5CM etc. that might take about 44 gr of powder. Just as something small, like a hornet, that only takes half that amount of powder will be doubly sensitive to small powder weight variations. But those sorts of things aren't generally shot at longer ranges, so it probably doesn't matter as much.
These are just my thoughts on the subject. Please don't let me distract you from yours.
I would just like to comment that Sharpie is using the P-Max online internal ballistics simulator in exactly the way it should be used.
It works very well in zeroing in on the best powder for your particular cartridge/bullet/barrel combination and there are over 120 powders to choose from. The powder that gives the most 'balanced' load is one which give a good working pressure when it fills the case. (That is, the space behind the loaded bullet is filled up with powder). And, it should be all-burnt when the bullet exits the barrel.
More particularly, the powder charge should be *just* all-burnt to give you the best velocity. Powders that are all-burnt well before the bullet exits the barrel are generally too fast and you will need high maximum pressures to get decent muzzle velocities. If the powder charge is not all-burnt on bullet launch then, of course, you are just wasting powder. Do not be too pedantic about this though.... If P-Max says 97% or 98% of the powder is burnt then you are in the right ballpark. This is useful for rifles with particularly short barrels where you might want to use a slightly faster powder than those with relatively long barrels.
Once you have the right powder, P-Max will give you a reasonable idea on the maximum pressure and muzzle velocity you might expect, and give you a feel for how these will change if you change the load. These are indications and trends, not numbers to be taken as though they were measurements from a test barrel.
That said, I find that predicted muzzle velocities are usually within about 3% (say, 100ft/sec.) The estimated maximum pressure has a coloured background which can be green (as in the screenshot above), amber, or red. I usually find that the estimated pressures for the starting loads in reloading handbooks are 'green', and the maximum load pressure is usually 'amber'. This is generally as it should be and it gives me some satisfaction to see that P-Max is doing a reasonable job of modelling the internal ballistics. If you find that P-Max indicates a 'red' pressure for a given load, then you definitely don't want to explore that!
I should add that just because isentropic ratios, burning rate coefficients, powder potentials and a host of other variables are not listed on the screen does not mean they are not there 'under the hood'. The P-Max internal ballistic numerical model is every bit as sophisticated as that used in Quickload or GRT.
It works very well in zeroing in on the best powder for your particular cartridge/bullet/barrel combination and there are over 120 powders to choose from. The powder that gives the most 'balanced' load is one which give a good working pressure when it fills the case. (That is, the space behind the loaded bullet is filled up with powder). And, it should be all-burnt when the bullet exits the barrel.
More particularly, the powder charge should be *just* all-burnt to give you the best velocity. Powders that are all-burnt well before the bullet exits the barrel are generally too fast and you will need high maximum pressures to get decent muzzle velocities. If the powder charge is not all-burnt on bullet launch then, of course, you are just wasting powder. Do not be too pedantic about this though.... If P-Max says 97% or 98% of the powder is burnt then you are in the right ballpark. This is useful for rifles with particularly short barrels where you might want to use a slightly faster powder than those with relatively long barrels.
Once you have the right powder, P-Max will give you a reasonable idea on the maximum pressure and muzzle velocity you might expect, and give you a feel for how these will change if you change the load. These are indications and trends, not numbers to be taken as though they were measurements from a test barrel.
That said, I find that predicted muzzle velocities are usually within about 3% (say, 100ft/sec.) The estimated maximum pressure has a coloured background which can be green (as in the screenshot above), amber, or red. I usually find that the estimated pressures for the starting loads in reloading handbooks are 'green', and the maximum load pressure is usually 'amber'. This is generally as it should be and it gives me some satisfaction to see that P-Max is doing a reasonable job of modelling the internal ballistics. If you find that P-Max indicates a 'red' pressure for a given load, then you definitely don't want to explore that!
I should add that just because isentropic ratios, burning rate coefficients, powder potentials and a host of other variables are not listed on the screen does not mean they are not there 'under the hood'. The P-Max internal ballistic numerical model is every bit as sophisticated as that used in Quickload or GRT.
Actually, given the accuracy of these simulator models, I would say that was complete agreement!
3% difference in PMax, 1.4" travel to PMax in one, 3.7" in the other, makes me wonder if they are measuring from different points.
As you say, the rest is within 1% or so
The Viht published max loads seem to come up between PMax -20% and PMax -10% in GRT, less conservative with .303 (PMax -10%), very conservative with 6.5CM (PMax -20%)
As you say, the rest is within 1% or so
The Viht published max loads seem to come up between PMax -20% and PMax -10% in GRT, less conservative with .303 (PMax -10%), very conservative with 6.5CM (PMax -20%)
Similar threads
