GRT - What Am I Doing Wrong?

[Alantoo]

Though I suspect that simply sorting the cases by dry weight would be good enough

What is "good enough" and what is critical?

I read somewhere that there is more variation between case weights than case volumes...the reason given was that the machined extraction groove had relatively greater tolerance. So if you want to sort cases by volume then it is best to compare volumes rather than weights.

It was the minutiae / significance of ignoring the primer volume in the GRT/P-MAX simulation context that I was intrigued by...if the 1gr variation between case brand/batch volume is significant, then why isn't the 0.5gr volume of the primer void? I guess because it is fairly constant.

Alan

Case Capacity

After finishing up working on an M1A I decided to investigate an issue my shooting friends and I had recently discussed, namely the issue of case capacity for various manufacturers. I chose .308 Winchester for the test since we are all using that brass and I have 6 or 7 different brands. The...

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QuickLOAD Review & User's Guide

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[Sharpie]

Actually, I did order it from Julian, but cancelled the order when I found out how archaic it was and then found GRT, which is modern software that works well. Sorry, I didn't respond immediately to your idiotic non-solution but I was out having a great day in beautiful weather at Bisley. I think it probably best we ignore each other from now on, I've certainly pressed the ignore button on you, you witter on fatuously pointing to other people's work without adding anything useful yourself or it appears doing any shooting. As far as I know QL woks well but if it is not available in a format I can use, then I'm not jumping through hoops to use it. I will also not be taking up your kind offer for me to buy QL for you to then send me a pirated copy, while you keep the original.

Hmm, you seem to have become somewhat twisted and bitter since you first introduced yourself here, on 20 March. And have so far made another 65 posts.

Lets deconstruct what you have to say:

QL is "archaic", GRT is "modern". In your head maybe.

As noted in the GRT manual:

"ALTERNATIVE
The commercially available software "QuickLoad" was our standard. We support and respect the
outstanding work of Mr. Brömel with his software.
We still have many ideas for the GRT. Our intention was and is not only to create an alternative, but also a platform
that can grow by a community"

"Idiotic non-solution". Actually a perfectly genuine offer, though I could think you to be the idiot for not being able to do this for yourself.

"As far as I know QL works well". But you don't do you, because you haven't tried it. So far your knowledge of simulation appears to be purely based on having tried out GRT. And BTW, made a fundamental error earlier on when you assumed that brass and water had the same density, then questioned my polite correction, saying that you didn't believe me, only trusted things that you had tried out yourself.

"I'm not jumping through hoops ...". Clearly not. Or just lazy and impatient.

"send me a pirated copy, while you keep the original". Now that is a truly offensive, twisted remark. A decent person would apologise for saying such a thing.

"I've certainly pressed the ignore button on you". So you won't be reading this then. Probably for the best.

 

[Sharpie]

What is "good enough" and what is critical?

I read somewhere that there is more variation between case weights than case volumes...the reason given was that the machined extraction groove had relatively greater tolerance. So if you want to sort cases by volume then it is best to compare volumes rather than weights.

It was the minutiae / significance of ignoring the primer volume in the GRT/P-MAX simulation context that I was intrigued by...if the 1gr variation between case brand/batch volume is significant, then why isn't the 0.5gr volume of the primer void? I guess because it is fairly constant.

Alan

Case Capacity

After finishing up working on an M1A I decided to investigate an issue my shooting friends and I had recently discussed, namely the issue of case capacity for various manufacturers. I chose .308 Winchester for the test since we are all using that brass and I have 6 or 7 different brands. The...

www.m14forum.com

QuickLOAD Review & User's Guide

6mmBR.com is the best guide for 6mm BR Benchrest precision shooting, complete with 6BR FAQ, Reloading Data, Shooter Message Boards, Reader Polls, and Photo Gallery. Match event calendar and rifle competition accuracy training tips. Equipment reviews (.243 bullets, 30BR cartridge, 6mm Norma...

www.6mmbr.com

Indeed, this is a possible concern about simply sorting by dry weight, as we discussed on another thread. And why I said "you'll never know until you have tried". I haven't, myself.

But as for a 1gr variation in the weight of brass, you have to understand that, since brass has a specific gravity of about 8.5, that would represent a mere 0.125 gr difference in water capacity, even if directly translated into the internal volume of the case, rather than e.g. variations in the machining of the external features. Hence my mild scepticism.

And agreement that the space inside the primer itself is probably of more relevance, albeit pretty constant, but statistically insignificant.

I can actually see these primer pocket plugs as being useful in some ultra precision workflows, but hardly a "must have", at least for me.

 

[Sharpie]

Further: I was referring to sorting brass, by weight, from a single manufacturer, preferably all from the same manufacturing lot (as e.g. Lapua record). Which I see as probably a useful thing to do, as a first step, with new stuff, to find any outliers, and get a feel for how tightly controlled the case forming has been..

After that, the water-fill test.

After brass has been reloaded a few times I suspect the weight check becomes less useful, as pieces are trimmed off etc.

It's not a useful method when comparing between different manufacturers, as the density of brass can vary quite widely, according to the alloy composition (primarily copper and zinc). So you could have cases from different manufacturers with widely varying weights, yet very similar powder space, or vice versa.

Indeed it might be interesting to compare the density of brasses used by different manufacturers, perhaps this might give some insight into why say Hornady brass has a reputation for being "soft", Lapua has a good reputation, PPU has mixed reports and so on. Even small changes in the copper/zinc ratio might have economic significance to the manufacturer, zinc being very much less expensive than copper, for example.

I use the figure of 8.5 as the specific gravity in my estimations, because it is easy to remember, not because I think it is correct. That's the normal figure for straight 60:40 brass (actually its 8.52).

Could be between say 8.4 and 8.73

Brass - Wikipedia

 

[Muir]

To properly consider volume by weight, all brass must be prepped identically. I FL resize spotlessly clean brass (even new) and then trim to uniform length. From what i've read so far, my method would not be applicable To GRT. I use this to adjust loads between makes of brass, such as switching from commercial 308 brass to military 7.62.

I wanted to adjust my girlfriend's 308 target loads for use mil-spec 308. I used 40 pcs of brass from each LOT compared. I enlisted her help (under the guise of useful instruction) because it it a long and tedious process. We hit her target velocity within 20 fps average after adjusting the load for the heavier brass. Accuracy is suprisingly good if your test sample is large enough. ~Muir

 

[Alantoo]

But as for a 1gr variation in the weight of brass

You seem to have skim read and re-worded my posts again...I didn't mention a 1gr variation in the weight of brass....it was a 1gr variation in volume as in water weight gleaned from various sources....some of which I provided links to.

if the 1gr variation between case brand/batch volume is significant

The volume difference between brands and batches of cases and the chambers they have expanded into, is also going to be fairly small, around 1gr but apparently worth our measuring with water as it is specific to our rifle and our brass.

But I don't dispute your figures or conclusion. Just setting the record straight.

Alan

 

[Sharpie]

To properly consider volume by weight, all brass must be prepped identically. I FL resize spotlessly clean brass (even new) and then trim to uniform length. From what i've read so far, my method would not be applicable To GRT. I use this to adjust loads between makes of brass, such as switching from commercial 308 brass to military 7.62.

I wanted to adjust my girlfriend's 308 target loads for use mil-spec 308. I used 40 pcs of brass from each LOT compared. I enlisted her help (under the guise of useful instruction) because it it a long and tedious process. We hit her target velocity within 20 fps average after adjusting the load for the heavier brass. Accuracy is suprisingly good if your test sample is large enough. ~Muir

I agree with all of that. Except that you have assumed that your commercial 308 and the mil-spec cases are made from very similar brass density. TBH I think that's not too unreasonable. Thus-therefore there is a direct relationship between case weight and powder space. Clearly this has worked for you.

However doing a water fill comparison would tell you exactly what you have got, might be interesting to go back and compare.

Yes, to use a simulator you do need to know the actual case capacity, grains of water, either measured with a seated bullet via the flash hole (the precise way), or done by filling up to the case mouth, then correcting for the amount of bullet shank inside when seated at your COAL.

This is where QL and GRT can automate the calculation for the correction, using their bullet libraries. Which may or may not be correct. With borbal's P-Max, you have to manually calculate this correction, having measured your own bullet length. Or cut to the chase and use the flash hole fill method in the first place. Which is not difficult, and probably what you should be doing anyway.

Once you know that, then a simulator could get you very close to knowing how much to reduce the powder charge for the mil-spec brass to achieve the identical muzzle velocity, and also show you how the Pmax has changed in doing so. In case it is getting hairy.

Yes, the brass must be identically prepped, whether that be new, straight out of the box, or once-fired and left as such, or FL sized.

I think the critical thing, whether using the water-fill from the neck method, or weighing, is that all the pieces are trimmed to the same length.

 

[Muir]

Agreed on above. Especially the prep part. It is essential. I also believe that a large sample is equaly so. IT would be interesting to repeat the process using Gordons but I probably won't. Eighty cases? I haven't got that much time left on the sunny side of the turf!

This method has worked for me for many years but I only use it at need. That volume determination is important is with out question. I sampled 20 new NAMO and 20 new Lapua cases. (308) The NAMO averaged 10 grains heavier in like prepped cases. Food for thought to a thoughtful reloader. ~Muir

 

[Sharpie]

You seem to have skim read and re-worded my posts again...I didn't mention a 1gr variation in the weight of brass....it was a 1gr variation in volume as in water weight gleaned from various sources....some of which I provided links to.



But I don't dispute your figures or conclusion. Just setting the record straight.

Alan

I put my hands up. I am a very naughty boy, and also did not look at your links

But of course, if you are mixing brass, a simulator can help show you how such volume variations might affect results.

As to whether measuring the actual volume, or simply sorting by weight is better, that's moot. But consider, if, and it's a big if, the brass is all of the same density, and the external features are machined closely, then the sorting by weight method could be 8.5 times more precise than the water-fill technique.

I.e. for an actual 1gr variation in measured water capacity, you might expect an 8.5 gr variation in brass weight.

Of course this assumes perfectly clean inside, no powder residue. BTW, what do you reckon the volume, or weight, of that might be inside a very dirty case ? (Only joking).

 

[Sharpie]

Agreed on above. Especially the prep part. It is essential. I also believe that a large sample is equaly so. IT would be interesting to repeat the process using Gordons but I probably won't. Eighty cases? I haven't got that much time left on the sunny side of the turf!

This method has worked for me for many years but I only use it at need. That volume determination is important is with out question. I sampled 20 new NAMO and 20 new Lapua cases. (308) The NAMO averaged 10 grains heavier in like prepped cases. Food for thought to a thoughtful reloader. ~Muir

Case prep, i.e. trimming. Consider a 308 case subject to a trim from max. all the way down to min. 0.18 mm (0.007")

That's an annulus of brass. Inner radius 7.82 mm. Outer radius 8.58 mm say.

Meaning you've trimmed off 7 mm^3 of brass. About 60 mg, or 0.93 grains. You can certainly measure that, but in terms of possible water capacity variance its still only 7 mg. Or 0.1 grains. Which is pretty small as far as effect on the internal ballistics. Still prudent to make sure your cases are somewhere between max. and "trim to" length, as you should be doing anyway. That cuts my calculated figure in half, to 0.05 gr. So, actually, variations in case length within allowable limits are almost insignificant when simply weighing.

If you are doing water fill through the neck, that 0.18 mm of length variation would represent 8.65 mg, or 0.13 gr. Again, not worth worrying about

As for a 10 grain difference between NAMO and Lapua, if they are of identical brass composition that could mean they differ in volume by 1.18 gr of water. This is likely to become significant in a simulation, particularly if you are using loads towards the top end of Pmax.

Really there is no substitute for measuring a sample of each with water.

TBH I wouldn't bother to do much more than sort by weight, then choose three, or even just one, of average weight, to do the water fill measurement. Once you have that your ready for some simulation, starting off by entering a known load that you have chronoed, I'd suggest, and see how close it gets.

 

[Sharpie]

Oops, when I said radius when talking about how much brass gets trimmed off, I stated diameters Divide by two. Which I did in my estimates, which I think are correct. Just so as you know and before you jump on me.

Pi R^2 and all that.

Annulus: A=π(R2﹣r2)

Or, you could go back to basics, (really basic, but certainly not as bad as Lee Loader aficionados do) and observe what "letshuntdinner" proposes. Though I suspect that he does it rather better usually.

 

[Bavarianbrit]

Rather than starting a new thread I thought I would add this to the knowledge pool.
I have an 8x56R Sauer drilling that I am beginning to reload for, the cases are hard to find but I have 25x but they are berdan primed. So off go I to Nurnberg today to the gun store for some 5.5mm diameter berdan primers. "Do you need the 2.5mm deep ones or the 2.7mm deep ones"? Says the sales person. Er, "I will get back to you" say I.
I never have read anywhere that berdans can be available in different depths before. Now where did I leave my depth micrometer?
Every day is a school day.

 

[Dr. Strangelove]

Understood - I was using the RS temperature coefficient data here - Reload Swiss temperature coefficient. Unless I'm wrong, and I could be, that '0.25ms pro K' figure equates to 0.82fps per degree Celcius. Or about a 24.6fps change for a 30deg C swing in temp. The data they posted is for 8x68 S but I figured it might extrapolate across irrespective of cartridge. With the '0.55ms pro K' data, that equates (I think) to around a 54fps swing over 30deg C. Not massive!

@Laurie - any thoughts on my above post in terms of RS60 temp stability?