The thing is that you might spend time and effort achieving your goal of 1 MOA but then when you get the next LOT of factory ammo, you might get different results -especially if it's bargain ammo to begin with.~Muir
Altering seating depth on factory ammo to tighten groups
- Thread starter nun_hunter
- Start date
nun_hunter
Well-Known Member
Very true and not something I had considered actually. This is why it pays to ask questions and save wasting some time (at least my time, I've wasted plenty of other members time with having them write replies on here!) but all adds to the fact you can learn new stuff every day.
The original question was not an unreasonable one, from someone who has a logical/inquiring mind.
No-one else seems to have thought about trying it.
When you get the bullet out, please post the depth of the crimp so that I can compare it with my results using the Lee Factory Crimp Die on several different bullets.
No-one else seems to have thought about trying it.
When you get the bullet out, please post the depth of the crimp so that I can compare it with my results using the Lee Factory Crimp Die on several different bullets.
Well, contrary to popular opinion it seems, I’m going to agree with you! and for no other reason than I agree with your logic and that Im sure you’ll find the results interesting.
Also I’m going to disagree with what appears to be the popular opinion, that you don’t need to worry about producing/ procuring particularly accurate ammunition if you’re going to be shooting it at something the size of a deer and at ranges less than three hundred yards. I feel that before I’m prepared to discharge my rifle at a living beast, I have a duty to know exactly where the bullet is going to go, and that it’s capable of doing the job.
By the sound of things, I develop loads exactly the same way as you. That is choose the powder charge your going to test, load up 15 or so rounds in two tenths of a grain increments up to and beyond your chosen weight, then fire them across a chronograph, your looking for two or three consecutive loads that are giving very close velocity levels, doesn’t matter what the group size is at this stage. your looking for the charge weight which gives very consistent pressure levels with the given case volume neck tension etc.
Once you’ve got your bullets all going down the barrel at the same velocity, you look to reduce group size by adjusting the seating depth, so altering the point at which the bullet leaves the muzzle in the vibration/harmonic cycle.
All is well and good if all of these variables result in achieving an accurate load at the velocity levels required for the given task. If it doesn’t, you might have to start all over again with a different powder, case, primer or bullet.
In your case, as most factory rounds are (as a result of having to produce a round which will fit all rifles of that caliber) seated well short of the lands, you’ll be adjusting the seating depth outwards, ( I wouldn’t try to seat deeper as you’ll be increasing pressure and even minute reductions in case volume can cause peculiar increases in pressure in some powders and you probably don’t know which powder you’re dealing with) In which case you shouldn’t have any problems as long as you don’t go to close to the lands, I’d go no closer than 0.030” off.
As has been stated, you’ll not achieve anything more than you could achieve by reloading, but if it floats your boat, why not !
Also I’m going to disagree with what appears to be the popular opinion, that you don’t need to worry about producing/ procuring particularly accurate ammunition if you’re going to be shooting it at something the size of a deer and at ranges less than three hundred yards. I feel that before I’m prepared to discharge my rifle at a living beast, I have a duty to know exactly where the bullet is going to go, and that it’s capable of doing the job.
By the sound of things, I develop loads exactly the same way as you. That is choose the powder charge your going to test, load up 15 or so rounds in two tenths of a grain increments up to and beyond your chosen weight, then fire them across a chronograph, your looking for two or three consecutive loads that are giving very close velocity levels, doesn’t matter what the group size is at this stage. your looking for the charge weight which gives very consistent pressure levels with the given case volume neck tension etc.
Once you’ve got your bullets all going down the barrel at the same velocity, you look to reduce group size by adjusting the seating depth, so altering the point at which the bullet leaves the muzzle in the vibration/harmonic cycle.
All is well and good if all of these variables result in achieving an accurate load at the velocity levels required for the given task. If it doesn’t, you might have to start all over again with a different powder, case, primer or bullet.
In your case, as most factory rounds are (as a result of having to produce a round which will fit all rifles of that caliber) seated well short of the lands, you’ll be adjusting the seating depth outwards, ( I wouldn’t try to seat deeper as you’ll be increasing pressure and even minute reductions in case volume can cause peculiar increases in pressure in some powders and you probably don’t know which powder you’re dealing with) In which case you shouldn’t have any problems as long as you don’t go to close to the lands, I’d go no closer than 0.030” off.
As has been stated, you’ll not achieve anything more than you could achieve by reloading, but if it floats your boat, why not !
Morning Muir,
Ive underlined his opening statement, I’d say this looks to me as though he’s had success with the OCW method. May have misread something else later.
I must say it works well for me. I don’t even use a target now when I’m developing the powder weight element.
The advantage being I don’t need to treck to the range I use, until I’m ready to adjust the seating depth.
Morning again Muir,
Ive read post#10 again and then again, in fairness having read it I’m not quite sure what he’s trying to say. However if he’s got the sort of enquiring mind which he appears to, there’s nothing wrong in what he’s suggesting, as long as he’s not putting himself or others at risk. After all “there’s no eye as blind as a closed mind”.
Ive read post#10 again and then again, in fairness having read it I’m not quite sure what he’s trying to say. However if he’s got the sort of enquiring mind which he appears to, there’s nothing wrong in what he’s suggesting, as long as he’s not putting himself or others at risk. After all “there’s no eye as blind as a closed mind”.
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There are some faults in the reasoning in this post.
1) A factory sporting cartridge is unlikely to be loaded to the optimum pressure level for accuracy- if it is in your rifle that's plain luck, whereas you are comparing this situation to that of one of your handload recipes whose charge has been determined using OCW. Sporting ammunition manufacturers usually load their cartridges up to something close to the SAAMI MAP level to produce a high nominal MV - that's what sells cartridges to the average user, so if the SAAMI MAP is say 60,000 psi, a typical factory sporting cartridge is loaded to 57,000-58,000 psi in an industry standard pressure barrel. That may or may not be anywhere near the OCW mid point in your rifle whose barrel and chamber are unlikely to conform exactly (or in some cases even closely) to the industry standard if mass produced.
2) The reason that the GB NRA's contract 308 Win ammunition works so well in a large number of rifles is twofold. First, it is loaded with the original 155gn 0.3083" dia. Sierra MatchKing, one of the most tolerant tangent ogive bullet designs known to man and rifle builder. Secondly, the other side of the partnership - the barrel - sees near 100% conformity to a small range of variables in Fullbore / Palma / GB & Commonwealth 'Target Rifle'. That is standard 'Palma' contour blanks that have been bored and rifled slightly undersize compared to the SAAMI 0.300/0.3080 bore / groove diameters making them marginally 'tight', and chambered with one of a very small range of chamber designs, in the UK the 'Bisley 150' chamber the norm for many years (and for all I know still the primary one in use today). Barrel lengths range from 30-32" but a very high percentage will be at 30-inches. The NRA contract's starting point is that the ammunition must work well precision-wise (in terms of mean radius group sizes) and deliver 2,925-2,950 fps with acceptable ES Values with this single proven bullet design in a range of existing privately owned rifles with various barrel round counts / states of wear. When the original RUAG ammunition was selected, the manufacturer had to provide samples which were blind-tested by a group of top GB TR shooters at Bisley against alternatives in a group of rifles using the most popular barrel makes and with various states of wear. (The blind testing saw an NRA 'assistant' load cartridges into each shooter's rifle so that the shooter didn't know which make / model was being used in any given shot and couldn't therefore be psychologically influenced.)
The same thing could be done in Scandinavian prone match shooting where everybody uses the Sauer STR 200 rifle with barrels from the same source in either 308 Win or 6.5X55mm. (But in three optional barrel lengths which is an interesting and complication factor to throw into the mix!)
3) Linked to 2) it has been said often enough and proven in military testing that somewhere around 80% of a cartridge's performance in precision terms is down to bullet design, dimensions and how well they match the barrel's interior, and manufacturing quality / consistency. If the bullets in the GECO ammunition are good and if they match the rifle very well, playing around with COALs may have a small effect on group sizes, but he chances of a major change are so limited that any such change will only show up in averaging a fair number of groups shot under identical conditions off a bench with each group consisting of at least five shots. (That's an issue in itself with normal load development - often people who choose one combination of load factors over another on the basis of one three round group is larger / smaller than another are fooling themselves - even single five round groups usually mislead badly.)
These days for the handloader, there is another issue - the use of 'aggressive' secant ogive bullet designs with very low Rt/R ratio values, also the Berger Hybrid design which IME contrary to Berger's claims can be very fussy indeed as to seating position / jump. Again, that is one reason why Sierra's old 155gn MK #2155 and 168gn big brother are such tolerant designs and work in so many different rifles - a high Rt/R ratio of ~0.9 and 7-calibre radius nose sections make for relatively high drag designs for long-range match shooting, but ones that are very tolerant of different chambers and throats.
Pulling cr*p bullets from cr*p ammunition and replacing them with good quality models ('Mexican reloads') is a very different proposition and often gives excellent results, albeit it is often so much work that it is usually a better use of one's time to use off the shelf components throughout from scratch.
Having said all that, as has been pointed out, if the individual knows what he or she is about in handloading and makes sure that the new COAL doesn't see bullets 'jam-seated' in the lands, there is no safety issue and if people wish to experiment in such ways, well good luck to them - it's their time, ammunition expenditure, and barrels that are being used up.
nun_hunter
Well-Known Member
Just to clarify I do use the OCW method usually but instead of a ladder test at 300m I use the chronograph to get the optimum charge between a flat spot in velocity.
Thanks Laurie, once again your knowledge on all things reloading shows through.
I can assure everyone I will be safe but do have an enquiring mind and like to know why things will/won't work and understand, otherwise how else can I do it right next time.
Thanks Laurie, once again your knowledge on all things reloading shows through.
I can assure everyone I will be safe but do have an enquiring mind and like to know why things will/won't work and understand, otherwise how else can I do it right next time.
I found this while researching and thinking of doing exactly what you proposed. Did you end up doing it, and if so, please share your results.
Thanks
I must confess to having similar thoughts at one time about tweaking the seating depth of factory ammunition, if for no other reason to prove that adjusting seating depth works, but never tried it. As Muir said, I decided that by the time I’d faffed about with expensive factory rounds, I’d be getting a better round by loading it up from scratch. Plus the fact I’d started developing loads by putting the first ten rounds over a chronograph to find the optimal charge weight and then adjusting seating depth, so I can now usually develop an acceptably accurate load within twenty rounds or so, without even having to fire the first ten rounds at a target if circumstances don’t allow.
I would load my own if I could get components and equipment, but they're largely unavailable right now. Even at unobtainium prices. I gave away all my stuff decades ago. I wasn't going to be using it in the forseeable future.
So, tweaking top quality factory ammo, which hopefully will have a low/decent SD, is something I've been considering. I'm slowly acquiring the supplies and equipment for this. I will eventually roll my own from scratch.
I subscribe to the following:
1-Find a load (powder/charge) that gives a low SD. I do have a chrono.
2-Adjust seating depth to see what the rifle and load like best.
<added> I may also use a different bullet due to lead free requirements here in CA.
So, tweaking top quality factory ammo, which hopefully will have a low/decent SD, is something I've been considering. I'm slowly acquiring the supplies and equipment for this. I will eventually roll my own from scratch.
I subscribe to the following:
1-Find a load (powder/charge) that gives a low SD. I do have a chrono.
2-Adjust seating depth to see what the rifle and load like best.
<added> I may also use a different bullet due to lead free requirements here in CA.
While seating deeper is very easy, the other way sure wont be, I for one would never attempt to use the kinetic hammer to pull or partial pull bullets to test them. I have used the kinetic hammer to pull projectiles from a mistake and after that unhappy time purchased the Hornady Cam Lock puller. My thought is handload, do the explorations not mess with perfectly good factory ammo. Best wishes for good shooting.
It’d be interesting to see how you get on. Please report back.
Magnificent 7
Well-Known Member
I've just been through a box of factory ammo and measured them and tbh they were pretty equal what I have done is out of curiosity put them in groups that were the same seating depth I was planning on trying them to see the actual accuracy difference if any as the rifle likes these out the box
Erik Cortina is a successful PRS shooter and has some interesting views on seating depth and chasing the lands etc. In one of his youtube channel vids he recommends adjusting seating depth on factory ammo to accurise it as I recall - well worth a watch anyway.
It'd be a good bet I've watched that video, and others of his as well.
After reading your post I measured some of the good stuff I have. Wouldn't you know it, they're all the same as far as COAL and CBTO (seating depth) <added: within each brand & bullet, not from one to another>.
One of the things I've noticed is that some factory ammo has no crimp, and some does. I'm not going to try anything with ammo that has a crimp.
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