Purple shoulder
Regular
- Location
- Winnipeg MB
A closed minded view that discounts others intrests as unnecessary? We do have a party like that. Liberal.
Ackley improved can someone explain it
- Thread starter TrevorMack
- Start date
A closed minded view that discounts others intrests as unnecessary? We do have a party like that. Liberal.
No, a person or party who states the key facts in a simple accurate concise statement. We have so much bias, unrelated 'fluff' around some really important issues that it is hard to actually see the truth from the spin. Yup, that also fits the Liberals to a tee.
Candocad.
Gentlemen PO did not make an improved version of every cartridge out there, like we hear today. He only did a few that he felt would gain significantly from the extra case capacity or a reduction in bolt thrust. Although every cartridge that is blown out today and has a 40* shoulder is called an AI version. Cartridges like the 250 Savage were done by Ackley and do gain significantly from the process. Remember when Ackley was doing this, the 25-06 was a wildcat and the 257 Bee hadn't even been a glimmer in Roy's eye yet. He also did the 257 Bob at the same time (more or less) and given the taper in the cases they did in fact, achieve significant velocity gain. The 30-30 was done to increase pressure in the leverguns and reduce bolt thrust, it did this extremely well, but PO wasn't terribly interested in marketing to the big boys at the time so his AI versions were never adopted and legitimized under SAAMI by any of the factories.
I don't know for sure if PO did the 6.5X55 but it is another case that does gain significantly by improving. The 308 family of cases do not gain anything meaningful from it because they are already relatively straight cased and increase in volume is negligible. Ackley's whole research on this topic was driven by looking to reduce bolt thrust and brass flow from greatly tapered cases, it wasn't to make a 257 Bee from a 250 Savage case. Too many people expect miracle velocity gains which they do not get and was never the point of Ackley"s work, what you do get, is a better designed cartridge that will experience minimal brass flow and reduce bolt thrust pressures, again leading to less stretching and what was the whole point of Ackley's research...........longer case life.
I don't know for sure if PO did the 6.5X55 but it is another case that does gain significantly by improving. The 308 family of cases do not gain anything meaningful from it because they are already relatively straight cased and increase in volume is negligible. Ackley's whole research on this topic was driven by looking to reduce bolt thrust and brass flow from greatly tapered cases, it wasn't to make a 257 Bee from a 250 Savage case. Too many people expect miracle velocity gains which they do not get and was never the point of Ackley"s work, what you do get, is a better designed cartridge that will experience minimal brass flow and reduce bolt thrust pressures, again leading to less stretching and what was the whole point of Ackley's research...........longer case life.
- Location
- kingston Ontario
I think that maybe A.I was a real good idea way back when these newer cartridges were not around like posted above .. But today a person can get a 25-06 instead of A.I ing a 257 roberts . and the list goes on ,, there is so many guns out there that almost duplicate another , in stock form that I doubt you have too A.I a gun too duplicate another gun that is already in production
Ackley's believers cling to His inspired words in His Handbooks Part I and II, and In Handbook I in the chapter about Pressure, Ackley tells of his "test" with a Model 94 (pages 140 and following) that has been more than enough proof for generations of believers. I know that this is heresy in some corners, but I'm more than just skeptical about the notion that reducing case taper reduces bolt thrust - I outright don't believe it.
I'm with you. I did a complete FEA analysis of a bolt and cartridge during firing for an unnamed client, and the strength contribution from the brass under tension is a big, fat goose egg. Tiny compared to the steel.
I don't think the bolt thrust issue has anything to do with trying to stengthen the rifle.
A case with straighter sides gains better traction on the sides of the chamber allowing for easier ejection of high pressure loads. From my experience I have found straight cases normally go over book maxes with normal bolt lift. Cases that are tapered not so much.
The reason a straighter-sided cartridge may extract more easily has nothing at all to do with reduced bolt thrust. Once the case has sufficient adhesion to allow the case head to separate (if the action is a springy one), increased adhesion accomplishes nothing. Since the 303 British in a lee Enfield rifle separates at the web with frequency, it seems plain , to me, that the well-tapered 303 case is gripping the chamber wall sufficiently. Otherwise, the head wouldn't come off. This seemed obvious to me when I was fifteen and nothing I have seen in the intervening 52 years would cause me to change my mind. Ackley may well have been no dummy but he was, in this instance, mistaken.
Well Mr. Jumper, I think you are correct and Mr. Ackley had full knowledge of this. Remember, he did that work on a 30-30 in a 94 action, proving that the case gripping the walls of the chamber would virtually take all the backward pressure on the bolt face.
He may have proved that a brass case, at moderate pressure levels, could contain the pressure of firing but he didn't prove anything regarding the ability of a straighter chamber to do this at high pressures. Nor did he prove that the standard case would not. There were too many unreported variables to know for sure what he may or may not have proven. When a standard 30/30 with excessive headspace produces a fired case with a protruding primer, it does so because (a) the standard case gripped the chamber wall and (b) the pressure was insufficient to stretch the brass to re-seat the primer. Once the pressure is high enough to exceed the elastic limit of the brass, case shape becomes meaningless. In a rigid, front locking action, once the pressure is sufficient to deflect the brass by about .0015", any additional pressure is transferred directly to the breech face regardless of case shape.
Ackley cartridges increase velocities because they add case capacity. If the "improvement" increases capacity by 10%, the velocity increase will be on the order of 2.5%, at the same pressure level. Changing the shape of the case makes the case no stronger and certainly does not make the rifle stronger. If a 250 AI can be loaded to 55,000 psi, so can the standard 250-3000. At these levels, the 250-300 will push 100 grain bullets to over 3000 fps and the AI version will do about 75 fps more, at best. The 250 AI is possibly the best of the "improved" cartridges but the huge increases claimed for it are the result of comparisons between the AI, loaded to the nuts, and a mild 250-3000 factory load.
My 303 Epps is an example of an improved cartridge which increases capacity by a solid 10%. With maximum loads, the Epps will gain me about 70 fps with 165 grain bullets. Testing in a Lee Enfield showed a reduced increase simply because the pressure and velocity was, necessarily, held to lower levels. By the way, in these tests the "improved" case most certainly did NOT grip the chamber wall better. In fact, the advantage went to the standard case but I attributed this to a smoother chamber finish when I re-chambered. This is one of those possible "unreported variables" of which I spoke earlier.
Ackley cartridges increase velocities because they add case capacity. If the "improvement" increases capacity by 10%, the velocity increase will be on the order of 2.5%, at the same pressure level. Changing the shape of the case makes the case no stronger and certainly does not make the rifle stronger. If a 250 AI can be loaded to 55,000 psi, so can the standard 250-3000. At these levels, the 250-300 will push 100 grain bullets to over 3000 fps and the AI version will do about 75 fps more, at best. The 250 AI is possibly the best of the "improved" cartridges but the huge increases claimed for it are the result of comparisons between the AI, loaded to the nuts, and a mild 250-3000 factory load.
My 303 Epps is an example of an improved cartridge which increases capacity by a solid 10%. With maximum loads, the Epps will gain me about 70 fps with 165 grain bullets. Testing in a Lee Enfield showed a reduced increase simply because the pressure and velocity was, necessarily, held to lower levels. By the way, in these tests the "improved" case most certainly did NOT grip the chamber wall better. In fact, the advantage went to the standard case but I attributed this to a smoother chamber finish when I re-chambered. This is one of those possible "unreported variables" of which I spoke earlier.
why would a cartridge with more capacity need to be loaded to the nuts to produce more velocity than a standard case?
I also don't think anyone said a straight case will eliminate thrust, just a reduction which for all intents may not even be noticeable, at least to the point where it is obviously arguable.
I maintain that AI ing a standard cartridge is pointless, but wildcatting is another story, then again I could just go by a bigger vanilla factory cartridge hop in my Lada and go shooting
I also don't think anyone said a straight case will eliminate thrust, just a reduction which for all intents may not even be noticeable, at least to the point where it is obviously arguable.
I maintain that AI ing a standard cartridge is pointless, but wildcatting is another story, then again I could just go by a bigger vanilla factory cartridge hop in my Lada and go shooting
- Location
- Southern Vancouver Island
why would a cartridge with more capacity need to be loaded to the nuts to produce more velocity than a standard case?
I also don't think anyone said a straight case will eliminate thrust, just a reduction which for all intents may not even be noticeable, at least to the point where it is obviously arguable.
I maintain that AI ing a standard cartridge is pointless, but wildcatting is another story, then again I could just go by a bigger vanilla factory cartridge hop in my Lada and go shooting
Same reason folks punch out the cubic inches in the motors of their vehicles, to get more jam outta them. Folks just gotta tinker to explore avenues. Hot rodding established and proven hunting/target loads serves no purpose for me, but tons of folk out there still go fer the the gusto regardless.
Most AI to modern cases is not done to increase velocity. It is done to increase case life. At the price of Lapua .260 rem brass an AI shoulder will quickly pay for itself. The extra 75-100 fps is just a bonus. Plus with added cartridge capacity it is possible to get more or slower powder and a bit more pressure so if your not scared to open the bolt with a hammer you can get big velocity increases. Thats hoe P.O. did it.
Case life due to case stretching is the result of reloading technique and die dimensions; not case design. I have reloaded all sorts of cases (243,250, 260, 6.5x55, 30/30, 30/06, 303) multiple times with minimal stretching just by making sure that die and chamber dimensions were well matched. Having said that, there is some evidence that a sharper shoulder will help to reduce the lengthening which occurs when full length re-sizing. As to the extra 100 fps with a 260 AI; dream on.
Lots of good info!
I have AI'd a few cases. I also pretty much red line the pressure in every rifle I reload for. It appears that your cautionary comments about pressures say that you do the opposite. Pressure from a loading manual causes me about as much concern as COAL from a loading manual. I'm not disagreeing with what you are saying, in principle, but every rifle is different, as is every reloader's tolerance for, well, tolerances.
A very tight chambered 243 was once had, with a barrel manufactured from a local smith. It hid pressures very well, and produced significant speeds. I know the pressure was high, as there is no free lunch for velocity, but none of the "typical" symptoms were there. It caused me no concern. No one died, the rifle didn't blow up, no lugs were sheared off, and so on.
Hand over a 260, loaded with book loads, and an AI reamer for same, and then wager the whole works that a 100fps gain wouldn't happen, using typical "reloader" pressure judgement techniques? Dreams would become reality.
There are more powders available than ever before, along with some of the best quality brass an primers ever manufactured, to say that something isn't possible after so many have done it, without knowing the all of the circumstances, IMO, shouldn't be done.
Many respect your experience and opinions based on same here, including myself, and after glancing at your post count, and seeing how many posts you've made on this thread alone, it's obviously something you feel strongly about.
To be clear, I am pro AI, in certain cases, for certain expected and known results. I agree 100% that it isn't for everyone.
R.
I'd be more concerned about the rifle design thats being hot loaded (AI or not) and the brass being used then anything else. Different rifle designs handle case failure differently, some really well, some really poorly.
Everybody is free to do what they want, but loading the brass cases beyond what their failure limit is will always lead to trouble eventually. You can load a 308 to 300Win Mag velocity, or you can buy a 300 Win Mag. One will last you a lifetime, the other will shorten your life.
