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There has been some debate about Ackleys claim that the Ackley improved case reduced rearward bolt thrust. Today at the range I believe I experienced what he was talking about. I have a load that I've been using in the 30-30 Ackley. It's not really hot and well below the point of hard extraction, but it is an improvement over the standard 30-30 loads. I found that sometimes the lever would pop open slightly with my handloads. Today I tried a load that was just .2 grians more powder. I got a higher point of impact and no lever popping open. I also shot a string of 5 shots with the lighter load and the lever popped open on almost every one. I measured the brass after and the heavier load was only .0003" larger in diameter than the brass from what was my hunting load. The cases were all sized the same and reloaded in the same session. The only difference was the powder charge. I also tried the increased load with CCI BR 2 and CCI mag primers with the same result. Extraction was very easy and the increased load actually shot a little bit tighter groups. This is now my keeper hunting load. I also measured some brass from a previous range session with a load a full grain less powder but the fired brass was the same dimension as the heavier load from todays session. Those were fired earlier in the summer when the temperature was higher. Today the temp was right at the freezing point. I think this may have contributed to the lever popping open on the lighter loads. The heavier load may have made the brass "CLING" to the chamber and thus reduced bolt thrust as PO. Ackley claimed. I don't know what anyone elses take is on this but it worked for me and from what I have seen I am 100% convinced that this load is perfectly safe in MY rifle. I will also add that on this last range session and the other time when I notice that the lever sprung open a bit, I was using brass that I sized more than I usually do. In the one case I had sized the brass with the shell holder contacting the die. I think that may be part of the reason why the fired case didn't "cling" to the chamber and I experienced the bolt thrust issue.
 

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A gunsmith I've worked with quite a bit contrived a way to strike the primer on a round in the chamber of a barrel from a single-shot action, like a Contender or an H&R. He would remove the barrel from the action, place it in the jig he made, and then remotely "trigger" the apparatus to strike the primer. What he found is that some cases went flying out of the back of the barrel...no surprise there! However, he found that some "AI" type rounds gripped the chamber walls so well that they did not exit the chamber at all. Other AI rounds where in-between, meaning they gripped the walls until the shot sequence was almost over, then ejected, but with far less force than the standard-taper cases.

He admits that what he did was not scientific and he had no way to gauge the amount of back-thrust actually being created, but it was very clear in his mind (and mine) that AI'd cases do not put as much pressure against the standing breech of certain actions. YMMV
 

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Large taper cases like the 30-30 and the 30-40 Krag are places to start for AI.

But unfortunately, most AI reloads are never checked for pressure. The question then becomes: What value it the high pressure AI cartridge over the SAME higher pressure standard cartridge?

Billy, I'm curious as to why your bolt is lever is auto opening???????
 

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BillyHill, Has your cases increased in head diameter by .0003 from new or from previously reloaded cartridges? If the head keeps expanding on each load you are over pressure. If it went a total of .0005 and stops you may be okay. This is very unscientific because it depends on chamber measurements and case hardness.

I'm also curious why the lever is popping open. I've seen instances where increasing the powder charge lowers velocity. With the higher point of impact it doesn't seem to be the case with you.
 

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The process of a case gripping the walls of the chamber during powder combustion is called obturation. It's one of the devils that plagued the M-16 in its early days. There is a lengthy article about this phenomenon, written by the military man whom discovered it. Can't remember his name, but he wrote a letter to the top brass about the failures of the spent cases to extract from the chambers during firefights in Vietnam. He referred to his letter as the "letter read 'round the world." Might be able to find it using that in your search string. Add "M16" to it, and your luck should improve. Very interesting reading. The failures to extract got a lot of good men killed. Sad, as well as being something that stokes the fires of rage that the rifle and round were not more thoroughly tested before being fielded. Add to that, the troops were told the rifle was "self-cleaning." Nothing could have been further from the truth, given the powder recipe they used in those days.

I think an Ackley case obturates more than a standard case because it has that small amount of extra cylindrical value. I do not know if Ackley cases are less tapered than a standard case. Maybe, to wipe out the original chamber. Might be why they stick better than standard cases. Opinions and comments welcomed...

The man's name is Richard Culver. Marine. Lots of stuff about his M16 experiences on the 'net...
 

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VERY INTERESTING INDEED. My 257 RRI has very straight sidewalls and a sharp shoulder very similar to Ackley's ideas but just slightly differing measurments to the 257Rbts AI. My cases need a touch more persuading from the extractor to release than all of my other cartridges in the Encore, even the medium loads; just enough drag to be noticeable. Interesting that Ackley thought that this would influence the pressure rearwards.
 

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My situation is a little different as far as the AI thing goes. I have two AI rifles, both of which I inherited from my late father.
One is a single-shot 98 Mauser action originally chambered for 8.5x46R and now chambered for 30-40AI but shooting a .312 diameter bullet. It's a wonderfully accurate rifle and a great round. For hunting purposes I load it to somewhere in between .308 and 30-06 velocities using 50gr of H380 and a 174gr Hornady Interlock bullet. I guess that's closer to '06 speed, but I've never chrono'd it. Sure kills deer and elk though.
The other gun is Richard Marholt drilling with the rifle barrel in .22 Sav HiPower AI. With a good load it shoots 70gr bullet at around 3200fps, according to my dad's notes. I have a few hundred old Sisk 70gr hollowpoints designed back in Ackley's hayday of trying super hot .22s and .17s on big game. I load that round with H380 as well. I've shot 3 whitetails with it (all under 200 yards away) and it dropped them pretty much on the spot with a behind the shoulder shot. For varmint shooting I load regular old 70gr softpoint .228 bullets. I've never shot a deer with those bullets, but a few coyotes and lots of ground squirrels never knew what hit them.
I have little or no problem forming cases for both calibers. I load regular 30-40 and 22 HiPower level loads and go shoot them. I've formed some 22HP cases from 30-30 brass and they worked fine. I was able to find a few boxes of Norma 22HP at a gunshow recently so I'm set for brass. I've never tried forming brass with a reduced load and cream of wheat or any of those methods. I just shoot the factory velocity hand loads and the brass forms great. I've lost a few cases that separated below the shoulder, but that was old brass that I should have annealed in the first place.
Anyway, I really like my AI rifles and find this topic fascinating.

I read the above link with much interest. Great article. I have Ackley's books (my old man knew him and P.O. rechambered the Mauser himself) and read them quite often. As to the old argument about the practicallity of doing the AI thing, well, I didn't get into hunting and shooting (or fishing, for that matter) to be practical. I see it as being no different from building a hot rod or a custom bike. You do that sort of thing because you really enjoy the doing.
 

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I agree with Ackley as he was very knowledgable but he also was daring and his max loads are just that wherein most max loads in the Manuals may be 2 to 3 grs. below actual max, so one has to be very careful with Ackleys max loads as they are too hot in some chambers...

As to the lever poping down, then that load is simply too **** hot and very dangerous, and in such guns as the springy Savage 99 many book loads are two grains too hot....and those loads will drop the lever out of lockup.... Two grains back off isn't much in the velocity table and its safe and the gun will probably shoot better and will kill every bit as good...I see no reason but foolishness to go the max in any caliber, back off a griain or two...

I just worked up some loads in my 375x62 ( a 9.3x62 necked up to .375) and got up to 2506 FPS, then backed off those loads to 2400 FPS..That will make no difference on an elk, moose, Cape buffalo or elephant, in fact it might even be a better killer as it will expend all its energy within the animals body or at least thats the opinnion of many experts...Schools still out on that IMO, but 2400 is a killing number for sure.
 
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