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Thread: Ackley Improved Chamberings Etc.

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    Default Ackley Improved Chamberings Etc.

    My dad and uncle were very much into Ackley's system. I grew up shooting an AI 25-06 as well as a .35 AI. Read on an old thread that u could fire factory loads out of these and it raised a question for me as my dad said that was never to be done!! We always used factory .270 Rem cases but also had a "hot" load to fire form the new brass and then a different load after that. Anybody else out there ever hear of necking down .375 HH Mag brass to a .35 AI? Would love to hear any info or thoughts on this.

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    The Ackley improved chamberings were specifically made to offer better velocity through the addition of more powder space for any given caliber. The degree of "improved" powder space will vary from cartridge to cartridge but in any case it does add room for powder. Another specific about Ackleys chambers was that all would allow safely firing factory ammo of the parent caliber in these Ackley chambers. However, there is a caveat. Chambers must be made with the same headspace as the original parent caliber. This requires the barrel be removed and set back when Ackley chambered. I've run into more AI chamberings that were not so done than those that have. However these rarely have so much excessive headspace that would cause a problem. A chamber cast would tell what we need to know and I usually do this before loading for any unknown rifle in any non standard or wildcat chambering.

    Ackley Improved chambers will all have common traits. Forty degree shoulders and minimum body taper. Maintaining the headspace results in a slightly longer neck. The 25-06 didn't have factory brass until the 1980's and most folks used 270 for the 25-06 and the 6.5-06 brass. As for the fireforming load that would be a hot load for a standard caliber probably but in the AI chamber it would be more normal. If you have some brass before and after fireformed you can see the difference, it is quite obvious.

    Now about the 35 AI from 375 H&H. That is the 35 G&H from the rifle firm of Griffin & Howe, the cartridge originally was a 35 G&H magnum and formed from 375 H&H brass. In it's original version it would be 2.765" long and have a 23 degree shoulder, .495" body at the shoulder and .341" of neck. If it is AI'ed it would have a forty degree shoulder and minimum taper, larger diameter at the shoulder. Many AI cartridges were never made by Parker Ackley but anything that is reformed to that characteristic forty degree shoulder is called AI even though it was made after his death.

    As with any improved cartridge, there will be many detractors and most of us question the reasoning today for such a modification. That isn't the issue, we don't need to be practical with these endeavors, it is just part of the experimentation of the hobby. There is no set rule and little agreement to what extent these AI's will improve the ballistics. And many of the experimentors will overload the case to get rather impressive ballistics through their chronograph. Others will simply believe they have an impressive caliber with anything that is AI'ed. Neither method is satisfactory to me. I have Oehler m43, strain gage pressure tested an even dozen AI'ed calibers. I have some good data, none of it is worthy of much bragging ballisticly but I do have three calibers that are AI'ed and they are such great guns with very good ballistics and extremely accurate, nothing else really matters.
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    I've had one ackley, a 35 whelen. The "smith" that did the chambering did a poor job, so that somewhat tainted my view of the chambering.

    I'll say the upside of the ackley is that the nearly straight case and steep shoulder reduce the amount a case grows on sizing. If you're going with a chambering that you will be shooting alot, and thus want to reduce the amount of work reloading, then the ackley is a benefit. I know many folks who use the 223 AI primarily because it has eliminated the need to trim brass. Also their custom chambers are tighter than factory, which reduces brass work.

    As to actualy velocity gains from the improved chamber, my opinion is that you will typically gain all of 50 fps from the ackley chamber running the same pressures as the parent case. Many ackley loaders will claim 100-150 fps gains, but IMHO those gains are due to running high pressures in addition the modest gain in case capacity. A tight custom chamber and the ackley case will tend to keep pressure signs from showing up until one is running into 70,000 + psi.

    The downside of the ackley is you will need custom dies, which are expensive, you have to fireform brass, which is expensive and time consuming, and the straighter case often doesn't feed as smoothly as the more tapered parent chambering.

    As to a 375 H&H necked down to 35 and improved, I never read about PO Ackley creating such a round. There is a round developed by Layne Simpson called the 358 Shooting Times Alaskan (358 STA) that is a 35 caliber round based on a full length 375 H&H case with a straightened body. It's actually the 8mm rem mag necked up. It is a very impressive round 250 gr @2900-3000 fps depending on barrel length. If you want to reach out and deliver a whollop, it'll do the deed. Of course it'll deliver to your shoulder as well

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    Default A I

    The major benefit from an Ackley Improved round (besides velocity) is reduced bolt thrust. The reduction in case taper reduces bolt thrust by reducing the wedgeing effect of the case.
    The best of all Ackley Improved rounds (most improved) was the 250 Savage AI, followed closely by the 257 Roberts AI.
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    Default a little more on the .35 ackley

    Talked to my dad about this gun and he said that it was based upon a .358 Norma, but did make brass for it by necking/trimming .375 HH Mag cart.

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