AI Calibers

[tipiguy]

Does the Ackley Improved matter if you are reloading and not filling the case?  For example, I have a 30-30.  When I reload this cartridge the case isn't completely full of powder.  Does the AI do anything additional than just provide more room for powder?

tipiguy

[RonF]

Less case body taper and a sharper shoulder tend to reduce case stretch somewhat, and some folks claim they also reduce back thrust on the standing breech of a Contender, allowing somewhat higher pressures safely.  As far as capacity is concerned, you could use a bit more of a slower powder and possibly gain some velocity.  The gains are usually small unless you bump up the pressure considerably, which may not be a wonderful idea.

RonF

[skb2706]

Besides providing more space for powder most AI conversions I am aware of reduce body taper as well. There is a common belief that in a break action gun that bottle neck cases with minimum body taper greatly reduce back thrust on the breech face. This is supposed to reduce the possibility of frame stretch in those chamberings that are near the upper limits of the gun.
Additional benefits are longer cases life because the cases stretch less via the sharper shoulder angle.
I have an 6mm AI in a Contender and don't have anything to compare it with as far as case life and pressure indicators but I am on my 8th loading on some of the cases and they appear fine.

[KYODE]

more room for powder = more feet per second, if you carefully work up the load.
whether or not your current case is full of powder, has more to do with how bulky that powder is, or what burn rate it has.
one thing about the AI and tcu calibers, they sure have made reloading lot's of fun, and a little more interesting for me. love the 6tcu, and 30-30AI.

[Hopalong7]

I studied Mr Ackley's books rather throughly quite a few years ago and even though most of his thoughts have escaped my feeble memory, I distinctly recall that his number one goal in developing these rounds was to reduce back-thrust on the bolts while enhancing performance.  Keep in mind, at the time two of the more popular calibers were 30-30Win and 250Sav, both chambered in lever action guns and both had much body taper.  GOOD SHOOTIN',  Walt  :grin:

[skb2706]

Ronf - talk about writing the same answer two different ways at the same time. Take care and good shootin !!

[K2]

Ackley's books are an excellent read that is highly recommended to the serious reloader or anyone interested in balistic information.  With diminishing returns you will never turn a 30-30 into a .308 however.  The 30-30AI is one of the best gains to be had from the parent case.  Caselife is a worthwhile goal while more velocity can be gotten too easily by switching calibers.  

I studied Mr Ackley's books rather throughly quite a few years ago and even though most of his thoughts have escaped my feeble memory, I distinctly recall that his number one goal in developing these rounds was to reduce back-thrust on the bolts while enhancing performance.  Keep in mind, at the time two of the more popular calibers were 30-30Win and 250Sav, both chambered in lever action guns and both had much body taper.  GOOD SHOOTIN',  Walt  :grin:

[SD Handgunner]

In one of P.O. Ackley's Handbooks for Shooters and Reloaders there is a chapter on the .30-30 AI Cartridge and it details the experiments he did with the cartridge to determine how much (or should I say how little) rearward thrust the cartridge produced.

In his testing he used a Winchester Model 94 .30-30 Winchester that he had rechambered to .30-30 AI. He started out by unscrewing the barrel one full turn (creating excessive headspace) and fired 5 .30-30 AI Cartridges. The cartridges never moved rearward, no case stretching occurred, but the primer did back out slightly.

Next he unscrewed the barrel another full turn, but had to make an extended firing pin to fire the gun. Again the 5 .30-30 AI Cartridges did not move rearward, showed any signs of case stretching, but again the primers backed out of the case.

In the next test he screwed the barrel back in where it should have been, but this time removed the locking bolts from the action and fired the gun. The only pressure holding the action closed was the pressure he exerted on the finger lever holding the action shut. Again after firing 5 .30-30 AI Cartridges none showed any signs of moving rearward, no case stretching, but again the primers backed out of the case.

Ackley concluded that the .30-30 Ackley Improved case with it's minimum body taper and sharp 40 degree shoulder exerted minimum rearward force against the action.

No this is not word for word, but is a summary of what the article was about. It is very interesting reading IMHO.

SD Handgunner

[skb2706]

good info SD - I don't have any case specs for a 30-30 AI and I am wondering what the typical body taper is from head area to shoulder. My 6mm 30-30 AI has .004-.005" taper ......413" at the head end and .409 at the shoulder and a 40 degree shoulder to neck.
I've read some of the articles that PO wrote but I need to find the time to read up on all of it.

[SD Handgunner]

Here are a couple sites that have cartridge dimension and drawings for the .30-30 AI.

http://stevespages.com/jpg/cd3030ackleyimproved.jpg

http://www.reloadbench.com/cartspec.html

It really is an under-rated cartridge IMHO. I am thinking I am going to have a custom Barrel built in this chambering out of a Stainless-Steel 1 in 14" Twist Blank.

SD Handgunner



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[RonF]

SD - Thanks very much for your paraphrase of P. O. Ackley's experiments to determine back thrust!  I had never heard of his experiments and wondered how he concluded back thrust was reduced, although some understanding of physics would suggest it.  The reduction seems pretty amazing given your description.  Maybe I should have my .30-40 Krag barrel improved!

SKB - Must just be two great minds....  :-D

Y'all take care.

RonF

[tipiguy]

Thanks for all the information!  I think I understand now why people talk favorably about the AI.  

tipiguy