308 sholder modification question....

[Just1Mor]

so does anyone know what you would get out of blowing the sholder out to a 40degree angle as opposed to the 20 degree of current????

[rtracy2001]

Increased case capacity, and a cartridge that is commonly known as the 308 Ackley improved, even though P.O. Ackley never did modify the 308 in that way. (The name comes from Ackley's use of a 40 degree shoulder on other cartidges.)

[nanuk]

would the capacity gain be worth the hassle?

if you just reamed the chamber, you could not just fire factory 308's as the headspace may be an issue.

I"ve read that a 308 is just about as fat as you can get and still get easy feeding.

if you do just ream the chamber, perhaps you would have better luck sizing down, say 280 brass in a 308 die to a crush fit in the 40* chamber for fireforming?

[B R Shooter]

A 308 ACK is doable, but you will need special dies. You could go with a 30/284, or a 30-06 if you need more umph.

However, if you do want to blow it out, the Ackley method is to reamer .004" short of headspace. That way, when you chamber a round, the brass will be pinched at the shoulder/neck junction, and it will fire. The .004" is a WAG in the fact that different brass makers can be thinner or thicker, but it works most of the time.

Now a true wildcatter won't pay nay attention to that crush fit thing, because there are many ways to fireform brass without it. Simply seating a bullet long where it seats well into the lands closing the bolt does well. Or, you can neck up the bras a caliber or two, then neck it back down just enough to chamber against the false shoulder in the neck.

Oh, one way around the special dies here, is to get 243 ACK dies (which is fairly common) and just open them up to take the 30 caliber. hat's REAL easy when using bushing dies.

[Just1Mor]

well coming up with the brass would not be the issue, i have made 308 out of 30-06 cases and 303 brit from 30-40 krag, but the question i would be wondering is what increases in performance would you get out of the improved case?

I have been told and heard about feed problems, but the concept for the increased shoulder angle is to make a more efficient round. So i was looking for fps differences and most likely a full burn of powder with decreases kick. It was going to be an auto loader so there were many daughts of if it would be worth it. But i have never talked to anyone that has done it.

you would think you could get 06 performance out of the 308 improved. any thoughts

[S.R.Custom]

As has been mentioned, the .308 is almost a straight case as it is. You get a negligible increase in performance-- less than 5%. It's not worth the significant increase in hassle that comes about as a result of the conversion.

[wmitty]

Isn't the rule of thumb about a 4% increase in case volume to obtain a 1% increase in velocity ( assuming pressure is the same for both standard and "improved" rounds). I seriously doubt the velocity increase for the case modification you describe would be detectable if it is used in a gas operated autoloader because of the faster burning rate powders you'd need to use to keep gas port pressure acceptable for proper function of the action.

If I am wrong on the rule of thumb; someone set me strait!

[nanuk]

wmitty: I think that rule of 4 is something Barsness came up with. according to him, it holds very well

[B R Shooter]

Ack improved cases had varying results/improvements. From memory, the 280 ACK had almost no increase or improvement, where the 250 Savage ACK responded the best. There was one other case that did very well, but I can't recall it right now. I know many really like the 6.5x55ACK.

For the 308, don't know. The 243ACK is popular too.

[82nd airborne]

I have a barrel that is supposedly done by ackley himself, and is stamped as such. It is by far the worst barrel work I have seen! it is a 6.5 jap, improved and necked up to 7mm.

[felix]

Do NOT Acklify the standard 308 case, especially for low level pressure applications. ... felix

[waksupi]

It is a waste of time to mess with the capacity on a .308 based case. It is pretty much perfect for whatever you want to put in it.
I can see no benefit at all to improve a case to be used for cast bullets in any instance.

[sundog]

Just1mor, increase in performance? It's called 30-06. Now, if you want to do it just because you can, go ahead, and then report back. Sounds like a good way to mess up a perfectly good .308 chamber.

[Just1Mor]

I had just wondered why that was the only round that hadnt been wildcatted. But i was reading a page on a german guy who did and from what his remarks were, it sounded like it was benificial. if i remember right, he was using the same amount of power with a 150 gr fmj and was pushing 3200. But that is entirely heresay.

[no34570]

Hi Fellas
I have always been a follower of the Ackley Improved fraternity,I had a 22.250AI,now that was a great gun,alas to small for what I was hunting,so now I have a 243 AI,what a ball biter,brass is not needing trimming as much,I'm getting more velocity(I hope,no chronograph) I can still use the old .243Win ammo I am wrapped in it.

I was thinking of getting my .307Win L/A getting the shoulder reamed for the Ackley version of the 308,that is all the 307 is,but with a rim and a bit thicker brass walls.
Anyhoo.......I have a chart that shows Ackleys Improved cases to the standard,with % for you to have a look,it is in PDF

hope this helps some of you out.:mrgreen:

Cheers
no34570

[Just1Mor]

thanks for that download, My personal thought is that if i can get any bettter performance at a cost that is not that much and longer brass life, i think its worth it to try. At least i would have my own info on what a 308 improved would be.

[no34570]

thanks for that download, My personal thought is that if i can get any bettter performance at a cost that is not that much and longer brass life, i think its worth it to try. At least i would have my own info on what a 308 improved would be.

You are quite welcome mate ;)

[rtracy2001]

I had just wondered why that was the only round that hadnt been wildcatted. But i was reading a page on a german guy who did and from what his remarks were, it sounded like it was benificial. if i remember right, he was using the same amount of power with a 150 gr fmj and was pushing 3200. But that is entirely heresay.


While I cannot speak as to the velocity claims, I would point out that generally speaking, if you increase the case capacity, you will need to use more powder to reach the same velocity as compared to an unimproved case. Not a very pleasant thought if the "sweet spot" for accuracy falls at less than max velocity.

another thing to consider is the point of diminishing returns. At least one of my reloading manual speaks to the "failure" of the 30-06 AI. It claims that the 30-06 AI provided some increase in performance over the standard '06, but for the most part it just took more powder to do the same thing. The data tables published in that manual show a 10% increase in powder for a 2% increase in velocity. That is only one manual though.

Not trying to discourage anyone, but you should know the risks.

[S.R.Custom]

...another thing to consider is the point of diminishing returns...

True dat. If you look at the chart our friend #34570 so graciously provided, you see --generally speaking-- the higher the pressure the parent round, the less effective the Acklification (Acklization?).

I'm currently working on a .223AI project where the 'sweet spot' for pressure/accuracy on the stock chamber was at brass yield minus 6%, or somewhere in the neighborhood of 57-62 KPSI. After Acklification, I picked up 100 useable fps. That's 3%. BFD is what I'm thinking...

But then again, Ackley himself hated the .223. ;)

[felix]

Just1Mor, if you want to really do something different, leave the taper alone (or not) and install Weatherby corners on the neck joints while making a 35 or 40 degree slope (or not). Those corners would/should break up any malicious wave fronts which are common with reduced loads by offering a more irregular surface for wave bounce. Also, 50K-65K pressure will not have a propensity to generate a damaging donut situation either. ... felix

[Willbird]

Well we have a LOT more powders to choose from today than they did in yesteryear...some cases that showed a dramatic improvement may have been just slightly too small to use the next slower powder. So being able to go to a slower powder may have produced what seemed like "magic" results. The 22-2250 AI is a far zippier beast than a 22-250. Just look up "220 swift" in the loading manual and you are looking at 22-250AI loads and velocities...with never having to trim brass.

Along with blowing the shoulder out Ackley also reduced case body taper to about .004. The two things together in a strong gun let you run a LOT more pressure with a given case life and needing to be trimmed.

If you do it the reverse way and take the velocity you can get with 22-250, and design a case with 40 degree shoulder and .004 taper that will make the SAME velocity (at a higher pressure)...and equal case life you would end up burning less powder, the 22BR sort of fills that role nicely.

With a rimmed case you can go the route of another popular case capacity increaser and move the shoulder location. Rocky Gibbs was his name. Then there was Mashburn who did sort of the same things.

Bill

[Just1Mor]

i have heard of large bore reloading blowing up with light loads of slow burning powder, i think it would be wise to start with a test barrel with me not near by.

[Just1Mor]

Sorry i have a copy of both of Ackleys book and have read them 3 time or so. but they never had the stuff we have now.

[Just1Mor]

what about a shortend 308 case to compesate for the increase of the shoulder instead of just blowing the case forward? any thoughts???