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268 Posts
Discussion Starter #1
Hello from Scotland~

I have seen various calibres mentioned that have been "Ackley improved" which i believe to be basically increasing the shoulder angle of the parent case to allow for a greater volume of powder.............

My question to those who know , is how much "improvement" is there ?

For example# what effect could i expect from my .308 M-bolt IF i got it "AI" ?? Is it really worth the expense ?? What sort of " increase " in volume would result ?

I was talking to a target guy whos using i believe VV N540 or something similar in .308 target rifles they seem to like it due to the fact the case can be filled up without dangerous pressures yet yeilding top notch bullet speed.

This being the case would the use of such powders "squeeze" the maximum improvement from a .308AI ???

Im only a hunter so the technical stuff goes over my head sometimes but how does it sound to you ??

Regards Englander


126 Posts
Parker O. Ackley developed a large number of "improved" cartridges over a goodly number of years. Some were good, a few very good and some not worthwhile, according to Ackley. The amount of improvement depended largely upon the amount of taper that could be removed from the case, giving increased capacity. leaving sufficient for extraction of the case. If the case was already near ideal capacity for the bore size, then the increase would be slight. If it was below the ideal capacity, then the increase would be substantial. In addition, Ackley worked carefully with individual rifles and would work to find the maximum loads, which might not be suitable in a different chamber or barrel.

A number of other advantages were demonstrated for the improved cartridges, including longer case life and less stretch of the cases. Some people swore by them; others swore at them. They require extra work to form and reload for, with small increases at times. Some simply want something different.

At best you might get a 10% increase in velocity, but 5% was more common. And, today, with some of the new powders, you may get those increases with cautious reloading and no "improvement" in the case. It is difficult to generalize, but fun to discuss.

Hope this helps.


The Hog Whisperer (Administrator)
36,225 Posts
You can get 'some' improvement, but .308 is already pretty straight. Not much gain in this one.

Some improvements of cases with a lot of taper gain a lot, especially if the shoulder is moved forward (.30-30 AI). Moving the shoulder forward isn't too hard with rimmed or belted cases, it should be done cautiously with rimless cases.

The real problem that you will run into is lack of pressure-tested data from the powder manufacturers.

Rule of thumb is that velocity potential increases at about one fourth of the increase in case capacity, if pressures are held to the same level.

Considering the cost of forming dies, time & components spent making cases, etc., it is probably more cost-effective to just put a longer barrel on the gun, and figure about 25-30fps increase per inch of extra barrel length.
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