Quote:
I will give it a try.
Sometime in the past there was a gent named P.O. Ackley who was involved in wildcatting existing cartridges. His modus operandi was generally reaming out the chamber of many different cartridges to lengthen, remove some taper, and make a sharper shoulder, Usually 40 degrees instead of the standard 23 or whatever.
He made claims of 2 to 3 hundred fps improvement over the parent cartridge. Usually it was more like 50 to 100 fps improvement.
Normally the parent cartridge could still be fired in the improved chamber which in turn "fire formed" the brass to the new dimensions.
PO never lengthened the chamber of any cartridge. In fact, a true AI chamber can only be cut after a standard cartridge barrel has been set back one or two threads.
The reason for this is that the head space dimension for an AI cartridge is actually shorter than the standard cartridge.
If you just ream a factory chamber out completely with an AI reamer, you're going to have an AI chamber with excessive head space. As a result you'll believe that all AI cartridges have to have bullets jammed into the barrel lands to fire form cases, and you'll constantly complain that you are having case separation problems with your AI rifle, etc.
Neither of those needs/problems exits with a properly cut AI chamber. And.....You will actually experience a slight tight feeling or "crush" closure on a bolt when chambering a factory round in a properly cut AI chamber.
And PO never advertised increased velocity as a primary reason to improve a cartridge. He was more interested in controlling bolt thrust and cartridge length growth with his designs in a time when a lot of suspect (in terms of strength) liberated military rifle actions were being used for sporter conversions than he was with building "hot rod" cartridges. Others grabbed the "more velocity" mantra and ran with it much more than he ever did...
-BCB
