Originally Posted by B23
I was talking to Dave Kiff @PTG afew months ago about the reamer print I was using. I told him I've read that anything more than a 37.5degree shoulder angle was counter productive. Now I'm not sure if I used the correct technical terms but Mr. Kiff told me he will build anything but that he wouldn't recommend improving anything over 37.5 degree shoulder angle.
If you read PO Ackleys Books you start to understand why he went to 40o shoulders.
Back when he was doing all of his experiments he did not have all of the wonderful cases
we have today and he was attempting to up the velocity in each case without going to
a larger case or action.
He discovered that 40o's was an absolute MAX and that any more gave you to many
problems and no gain in total performance.
Ackley himself agrees that somewhere arround 35o is optimal and all you gain is volume
(But not much).
Dave Kiff is correct and 35o to 37.5 is all one needs. And with today's larger cases even
that is not nessary except when shooting the largest bullets, a little more case capacity
will allow the use of a slower powder.
So depending on the use of a rifle the shoulder angle's will vary (Some of the old dangerous
game rifles had shoulder angles as low as 7o to 12o for ease of feeding and extraction)
The Newer cases start at 25o and go up and most are arround 30o.
Brass seams to hold up well at 35o. But at 40o fire forming can be problematic at times.
So my recommendations would be to stay with the 30o shoulder. Unless you are willing to
deal with the extra work of a steeper shoulder angle and the cost to gain some velocity.
If you want a wild cat then go with 35o to 37.5 if not stay with the 30o shoulder.
Just my opinion
J E CUSTOM