I believe the 308 and the 260 use the same headspace gauge. But check with Dave to be sure....
Please let me know if someone with one of these guns sets up on the bench next to me............God help us!I have a friend of mine that also does a little gun work, and I know in speaking with some of his clientele that they have had case head separations when fire forming because he does not set the barrel back on an Ackley.
My point being it doesn't say "308 AI" or similar. I am to believe this is a standard 308 Winchester go gage. I already have one of those!
The 308 go gauge becomes the 260ackley no go gauge .
You still in a 260 ackley improved go gauge unless it is a 308 ackley improved go gauge,which is interchangeable as the 260 ackley go gauge .
In 2002 I built a 257 Roberts Ackley Improved on a VZ24 action with a Lothar Walther light varmint CM barrel blank. I cut the threads and the chamber.
I used a piece of 257 Roberts brass new out of the bag as a go gauge.
I was never able to form in one step. The case would separate .1" behind the shoulder.
What was happening was the firing pin would push the case forward. The angle of the chamber shoulder was different the the angle of the case shoulder, so the only point of contact was a ring of contact at the base of the neck of the case. That sharp ring would cut into the case .004" before the primer went off.
I learned to form a partial shoulder with 10 gr pistol powder and the rest of the case filled with Cream of Wheat. Then on the next firing I used a bullet and got a full shoulder formed.
Other rifles I subsequently built with that reamer, I set the head space .004" tighter, and they form a case on the first firing with no case stretching separations.