I went to chamber a new 260 Remington on a Yugo 48 Mauser this week and I cut the chamber a little too far.
I used my 308 Win Go and No Go guages and I knew I cut too deep once I stopped and slid the headspace gauges in with no resistance when I closed the bolt. Thinking I might still be within Field Specs, I built a couple of COW loads with some Unique powder to form the cases so I could tell how far I actually cut.
After fire-forming and measuring the blown out cases it looks like this rifle going to have to go back on the bench and be rechambered to 6.5x55 or 6.5x257 Roberts in January.
I'm thinking 6.5x257 due to brass availability as I hate to pay new for 6.5x55 Swede cases when I can use my current 7mm Mauser brass stocks or reform cutdown -06 cases. The dies are more expensive but the price of brass would definitely offset it and the cartridge will do everything the 6.5x55 Swede case can do.
This has been my first error in chambering a barrel, but I hate knowing my perfect record is gone.
As a home gunsmith, at least the customer (me) didn't freak out when he found out.
Bruce