The gun is a semi custom (stock barrel) build with a long Accutrigger Action that was trued and timed. It is chambered in 7mm WSM. The chamber has always been tight and all reloads have to be full length resized. With approximately 250 rounds on the gun, I was at the range shooting when suddenly I could no longer chamber a round (the bolt handle would not close all the way). When I got home I examined the gun carefully and tried to chamber a Go Gauge, the bolt would not close on the Go gauge. It would close on the gauge previously.

I have cleaned the gun, making sure there is no carbon build up in chamber. I have disassembled and cleaned the bolt. The only thing I did not disassemble on the bolt is the the spring loaded pin on the bolt face, but it seems to be functioning properly. The bolt still will not close on the Go gauge. The barrel nut does not appear to be loose and I can’t imagine how the headspace could have been decreased. Does anyone have any ideas what could be going on?
Thanks for your help.