First off, I have a model 10. IDK that it will ultimately be important, but FWIW I make mention of it.

I took advantage of the recent Numrich sale and got a .300 RUM barrel for fun and to use as a test for nitriding. Going in, I knew the round was far too long for anything other than single-loading. Fine; not a problem. And I already have a complete model 10 magnum bolt assembly awaiting my 7 WSM barrel, so I was GTG on that. As it so happened, I got the barrel, headspace gauges and a box of ammo today and of course went straight to it.

When headspacing, I inserted the Go gauge into the bolt head and kept it straight as it chambered. Then I ejected it and inserted the No-Go gauge into the bolt head, keeping it straight as it centered. Bolt won't close, as expected. so far, so good. Repeat the process a couple more times for reassurance; all is well. So, I try to chamber a round; naturally, I have to insert it at an angle. The bolt won't close, and it's obvious the rim has not set into the bolt head. I try slipping the Go gauge in the chamber and closing the bolt. Again, it will not seat the rim into the bolt face.

Any ideas why the rim won't become captive in the bolt head if it's not retained while inserting the round? It is a PITA to insert a cartridge into the head and with my fingers guide it into the chamber, but if I do, it seems to work fine as far as retaining it while ejecting. Thanks for any help.