Guys I would really appreciate some help with this because it’s been a real head scratcher for me. I had a win model 70 stainless featherweight 300 WSM rebarreled to 6.5 WSM. Kept it 24” and the same barrel contour. I’ve been necking 270 WSM brass down and I do have to neck turn as the reamer my smith used is kinda tight (brass necks measure .2978 after firing). I started the process of working up some loads for it and after a few outings decided that my gunsmith did not throat it out to the length I wanted. I took it back and he graciously agreed to throat it out further but he wanted me to make some “dummy” rounds the length I wanted. I gave him the rounds and he throated it out. When I picked it up the dummy rounds chambered with no resistance and I was able to set my bullets (140 Berger elite hunters) out to just under my magazine length. Perfect. I have shot it approx 50 times since then and now the dummy rounds will no longer chamber and I had to decrease my OAL by 0.035 to get it to chamber with no resistance The barrel is clean. The throat area is clean and I have looked at everything I know to do. I thought it had to be something I was doing or maybe I had somehow made a mistake. However my dummy rounds that I provided the gunsmith no longer fit and they haven’t changed. The witness marks left on the bullets that meet resistance don’t show the lands. They have an even Mark all the way around like the lead in is to tight. What in the world could cause this. 50 rounds and now I have to back OAL back .035? Any help would be appreciated. I would hate to carry this back to the same smith that has already did work on this a second time already and it something that is my bad. Oh also accuracy was excellent the first 20 or so shots after getting it throated out and then fell off but not that bad (from sub moa to 1.5”) however I changed to a different powder about mid way through the session so it may be nothing.