XP-100 7br loading problem -?

[ol mike]

Bought Lapua 6br brass -expanded it to .284" w/an expander mandrel from Sinclair -checked each case to make sure it chambered right -they did.
So today I primed them -loaded two with 26gr of H-322 -seated a 139gr interlock -checked to see if they would chamber correctly -would not chamber .
I checked the outside neck diameter of a couple of non loaded cases -then measured the loaded ones -about 1K bigger when loaded .
Turned the bolt w/a bit of force and the round chambered but quite tightly -when opening the bolt it makes a "pop" at the end of the bolt opening cycle.

I looked for marks on the case and bullet finally finding a ring at the neck shoulder junction.
It's an extruding little ring that is not there before I chamber the round -it seems to make the ring after I worked the bolt up and down .
I did this to try and find a mark on the brass.
Any ideas why this is happening ?

Thanks Mike

[Lefty7mmstw]

you are a bit tight on your loaded neck dimension and should probably ream a thou or so off of your necks for a bit of clearance. Your chamber is nice and "square" at the neck/shoulder junction and you are rubbing there.

[TOM H]

There was little bit of different between the Rem 7BR brass Rem 6BR brass. the 7br chamber if in XP-pistol is shorter. Nolser and Speer manual have the spec on the 7Br case you may try resize in FL die and see if that helps. the old rem 7 br brass was pretty good stuff and I used that for my 22br.

Do you have any 7br brass it should match what's in the manual I listed if your not the original owner when that 7br brass dried up someone could of tried rechamber to the 6br case.

[ol mike]

Thanks for the help guys.
I'll be getting an outside neck turning set up soon.
I guess once I have everything there is to have for reloading -I won't have to ask questions anymore..
Thanks -Mike