I just finished chambering & installing a Keystone Accuracy contoured GM blank on my Rim-X. I'd purchased a couple of 1.20" dia straight cylinder CM blanks about a year ago, and finally got around to sending them to John at Keystone to have them contoured on his cnc lathe. I went with his Palma sport contour, which is essentially a heavy Palma with a large radius transition from the shank, instead of the normal Palma double taper transition. I had him do one of the GM blanks with the shank fully machined/threaded for the Rim-X, but not chambered, while the other one is just the Palma sport contour.
I went with the blank with John's cnc-produced Rim-X shank, and used my Eley EPS reamer to cut the chamber, then finished it at 23.5" with an 11* crown, and no threading. First time out, it shot OK group-wise, but I kept getting rounds knocked out of the extractor as I was closing the bolt, which requires opening the bolt and picking the loaded round out of the bbl - would estimate this was happening about 30% of the time. Since I'd had very few issues of this happening after I'd adjusted the mag latch height to work with the previous bbl, I thought perhaps the problem was connected with how tight the body of the EPS chamber is, and decided to pull the bbl and run my JGS carbide Win 52D Match reamer into the EPS chamber and see if that would solve the issue. The 52D chamber is .2278" at the rear, and tapers to .225" at the front, while the EPS is .2252" straight, with no taper to the front. The EPS is also .020" longer than the 52D, with a length of .600" compared to .580", and since they both have a 2* leade angle, the 52D reamer didn't re-cut the existing EPS leade. I simply re-cut the chamber by hand while the bbl was still in the bbl vise after removing the action, using Mobil Sigma cutting oil. I took three passes, removing the reamer and blowing the chips & oil off after each pass - it was a little surprising how much metal was cut, but it went very smoothly and required very little effort. I sprayed some brake & parts cleaner down the bore after finishing, then blew it out with compressed air, hoping to avoid pushing any sharp chips through the bore when I wiped it out with patches afterwards.
Whether my diagnosis of the problem was correct or not, re-cutting the chamber evidently fixed it, as I ran at least 50rds through the rifle without another single issue. I was also pleased with the accuracy, though oddly enough, it shot best with an exceptional lot of SK Std+ & SK LR Match, neither of which have ever shot as good in any of my other custom barreled rifles. Next time out, I plan to try some Eley Match in it, as the black box Eley shoots better in both of my CMP 52Ds than any of the SK/Lapua that I've shot in them.