First time poster, been tinkering with the long range for a few years now, learned a lot on here in that time. I've been reloading for years and ran into a issues I can't figure out and need some advice. I been helping a buddy with his Sendero 7 Rem mag. I did the initial load development and settled on 68.5 of H1000 with Hornady brass. It would shoot 180 bergers, 10 thou off, .5 moa out to 800 (as far as I took it). It shot well, it did have a little firing pin crater, but the primer still had a good round shoulder. No other signs. I loaded him a bunch up, some new and once fired. I should have told him to keep them separated but I didn't. He calls me and says the bolt is sticking and hard to open. I didn't have any issues during load development. We go and shot it and it was sticking! I loaded up some rounds from 66 grs H1000 up to 68 to see what happens. I switched brass to new nosler for this. Shot one at 66 grs and it took stuck hard. All stock except for muzzle break and trigger. Any ideas?