Thread: Tight chamber and marks on projectile

Originally Posted by grandpamac

Mystery solved sort of indeed.
I really don't see anything there that would cause hard bolt closing or the marks on the projectiles or the poor accuracy in a different rifle. The search is likely to continue. To me the problem is with the cartridge and not the rifle. To rule the rifle out a good look at the front of the chamber where the case neck ends and the throat starts would be useful to rule out a carbon ring at this point. Are you trimming your cases? If not they may be too long for the chamber, worth checking. My money is still on the loads being too long for the rifles chamber possibly complicated by the cases not being trimmed.
Regards Grandpamac.

Now that the OP has a borescope the actual chambered case length can be viewed.
Take a fired empty case, chamber it and close the bolt. Then, from the muzzle insert the Borescope and run it along until meeting the chamber / throat junction. You will be able to see if the case sits hard against that 90 degree shoulder separating the chamber and throat or whether there is clearance between the case throat and the shoulder. If there is contact it's definitely time for case trimming.
Try several cases this way to check possible variability in case lengths as some may make contact and others may not.

My comment on Carbon Rings. Periodically I scrub them out too. Usually with KG12, a good abrasive for this. I know the rings can affect accuracy so I don't ignore them but over several rifles I don't believe I've ever noticed an obvious accuracy detriment even after the rings have been in place for some time. So, I don't know at what point it matters but my practise of cleaning them out once or twice per year seems OK to me. That would be around every 200 to 400 - 500 rounds approx.