@ 09:20 am (GMT)
Nathan FosterOk, some useful info in that reply.
Yes, brake off please. Especially this design. Test the rifle without the brake. If it shoots well, I want you to go find someone who can dock and clean up the muzzle afterwards to prevent muzzle swelling issues later on.
For now, clean the barrel again, get it back to bare steel with solvent, spiral the chamber, using a bronze brush and harsh solvent, soak, scrub, soak, scrub then clean it all out and get the bore dry and ready for shooting.
Fire about 4 foulers. Use these to get your technique in check.
Then fire your groups, very slow, again, technique in check. I don't want to go over my shooting book details here but will say this- your fingers / knuckles should be white when shooting and sore when finished for the day, like a good honest hard days work. The rest you shoot over needs to have a good cradle shape to it and should be fairly soft. If you have tight sand bags, undo them and pour some sand out, needs to be fairly soft / cradled to suit this rig (also better emulates back packs).
Possibly start back at 70 and go through to 72 for this rifle. Just study behavior at this stage.
You'll need to take this step by step. Can't really go with any "what if its x variable" at this stage.
Guys- please trust me when I say that the thinner the barrel, the more careful we have to be. Threading the muzzle, fluting, all of these things can be highly problematic. I also need you to understand that some of the more funky brake designs can kill a barrel in just a few shots. Try to develop a mindset where you avoid add-ons unless you have no choice (which you cannot discover until after testing / load work). If for example you have a .375 cal rifle, consider optimizing the stock before adding a brake.