i picked up a nice crf m70 in 7stw....it has a KDF muzzle brake on it, and i'm having some accuracy issues.... i'm shooting factory remington 140gr sp's.... i put a simmons 6.5-20 scope on it, with leupold rings/bases... i bore-sighted it as i always do a new scope, pulled the bolt, looked thru the barrel at a 9" paperplate....shooting off of sandbags, i shot a 5' group at 50 yds.... i was thinking it might have been the scope, so i put an older weaver 3-9 on it and stuck it back in the safe.... i have another rifle with a muzzle brake on it, but i'm not a big fan on smaller caliber rifles... so i was seriously considering have tip burns cut this 1 off...today i pulled the rifle out of the safe and found that the brake was loose on the barrel... which leads me to belive that it might be the accuracy problem....i looked in the brake and i can see witness marks, that look like maybe a bullet was hitting it.... so my questions are::: how tight should the brake be on the barrel????... any lube on the threads???....what is the thread size/pitch????... can i get a cap for the barrel when im not using the brake???.... i measured the inside of the brake and its .297, which out to be big enough to get a 7mm bullet thru.... im planning on shooting again this weekend, so i'll shoot with a different scope, and without a brake....

First, there should be no marks made by the bullets. clean the brake and lube the threads. reinstall the brake and insert a deltronic pin or indexing pin into the bore through the brake. A 7mm bore is .284" There should be .020" clearance between the pin and the brake. That is roughly .010 on all sides. If there is less or no clearance the brake may be the issue. Remove the brake and shoot the rifle and see how it shoots. There could be a crown issue. 7mm STW are hard on barrels and your barrel may be shot out.

Good Luck
Longshot