mammynun -
I bought some precision polished drill rod from McMaster Carr to use in my 5.45 to check the 24mm concentricity. Unfortunately none of them are consistent. Some are OK to use an adapter on the FSB, and some aren't. Of course the ones I really wanted to use an adapter on were borderline. So I made the decision that any rifle I want to put a suppressor on will just need some 'custom' work.
both of the AKs I have that take suppressors (1 - 5.56, 1-5.45) have 1/2x28 threads cut into the barrel *in front* of the FSB. The ak-74 above has the FSB pushed back about a 1/2" and pinned (easy to do with a new barrel), and the SLR-106UR SBR has an extra 1/2" of barrel left in front of the FSB that I threaded 1/2x28. All the threads were cut on a lathe and are concentric to the bore, and the front of the FSB was faced off to be square to the threads to give the suppressor sometime to seat against. The muzzle brake for both screw onto the FSB as normal, and cover (hide) the extra threads.
I bought some precision polished drill rod from McMaster Carr to use in my 5.45 to check the 24mm concentricity. Unfortunately none of them are consistent. Some are OK to use an adapter on the FSB, and some aren't. Of course the ones I really wanted to use an adapter on were borderline. So I made the decision that any rifle I want to put a suppressor on will just need some 'custom' work.
both of the AKs I have that take suppressors (1 - 5.56, 1-5.45) have 1/2x28 threads cut into the barrel *in front* of the FSB. The ak-74 above has the FSB pushed back about a 1/2" and pinned (easy to do with a new barrel), and the SLR-106UR SBR has an extra 1/2" of barrel left in front of the FSB that I threaded 1/2x28. All the threads were cut on a lathe and are concentric to the bore, and the front of the FSB was faced off to be square to the threads to give the suppressor sometime to seat against. The muzzle brake for both screw onto the FSB as normal, and cover (hide) the extra threads.