Pinion size question

[Shake Rag]

I have a Colt H-bar with the large pinion hole. I would like to add an Adams upper in 5.45x39. This upper has the small hole. Forgive this newby question, but is there an adapter or does the small hole have to be drilled to fit the H-bar lower? :help:

TIA, Shake Rag

[imarangemaster]

There are adapters. The small hole upper on a large hole lower uses an off-set screw gizmo. The large hole upper on a small hole lower uses a bushing. Try Model One or MA parts.