I just picked up a new but "blem" 7" barrel for my SW 41. The barrel is D&T for a mount but only had two filler screws installed in the front/ blind holes. The rear two (through) holes won't accept either those filler screws or screws from the Weaver mount I'm trying to install. ( The screws won't even start). I'm thinking I may have to chase those holes with a tap to proceed. Can any one tell me what size screw is used in those locations? Anyone else have this issue? A search turned up nothing.

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Dave