BCG dissection

[LRRPF52]

Pin gauges are not fool proof as some poorly machined bolt tail bores will pass the pin gauge test, yet when viewed by a bore scope and back light, the bore hole can be out of round that an air gauge would find..The same principle for using a taper gauge for the firing pin and cam pin hole with the bolt..

That’s an excellent point, especially if that bolt tail aperture was oval. An oval shaped hole would allow gas leakage where it isn’t supposed to happen.

Bill A. pointed out that obviously-inefficient AR-15s would exhibit blatant gas leakage into the FCG area.

He got a lot of training on this when at UK MoD, including from Eugene Stoner, who came out to visit them and discuss various aspects of the design that most aren’t aware of.

Certain elements of the UK have been using AR-15s since the early 1960s, so they have a long history of armorer and direct support for the AR-15 family of weapons.