magnum, look VERY carefully at kytowboater's closeup of the barrel and receiver. His barrel extension has M4 feed ramps (deep cut, not like rifle ramps). And his receiver also has M4 ramps as you'd expect. If your barrel has M4 feed ramps it would be best to get M4 ramps on the new receiver but not absolutely necessary. Now if your barrel has standard rifle ramps, DO NOT get a receiver with M4 ramps, as JonM said.
I guess BM doesn't cut M4 ramps into the composite receiver so who knows what ramps their barrel has.
Well I remachined yhm barrel nut and rethread it so I won't need a new receiver now...issue I had was the barrel nut from BM was bigger than yhm so I couldn't put free float on that I bought but now with the yhm barrel nut machined to bm spec on composite receive...fits like a glove...thanks for all the help and knowledge for future builds