Gas Piston Upper

[gfl216 226]

I have an older Bushmaster M4 A2 that I bought probably 15 years ago .I was wondering if I was to buy a complete gas piston upper would I have to replace the buffer in the lower or any other parts to make it function or would the existing parts work with the new upper?  

[Vlad G 345]

Ask the people selling the upper? Most of the time it should be fine but there are no "standard" gas piston uppers so you are best checking with the maker

[MartyZ 692]

The only thing you would need to change is the BCG, that is if you don't buy it with the upper. The BCG for piston does not use a gas key but instead has a flat portion for the piston to push against.

[Screwball 483]

I can take my Spikes upper with AA piston off my one lower, and swap with my D/I FDE rifle (one has a carbine buffer, other a rifle buffer) with no issue. Can even mount both on my .45 D/I lower, as it runs a standard carbine buffer.

 

Cannot really swap BGCs or specifically bolts, being my piston doesn't have gas rings on the bolt.

[MartyZ 692]

If you have a complete piston upper, with BCG, then you can put it on any lower.

[gfl216 226]

What dose BCG stand for?

[MidwestPX 172]

What dose BCG stand for?

Bolt Carrier Group