Any idea what could be causing this?

[JEVapa]

In the vid he said something key...out of spec lowers. If you have a known spec lower, like a Colt or FN, you can mic the retainer hole and check. @SPDguns might have that number too.

 

[MilitantBEEMER]

In the vid he said something key...out of spec lowers. If you have a known spec lower, like a Colt or FN, you can mic the retainer hole and check. @SPDguns might have that number too.

It is a stag lower. Mated to a left hand stag upper and stag BCG

 

[THE JOKER]

Only seen black airsoft buffers. Use the real deal.

Palmetto state has some black anodized buffers.