Is it possible to use a RRA 9MM upper for 5.56?
I understand there's no gas tube hole, but there are vendors who will drill this. Are there any other modifications that would be necessary to use a 5.56 bolt carrier group in it?
I posted roughly the same question in "AR Discussions" and someone stated there was a limited run of flat-top, slickside uppers that were already drilled? Anyone know of a source?
As I recall they need a cam pin relief cut as well.