rssc, with all due respect to the other posters, I would suggest you start with a Colt lower. And it's not because I drink the pony koolaid, it's because all of my FA learning experience was with factory Colt full-autos. And the Lightning Link, in turn, was designed for Colt semi lowers.

There are so many variables in play when you go full-auto -- I like to compare it to a hacksaw (semi) versus a Sawzall (full-auto). The potential dimensional stacked differences that don't mean anything in semi become critical in FA.

When folks are having issues with a factory FA Colt, I tell them to return it to mil spec configuration, and then change one variable at a time. When folks are having issues with a conversion RR, I tell them to put it in mil spec configuration with mil spec parts -- in almost all cases, factory Colt -- and then change one variable at a time.

While quality control varies from one non-Colt maker to another non-Colt maker, Colt is indeed the primary Colt military contractor. And since so many of the components are subcontracted, a semi Colt is more in-spec, IMHO, than many non-Colt makers, who will often tweak the spex (like gas-port sizes, etc.) to make them run more reliably in semi, at the cost of less reliability in full-auto.

Yes, if you get a Colt semi host, you'll have to send the receiver off to M60joe to have it brought back to SP1 spex. But you can rest assured that every other part will be in-spec, unless Colt intentionally changed a dimension (and they always publicized the fact that they did so, so you can fix that. too).

Or you could just buy an SP1 host rifle -- which is what the LL was initially designed to fit -- and go from there.

YMMV.