If I cant get into a Colt course, I like the SIG course on the gas impingement AR. I think their M16 course is LEO only, but it doesnt hurt to ask since they sell their proprietary M4 piston uppers to the general public.
Nothing against the other courses mentioned in this post, but as an Armorer for a WPPS program, we are limited to who we can get certified by, and which courses get reimbursed for. In the same ball park about who will accept you since when not overseas, you dont carry creds that allow you into a LEO only course unless you are known to the course provider.
Did talk to a gent at FNMI about having FNH USA sponsor a Civie Armorer class, but they said it was good idea, but they contracted out some of their training to a third party out of Frederickburg, VA (maybe Crucible) and they tried to keep it LEO or MIL only - but that could change with pressure from consumers of their FN15 line.
Just food for thought.