I'd go as far as to suggest "mil-spec" is just another way of saying
"built by the lowest bidder"
Have you ever looked at a MIL-spec? The whole thing is clearly only possible for volume buyers. Unless you think that Colt is destructively testing one gun per batch for their civilian customers, just out of the goodness of their heart?
There is no such thing as a MIL-spec AR-15 on the commercial market.

maybe I was asking the wrong question.
I have a 20" HBAR but would like to know if I can buy a carbine length upper - 16" etc. I have heard that it may not fit due to some of the pins.
is it possible for me to buy a LMT, STAG upper to put on the lower receiver I have?
Exactly. Think of Mil-spec as really anal testing (destructive, non destructive) that colt does with the rifles throughout the production cycle. By definition, only the military rifles are Mil-spec as far as I know. That doesn't mean that other rifles or production runs at Colt are not up to excellent standards as well, it just means that during production they are ripped off the line to test for consistency/quality etc. several times at several stages of production.
Some Colt commercial (large hole front pin with a screw) require offset adapters to fit on non Colt commercial receivers. If your rifle has a screw for a front pivot pin you need an adapter.
If it has a normal 'push" pin you are good to go.
Not the most technical description but It should get my point across, as some Colts can switch others need the adapter.
also, (as I am selling this firearm currently). every other person messaging me about it asks "is it mil-spec"...
thanks for the info.




























