Various Uppers that fit which Lowers?

[Alchase]

Is there a "comprehensive list" of Uppers and which Lowers they will go with?

[jasnt]

I always thought any upper would mount on any lower as long as they are both ar15

[snowshoes22]

I believe some colt lowers had different size pin holes so they couldn't accept m16 parts. I think it is mostly an older colt thing

[Alchase]

I believe some colt lowers had different size pin holes so they couldn't accept m16 parts. I think it is mostly an older colt thing

I had heard that myself

I believe some colt lowers had different size pin holes so they couldn't accept m16 parts. I think it is mostly an older colt thing

Don't M4s have the same issue?

[jbauch357]

The large/small pin variants should only effect the parts you can put into the lower, most aftermarket parts manufacturers sell mil spec and large pin variants of fire control group parts so you can still get almost anything you want.  To be safe if you don't want to deal with it, just make sure you get a standard mil spec lower.

[724wd]

I've got a large pin colt HBar upper on a small pin DPMS lower.  Using an offset bushing.  It's a bit hinkey, but I was ringing the 400 yard gong at fernan with issue carry handle sights.