Get your mind out of the gutter.....I'm talking about AR's.

I have a Colt Match Competition HBAR II post-ban.  I recently bought a Bushmaster lower also post-ban that I'm going to use to build another rifle.  I was under the impression that Colt changed the pin sizes on their post-bans, but my Colt upper fit just fine on the Bushmaster lower, which is mil-spec?
Just a little confused.  Any help would be appreciated.

older colts have a large pin on the front.
you have a new colt so you can change with yur other uppers and lowers.