I've noticed that Air Force builds are pretty much 'anything goes' which makes them fun in terms
of parts and especially barrels.

However, the thought came to mind, what does the AF do about adding a M4 feedramps barrel
to a A1 upper, non-feed ramp?

Supposedly it's really bad to do this, that said I ran a M4 upper with a rifle barrel for years and no issues.

Thanks.

Running a barrel with M4 feed ramps in a rifle upper is an "OK" configuration. M4 receiver and rifle extension is a no go. I'm surprised you didnt have feed issues.

They work, but  i wouldnt want one on battle field!

Air force was the dumping ground for basically obsolete pieces once the milspec changed for the ground pounders.  The spare parts basically ended up in AF parts bins for repair in many instances.  Also National Guard and used for training for CB's etc.  Check production years for 604 weapons and you will see gaps generally coincide with milspec changes and production using said pieces.  They didn't simply throw away much of anything like we do today.

Even H-D today will try and unload the earlier not so up to par repair pieces on the unknowing while they are fully aware of problematic pieces and their revised offerings.  Same with PC components capacitors and such. Some would call it good business and some wouldn't.  Depends on which side of the fence one is on.  The one selling the junk or the one buying the junk.

Not like a M-16 won't function fine or even better in many instances with the earlier production pieces.  Just wasn't up to the milspec as it changed.  AF didn't much care about milspec changes way back when. Tax coins at work and not waste.

oh right, rifle upper + M4 bbl = ok.
forgot, brain fade due to summer head cold.
thanks lads!