Hi everyone...first post here!

I'm in the process of converting a std Colt AR-15 (pre-ban, no F/A...I've had it for about 25 yrs) into an M4-class, but the receiver extension tube (where the recoil spring goes into) is a @#$%& to remove. Can't get it off.
The rifle is in great shape. Only had about 2000 rds put thru it. Just want a change of scenery. Anyone else ever have this problem?

Greetings and welcome.
A dilema you have on your hands.  You need to put that lower in vise some how.  Mag block preferrably, so some good ole elbo grease can be applied.  Good luck.