I have a Colt 6601 that has a very tight mag well I think.  I have two (2) Okay 30 rnd GI mags, six (6) Thermolds and one (1) Colt 20rnd.  They all fit tight and do not drop free with the exception of the 20 rnd mag.  The Okay 30's will disengage from the mag catch when the mag release is pushed but will not drop free and the Thermolds will not disengage from the catch and the left hand has to be used to remove them.  I can tell where the friction is occuring because the back of the thermolds have finish on them from the mag well to the left and right of the spine of the mag.  I've heard this is common with 30 round mags but my Bushmaster will drop them all free without hesitation.  What gives?  Does the Bushy have a bigger well or is there something wrong with my Colt lower?  Can the factory open up the mag well to get these mags to drop free?  Is it even that big of deal?  Any help would be appreciated.

Re the Thermolds. my experience is that they are a bit thicker, front to rear, than the metal mags.  I've had to take a bit of material off the rear rib, on the top inch and a half, to get them to drop from my Rock River and Bushie lowers.  On the other hand, if your Colt is tight on GI metal mags, it does sound lioke an exceptionally tight mag well; fairly unusual on Colts.

Was it mine, I'd give Colt service a call, and see what they have to say[:D]

Mag change drills...

About 934 of them...

Square you right away!
[;D]

Its not a big deal, some are tighter than others. Me likes them tight, they will become loose after a lot of use.