I'm having troubble getting the mags to lock in my AR that I just aqquired. It's a Colt slabside upper with a new Colt carrier/bolt assy. The lower is an Eagle (Armalite).

When the bolt is forward you have to really smack the mag to get it to latch, if the bolt is locked to the rear the mag just slides right up and locks in. This happens with the 20rd. Colt mag and the 3 OK Industries 30rd magazines that came with the rifle.

I'm prior service (AF) and I know you're supposed to give the magazine a good hit on the bottom to make sure it's seated but this is way past that, besides it just started happening the other day after I shot the rifle for the third time. I looked at the mag catch, it sits flush and seems to have good spring tension. It dosent look worn either.

I figure there's something simple I'm missing or it's my simple mind. Any ideas?

Me too. I've just taken them out of the shtf pile.

Sounds like a typical problem encountered when loading magazines to maximum capacity... Try loading the 20's to 18 and the 30's to 28 to see if that eases the insertion any...

Yeppers.... load the 30's with 28 and mark your top round with a sharpie... That way you can seat the mag easier and when you charge the gun you can pop out the mag and see the marked round is gone so no need to press check the gun to insure it's live... Another option is to look at the top of the mag and see which side the top round is on... Just another option... I like using the sharpie so if I run accross a mag with say 24 rounds in it... no mark... less than 28... but I've been accussed of being simple....

So the mags are new?  New springs tend to be stronger before being used for a few times.  It's just part of breaking them and the rifle in.