I've got five 30 Rnd mags that worked fine for almost a year now .  I go to the range two days ago and 3 of the 5 are all f*%ked up.  The last round just pops up into the receiver and the bolt locks back. Occasionaly half the way through a full mag, TWO rounds will release from the mag and BECOME WEDGED IN BETWEEN THE LUGS AND THE BOLT!!!  The top of the mags seem rather flimsy now, and don't hold the first round when pushed in.  The mags are marked on the floor plate as follows:
(colt pony) 5.56mm
Colt's Firearms Division
Colt Industries
Hartford, Conn. U.S.A.
Any help is greatly appreciated, and TIA
VT4Me

Sounds like the feed lips are starting to give. Have you looked at the rear of the feed lips for cracking?

I had a simlar problem recently that was caused by the mag catch. It was a too small for the receiver so the mag would sometimes get a bit loose (read that: sit too low) causing misfeeds. But that doesn't sound like your problem.

Do you normally keep the mags loaded.  While the general concensus is that a constantly loaded mag won't wear out the spring, it can cause the feedlips to flex outward, causing the problems you described.  It could just be that your mags are at the end of their lifespan.  Do the feedlips look worn to the point that they are relatively sharp edges?  If that is the case, then the mags trash.  If the problems are just due to spread feedlips, you could try gently squeezing them back together some with a clap or vise grips and see if that cures your problems.

Thanks for the input you guys.  I tried squeezing the feedlips together just a bit between some soft wood and a vise.  I think these mags are just shit though.  Again, thank you.  VT4me

My .02..

A shitload of civilian owned mags are USGI surplus.

A shitload of guys *think the floorplate makes the mag. Active Duty strips them down in piles for cleaning and puts them back together. No telling what goes with what.

Keep those dancing pony floorplates. They make you a little change someday.

It sounds like they hit the expiration date.