I have a USGI 20 round magazine that will not work with 20 rounds in it.  When I close the bolt it hits the round and stops.  It will not strip it out of the magazine.  If I only load 19 rounds in it, it works fine.  Any ideas?

It must be an oldie. Youll just have to load it with 18 or 19 rounds. lol

Sounds like someone took it apart and put it back together wrong.  Check the coil on the follower - it should be 'just on' not with an entire loop of the spring.

Improper assembly will limit the magazine.

A properly assembled magazine will be able to hold 21 rounds.  However it will only feed with 20 rounds or less.

This of course assumes your USGI magazine has the proper alloy follower.  Some numb-nuts think its a good idea to replace it with a green follower [slap].  If the front leg of the GF isn't trimmed right it will also limit magazine capacity.  For best results keep the USGI 20's with their alloy followers.

Forest- I took it apart and it looks like the spring is on correctly if I understand you right.  It does still have the alloy follower.  Do you have any other ideas?  Thanks for your time.