My mag catch is not holding in the mag. It just falls out. I have tried adjusting the catch in clockwise but it does not seem to make a diference. Any ideas?

Start off by removing the catch.  Press the mag catch button all the way in with a pencil, and then turn the catch (other side) counter clockwise to remove.

You should have a catch, spring, and button.  Now lightly lube the parts, and reinstall them.  When completed, the threads on the catch should be level with the button face.

Now shotgun the rifle open (lower/upper), and insert a mag into the lower until it locks in place.  Gently lower the upper and lock the upper in place (rear take-down pin). Press the mag release, and the mag should drop down.  Now push the mag back up, and then using the palm of your left hand, give the bottom of the mag a blow to seat it back in the rifle.

Also, on a fully loaded mag, with the carrier/bolt all the way forward and locked, you will need to love tap the mag to seat it in the catch.  The fully loaded mag asserts a lot of tension on the bottom of the carrier, and the tap will force the rounds back down into the mag to allow the mag to seat/lock.

ditto on what Dan523 says, but you also may want to check your mag(s).  The English ones need the top of the mag catch opening very lightly filed sometimes, not saying they are the only ones that fail to seat though...

I have tried just about everything already. Now, an empty mag goes in fine, it seems the top round hits the bolt and stops it from seating.

What mag was giving you problems in particular?  I ran into a similar issue with the first Brit mag I got but 'love taps' took care of it.

- BUCC_Guy

Have you tried downloading your mags by 2-3 rounds when loading on a closed bolt?  A full 30 rounder is very difficult or impossible to seat in some rifles, due to the fact the spring can not be compressed any more than it already is, and that you're pushing on a relatively heavy stack of ammo within the mag.

Yeah, the downloading thing worked. I have mostly USGI mags, so I think they are ok. I guess 28 or 29 rounds will have to be the norm [:(]