I shot my new M4gery today and had a few probs with my mags.  Got them here on the EE, they are NIW Labelle's.  When loaded to 30rd capacity the first 2-3 rounds were difficult to chamber or the first round would fire and the bolt wouldn't push the second round in the chamber.  Comments?

Check the following.

1. Use known good factory ammunition.
2. Check gas rings.
3. Check carrier key tight.
4. Check for binding of carrier in upper.
5. Check recoil spring length and strength.
6. Check for proper lubrication.
7. Try a different magazine.
8. Check for magazine follower binding.

The most common problems off the top of my head.

Quoted: Check the following. 1. Use known good factory ammunition. 2. Check gas rings. 3. Check carrier key tight. 4. Check for binding of carrier in upper. 5. Check recoil spring length and strength. 6. Check for proper lubrication. 7. Try a different magazine. 8. Check for magazine follower binding. The most common problems off the top of my head.

Wow, that's a list.
1 yes
2 they're new, don't know much about them but my brother said they're ok
3 I have no idea what that is
4 cycles ok
5 seems ok, it's new
6 looks good
7 Did it with both mags
8 I need to check that one.  ruler test ok?

This is a new gun, Stag lower Bushy upper, and the first time I've shot it so everything is new including the mags as theywere new in wrap pre bans.  Ammos is Winchester Q3131A from the Bass Pro sale.

I need to add when we downloaded the mags by 2 or 3 function was fine.  I didn't shoot that much or have much time so I didn't test thoroughly while I was there.

The mag when fully loaded is probally holding the rounds too tight in the mag.This can be caused by heavy spring tension or the follower could be binding when fully loaded.

Two things to look at would be:
Changing the follower for a newer one that doesn't bind when the mag is fully loaded.
If it already has a the new mil spec follower, try loading the mag full and letting it sit for a week or two which would help reduce some of the spring tension.  

Hope this helps you

Basically you could have two problems. Both magazines, or the gun is not getting enough gas or recoil energy to overcome the spring tension of a fully loaded magazine.

Since the magazines are new and USGI I doubt both of them are the problem. But they are the easiest to test by trying other magazines.

The other possible problem is harder to diagnose and involves many parts of your rifle. Make sure there is nothing keeping the gun from getting all the expended gas from the system and nothing binding your carrier.

Make sure the rings are staggered, make sure the carrier key (on top of carrier, gas tube slides into it when bolt in battery) is tight. Two hex screws hold it on, if it is loose, gas will leak and rob your carrier of recoil energy. Basically it doesn't go back all the way, therefore doesn't have enough energy to strip next round. Also if it is loose it can bind in the upper.

Make sure your front sight tower or gas block is tight and aligned with the gas hole, it may allowing gas to escape without going down the gas tube.

Make sure the buffer tube is on tight, if it is loose the carrier can get caught up in it during recoil and again bind.

Make sure the follower slides inside the magazine freely, take out the spring and tilt magazine back and forth.

That is all I can think of, I am sure others will chime in with suggestions.