I have a Colt 16" HBAR. I have recently discovered that fully loaded 30 round USGI mags are difficult to fully seat in the mag well.  It seems to me that an excessive amount of force is needed to engage the mag catch and fully seat the magazine.  This problem does not happen when the bolt is latched in the rear position or when the magazine is not fully loaded. Also, I have not experienced this problem with my fully loaded Colt 20 round magazines.

Any suggestions on how to solve this problem would be greatly appreciated.

When instering a magazine:

I always use a firm 'SLAP' on the base of the magazine to seat mine.  Full 30 rounders are sometimes difficult to seat.  

Rotate the gun 90 degrees clockwise (magwell is facing your left).

Insert the fresh magazine (using your left hand).  After inserting it, strike it (on the floorplate) with the base of your left hand.

Then firmly grasp the magazine (still using your left hand) and attempt to remove it by force.  This insures that your magazine is inserted and seated properly.  

If you cannot pull it out with your hand.

Rotate the gun 90 degrees counter clockwise and continue to assess/engage your target.  [;)]

TRG

Nothing unusual about this at all.  All the AR's I've ever personally shot were the same way with any full magazine.

It shouldn't be a problem, though, because when you're shooting, unless you're doing a tactical reload, you'll be replacing the mag on an open bolt rather than a closed one, so the mag will insert to the catch with very little effort.

CJ

What they said.  Plus, if you are carrying loaded mags for  a potential tactical (i.e. weapon still chambered to fire) reloads, simply carry mags downloaded a round or two.

Thank you all.  I am relieved to know my rifle is not out of spec.

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Not out of spec at all.

30 rounds in a magazine exerts some serious upwards pressure. Remember the first round actually sits above the bottom of the bolt when the bolt is back.

So if the bolt is forward, it takes a good slap or alot of pressure to fully seat the magazine.

Just slap the heck out of it and go. And take a quick glance at the magazine release to see if it has returned fully to its locked position.

matt33,

Is it difficult to insert EMPTY magazines? Do your mags drop free?

I always load just 29 rounds and don't have that problem.