I don't know dullh. I see guys all the time having trouble inserting a full double stack magazine into guns. Because the rounds are packed in so tight, the mag can be quite difficult to insert and get it to latch.
Part of the problem it too much force.
Often, when trying to insert a full mag, it is done too easy. Thus the mag doesn't seat properly. This is evidenced by the mag falling out when the slide is racked. To rectify this, most users go completely the other way and try to slam the mag in. This also causes the mag to not seat properly because the mag does a little bounce due to so much force being used. Obviously this leads to frustration.
I only say that because I've seen it several times. It mostly has to do with technique. It's like trying to slam the door on the old VW Bug. The car was air tight and the harder you tried the less likely it was to latch. The door had to be closed firmly, but smooth not trying to go too fast.
The right way to insert a mag is in one smooth motion.
First you index the mag in your support hand:
Holding it this way will help guide it in. I can insert a mag with my eyes closed because my index finger is in this position.
Then you put the flat back of the magazine against the flat back of the mag well:
Use just a tiny angle and it will be easier to mate up.
Then, using the heel of your support hand, thrust the magazine home with one, smooth, firm motion:
Again, I only say this because I've seen it a bunch.
I have a friend, a cop, who was having trouble with his SIG. For the life of him, he couldn't get a full magazine to seat. I watched him struggle with it a few times, then I took the gun and mag and inserted it the first time. I used the technique I've described above. Then I had him do it. Sure enough, it went right in.