If you don’t have a little special window on your AR magazine it’s hard to know if you loaded it correctly or not. I always put 28 rounds in my magazines, not the full 30. A completely full magazine can create all sorts of issues for you.
If you are trying to reload with your bolt forward, it makes it hard to get the magazine in all the way. I’ve also found that, for some reason, that top round doesn’t want to stay in the magazine correctly. So you try to load with the bolt locked open. Now, when you insert the magazine, the top round likes to pop out and sit inside the action just to create problems. Then, when you release the bolt, it tries to chamber the loose round and one from the magazine.
The last problem I’ve seen is that there is too much spring tension on the rounds in the magazine when it is fully loaded. Now the bolt doesn’t want to strip the top round and load it into the magazine because the magazine spring might be stronger than your buffer spring. This creates all sorts of issues that you don’t want.
So I load all my magazines with only 28 rounds to avoid all those problems. I’m going to share a couple tips about getting your mags loaded with 28 rounds. First take 28 out of the boxes and put them in one spot. If you are like me, you get 20 round boxes. So I empty one box into the pile and then eight from the next box. Now I have a pile of 28 (and that is it). I will fill my mag out of that pile and nowhere else. I also count them as they go in.
The real problem is if you have mags without witness holes or windows to know if the thing is loaded right after a while. For some reason, like no other magazines in the world, AR mags like to lose rounds. I’ve found lose rounds out of my AR mags everywhere. They fall out in my mag pouches (nylon or kydex), in my shooting bag, and even on the top shelf of my wall locker in Iraq where I had extra filled magazines stacked.
Now, which magazine is full and which one is missing a round (or two or three)? Here’s the trick. In a standard GI magazine, push down on all the rounds so they go into the magazine as far as they will go. If you can’t push down until it they stop, the mag isn’t full. Hold the rounds down as far as they will go and look at the back of the mag. The top of the top round should be even with the top of back strap on the magazine. I’m talking about that cut out part of the magazine where the round is exposed so that the bolt can strip a round out of the magazine and into the chamber.
PIC of back of magazine filled
Whatever magazine type you use, learn where the last round lines up when you push down as far as they will go.