AKs I load to the top, but not ARs. I've never had a problem with FALs loaded to capacity either, but if I ever had to trust my like to one, I would probably down load to 18.
I actually saw with my own eyes a mag that would not lock up because it was loaded to 30 while in Iraq.
We have been taught and are teaching that the whole "don't load your AR mags to capacity" is a myth. We recommend to not short yourself those rounds. I graduated USMC boot in 2000 and I've always been told in my non extravagant military career to download to 28 (or whatever) rounds because it will "wear the spring out". Well, as I got older and a little more outside experience, I have discovered that what was once taught to conventional forces was not always the best practice.
For provenance, I'm currently an LEA and a tac carbine instructor. We were taught through a "train the trainer" course from our tac team. The individual who taught our tac team and our agency is a retired SFOD-D (Delta Force/CAG) operator. I don't like parroting, but in this case, I think that gentleman's experience holds a ton of weight. As always, trust but verify for yourself.
Another myth dispelled is that it is in fact OK to rest your mag on the ground when shooting from the prone.
As such, I do not download any of my duty mags intentionally. They get downloaded when used during shooting sessions. Otherwise, they are fully loaded. I treat all magazines this way, be it pistol or carbine. One thing to watch out for if you decide to download is chambering the same round over and over again. This can cause bullet setback, or wear the primer out, or both, which can lead to much greater issues.
The one caveat with this is that you are using quality equipment and you have a schedule of maintenance on it.
With standard GI AR mags I download two rounds. Even if it doesn't affect reliability, trying to load a full GI mag is near impossible at times, especially on a closed bolt. With that said, I no longer own any GI AR mags. Every AR mag I own is a Pmag. With Pmags I load up to full capacity. Why short yourself the rounds. Every other firearm platform I own is loaded to full capacity also.
CGSteve mentioned something that many people seem to not notice or forget about. Rotating bullets in a mag used for carry or duty use is very important. Continually chambering the same round will cause bullet setback. This will cause malfunctions and excessive pressure situations.
I load all my magazines to full capacity except for my Black Dog Machine WASR 22 magazines.
All my AK 47, 10/22 BX-25, and XD magazines load fully without any issues, whether loading or inserting magazine.
I download my BDM WASR 22 mags to 25 instead of 30. I do this for three reasons.
1) Store my .22lr rounds in 50rd boxes, can load two magazines quickly this way
2) New magazines, spring is very tight and hard to load to 30
3) Loading less than 30rd allows for follower to act as a bolt hold open
I have owned aluminum "GI" mags that WOULD NOT seat on a closed bolt when loaded with 30 rounds. Not a myth. I discovered the latest one about 7 years ago when I attended a patrol carbine instructor class. Pretty embarrassing to have your mag exit the weapon while engaging targets. Even more embarrassing when you're so focused on the targets that you don't notice the aforementioned absence of magazine.
If the target were firing back, it could be fatal.
You don't have to download if you use only known good mags that you have physically confirmed will lock in with 30rds.
Pmags, on the other hand, have a slightly longer mag body, which alleviates the problem.
So, can I safely assume that this goes for all y'alls mags except for any collector mags you may have laying around?
You see, I have been thinking of doing this, loading most of my mags, storing them in ammo cans so as to maintain moisture away from both ammo and mag and have them on the ready.
The only thing is, I figure I barely get to the range, so, do I do more damage to ammo leaving them out of box or should there a reason for concern in this matter?
Also, do you leave mags loaded with plinking/target ammo or some good M67 type ammo?