Why don't you test a couple out and then let us know.
You will never get people to agree as to whether or not leaving leaving magazines fully loaded will weaken the springs and cause jams. On one side there is the group that says the springs are so well made today that it's not an issue as it may have been years ago. Then there are those that say repeated cycles cause spring weakening not leaving the mags loaded. These are good points and probably accurate to some degree.
I'd like to bring up a couple of issues. One is that we are in a gun bubble and the current manufacturers are cranking out every gun and accessary they possibly can. There have been stories of quality issues as the manufacturers increase production and worry more about quantity instead of quality. The same thing happened during the time period leading up to the Clinton Gun Ban. My question is do you know who is really making all of the magazine springs in your favourite mags? You may have gotten great _____ mags in the past from _______ but as production increases is the quality still there and will they hold up just as well in the long term? Are the manufacturers of ____ magazines contracting out some of their work to inferior sources? There are companies today that still have a poor reputation because of the corners they cut in an attempt to increase production before the Assault Weapon Ban went into place in the 1990's.
I was taught in the Marines to load the magazines under full capacity to keep the springs from weakening. I don't know whether this was necessary or just old doctrine being taught. I do know that the Marine Corps has almost 100 years of history using magazine fed weapons so they should know what they are talking about. I had a few law enforcement friends that I've lost touch with over the years. I do remember that they were told to rotate their full mags and not to use the same topped off mags every week. While not all law enforcement agencies are professional these guys (from 2 different agencies) did use guns daily and they do get the updates from other agencies when weapons failed when needed. They were taught to carry fully loaded mags and swap them out with other previously unloaded mags each week.
A friend of mine recently lost her father. He was never a gun guy but he did keep a few inexpensive firearms around "Just in case." These guns were shot once or twice and then put away for years. As my friend is also not a gun person I took her to the range and showed her how to shoot the .25 cal Beretta she inherited. The gun was rarely shot and left with the one mag it came with fully loaded for years. Guess what? It jammed on the last one or two rounds every single time it was shot. The magazine was left fully loaded for years. She and her husband did not even know how to unloaded the gun for safety reasons so I saw the gun exactly as it was when she picked it up from her father's house.
This gun was probably over 20 years old so the magazine technology has probably evolved quite a bit. The point is you just don't know how old your mags are (if you bought used), who really made them or if the quality was ever there in the first place.
I have a Kimber (9mm) (with Kimber mags) that I've been shooting a lot for the last several years. It stays loaded with 2 rounds less than full capacity. I've had no problems. The magazines have also been compressed countless times over the years as this is my favourite handgun. Still no problems.
I keep my mags loaded a few rnds under full capacity for peace of mind because in the end it's not going to matter if my 19 rnd XDM mags have 16 rnds in them or if my 9 rnd Kimber mags have 7 in them if they are needed for self defense. I've got extra mags loaded and spend a lot of time shooting and hope that accuracy and muscle memory will make up for having 2 or 3 rnds under capacity if I ever need these weapons for defense. I do know that they won't jam due to weak springs if the "Top off your mags" group is wrong about compression cycles weakening mags springs.
I respect the opinions of those that believe compression cycles ruin magazines instead of leaving them constantly loaded. We've all seen plenty of posts from those that say they leave their mags fully loaded with no problems. This is indisputable. I do have to wonder if the quality of the factory Glock mag, Magpul magazine, XD mags, etc. spoils some of us gun owners. You can probably do whatever you want with these mags and be ok in the long run. Can the same be same for the guy that owns the Llama, Phoenix Arms or Raven? What is the quality like for the mags supplied with these less expensive pistols that some people buy?
