What, if anything, happens to an AR-15 magazine if you leave it loaded for years? I’ve seen a ton of debate on the internet, so back in 2014 I decided to run a test. I loaded two Magpul PMag’s, setting one aside to test in five years, the other set aside to test in 10.
Five years is up, so how did the magazine do? Let’s find out.
Magpul M2 PMag
The magazines I am using are Magpul PMag M2 with a dust cap over the mouth of the magazine.
This dust cap also slightly depresses the rounds in the magazine which takes pressure off of the polymer feed lips, in addition to keep crud out of them.
There are 5 basic parts of a Magpul polymer magazine. They include the outside shell, the follower (the part the bullets sit on), the spring, the spring base and the magazine base.
When it comes to storing ammo in magazines long-term, the two biggest concerns in the prepping community seem to be whether keeping a spring under load that long will weaken it, and whether leaving that much pressure on the feed lips will cause them to deform.
As mentioned above, the cap depressurizes the feed lips, but it does so by increasing the compression of the spring even more than if the cap were not in place.
The Full 30
Although I normally only load 28 rounds into a 30-round magazine, for this test I wanted to give it as big of a challenge as I could. I loaded it with 30 rounds of steel-case ammo
Let’s look at how the five parts held up
Two of these parts can just be ignored, as the follower and the spring base basically are just plastic pieces sitting there doing nothing.
The magazine bottom also can at least mostly be ignored, but since it is under pressure and it could have bulged, becoming difficult to remove, I’ll mention that it didn’t.
The body got a bit scraped up over the five years of sitting in a drawer. It went into that drawer at my house on September 10, 2014 along with it’s 10-year buddy, so it’s picked up a few marks. The feed lips look perfect, however.
The spring looks good, and most importantly it measures the same length as other second and third generation Magpul springs. Once I figure out a way to measure the pressure of the spring, I’m going to include that in an update to this article.
The spring on the left is the 5-year Gen 2, while the spring on the right is a newer Gen 3.
Again, the test magazine Gen 2 is on the left and a Gen 3 with window is on the right. The orange painted section is so you can see the “rounds left” indicator.
The Test: How did it shoot?
We shot the magazine dry at the range today, following a full range session in a Del-Ton M4 wearing Magpul furniture (more information about this gun is available by clicking HERE!).
The rifle was hot (as in far too hot to touch) and it’s far from a premium AR, so I thought it would be a good test.
The magazine seated nicely into the mag well, took the first round into battery, then Spice proceeded to drill one two inch hole in a piece of paper downrange (one 1/2 inch off flyer). The magazine (and gun in general) operated flawlessly shooting steel cased rounds after a day’s worth of shooting rot-gut Tula steel.
Bottom line
As far as I can tell, there were no adverse effects from loading up this magazine and leaving it stored full. It will be interesting to see how the 10-year magazine does as well as a 5-year AK-47 magazine that will ‘”come ripe” next month.
Thanks for going the extra mile on this.
I did a similar test involving a Sig P-228 magazine, manufactured around 1990 in Germany. I left it loaded for five years and it performed flawlessly. In fact, I still use it to this day without issues.
Metallurgy has improved over the years, so magazine springs have benefited from improved steel. I think the most likely problem is the feed lips on a magazine, particularly older ones that haven’t benefited from better metal.
When I was first in Vietnam, I went to a range to get my battle sight zero. I fired one shot and nothing happened after. I went through the stoppage drill, and still nothing. I was fairly inexperienced with firearms then, and I was stumped. The Gunny running the range knew what the problem was immediately. Bent feed lips. He showed me what to look for on my other mags, threw the bad one out in front of the firing line and told me to shoot the crap out of it so it couldn’t be accidentally used again. I happily did so. It was a 20-round mag as the Marines hadn’t gotten the 30-rounders yet.
“Once I figure out a way to measure the pressure of the spring,”
There is no such thing as spring pressure. It is spring rate, also sometimes called stiffness or erroneously called weight. For simple springs, it’s commonly expressed in units of force per distance. For instance, a “10 lb. per inch” spring would take 10 lbs. of force to compress 1 inch. An additional 10 lbs. would be required to compress it an additional inch, and so forth. See Hooke’s Law.
Thank you for that test. Magpul says they’re good loaded for 6 plus years. Good Job.
As an Engineer, when your are designing a spring, you are more concerned with the number of cycles a spring will endure during its life than the load. That is assuming the load is not so great as to cause the stress on the spring to exceed the yield point of the material it is made of. Within the bounds of practicality whether the spring is loaded or not makes no difference to the spring if it was properly designed.
How about that GUN REST?
Ok, so the folks at our local range are kind enough to leave some of their ‘re-manufactured’ equipment out for anyone to use. That includes a set of old car jacks with rubberized rests on top. They work well enough, and they’re There. I call that a win. (They also have up a big ole mail box where people stash extra targets, staple guns, and ear protectors. Very handy if you’ve forgotten something.)
I have a Del-Ton M4 and it functions as reliably as my Colt A2 and delivers the same (perhaps even slightly better) accuracy.