Are they not capable of being stored long term fully loaded, or something else? 2 x 20-round Gen. M3, 1 x 30-round Gen. M3, 1 x 30-round Gen. M2, stored loaded for ~8 months (maybe longer, but I don't remember for certain). Every one completely failed to lock into the well, not even a hint of catching and falling right back out. I removed one round at a time, checking each time, and wound up taking 3 rounds out of the 30s and two out of the 20s. After this they locked in and proceeded to function 100% with the reduced loading. The mag catch has plenty of protrusion into the well and the spring feels stiff. I had not previously shot them; this was their first range outing. Rifle is a 2018 Ruger AR-556.

Did you store them with the cap in place, or without? Mine are all stored with the cap on.

Stored without the cap will spread the feed lips.
Shouldn't affect not locking in.

Do they lock in with the BCG locked back?
They may be bound up and have no room to move if trying to insert with the BCG closed.

I still had one Gen3 30 rd. that had been stored fully loaded. With the bolt closed, it would not lock in. I took five cartridges out before it would. It did lock in easily with the bolt open. Compared to a new mag, the gap between the feed lips does look slightly wider.

Because of stocking up during the Grandpa Badfinger regime, they are plentiful and cheap, and the gun ran perfectly with the single P-Mag that it came with, I have a number of Gen2 and 3 unopened, so I compared them. The Gen2 has no cap on it, but the Gen3 does. It does fit over loaded cartridges. I assumed this was a shipping protector. Nothing in or on the packaging says what it's for, and I don't see where it would apply compression or inward pressure on the feed lips. But if leaving these caps on fixes the problem, I'll take the win.

I further assume the feed lips won't spread if the magazine is left in the gun?

The covers work by pushing down the topmost round further into the magazine just enough so that there's no pressure being exerted on the feed lips. This photo is a collage of a 30-round TMag with the cover on and off. The graphics molded into the side of the mag can be used as a reference to see that downward shift of the rounds. The crescent shape above the feed lips in the right-hand side photo is the flashlight bezel.



I wouldn't be concerned with the feed lips spreading when locking a loaded PMag in the magazine well as long as it's under a closed bolt carrier group. The BCG will basically do the same thing as the cover in that the pressure on the feed lips will be relieved when the topmost round is compressed against the underside of the BCG.

Might be rifle (rifle type) dependent. Don't own an AR but I've had 5.56 Pmags loaded for years that lock into a SCAR and X95's without issue.

quote:

The covers work by pushing down the topmost round further into the magazine just enough so that there's no pressure being exerted on the feed lips.
[...]
I wouldn't be concerned with the feed lips spreading when locking a loaded PMag in the magazine well as long as it's under a closed bolt carrier group. The BCG will basically do the same thing as the cover in that the pressure on the feed lips will be relieved when the topmost round is compressed against the underside of the BCG.

If you wish to put the rifle in the readiness mode known as "cruiser ready" (full magazine, empty chamber, closed bolt and safety on), since the safety can't be put on without the action cocked, being able to lock in against the closed bolt is necessary.

i was about to mention that i had 4 20 rounders loaded for almost 2 years before using them with zero issues . i had the covers on mostly to keep dirt/dust out... but i didn't realize it also relieved pressure on the feed lips.

the more you know indeed, lol

Wow.. I learned something today..

I didn't know that the dust covers were designed to relieve pressure on the feed lips.

If I ever store any of my P-Mags loaded, I will definitely use them.

(Even though I have quite a few, I am still a metal magazine type of individual- Okay, Brownells, etc..)

Yeah, and that's why Magpul now selling the dust covers separately is such bullshit.

On my 20 and 30 round mags that I have all of them will lock in against a closed BCG when loaded to capacity, M2 and M3 mags.
On the few I just looked at there is about 3/16" or so compression left at full load.
About the same as the metal ones I have.

I use the cover to unload mags by using the latch as a poker.
I haven't bought any in a while but I don't think they come with a cover now but can be bought separately.

I hope I didn't throw all mine away. I hope they're in a bag somewhere. I only keep a few loaded.