AR Magazine Doesn't Hold Bolt Open After Last Rounf

[alamogunr]

As the title says, the bolt is not held open after the last round is fired from this magazine. The mag is labeled "Master Molder" with Wilson N.C. in a circle. It also says "Law& Gov't Use Only" on the other side.

Obviously, I'm not particularly AR savvy. I was trying out 2 AR's that I had assembled when I discovered this. Actually, the only things I assembled were the lowers. I purchased the uppers either fully assembled or a barreled upper and BCG.

Other magazines that I tried kept the bolt open after the last round was fired. It is really not a problem for shooting at the range, I'm just curious if this is a defect or is there a reason for this mag not working the same as others.

[Bzcraig]

If using the exact same ammo in other mags works then I would definetly suspect the mag.

[MUSTANG]

Is it a surplus Military Magazine? Often surplus Mil Mags were surveyed out of units because of problems reported to armorers; they are then sent to DRMO (Defense Reutilization and Management Office) where they tend to be tossed into pallet sized boxes and sold in bulk at auction. They are then often bought by small entrepreneurs who may or may not rebuild them back to operating condition before sale to the public. "Surplus" magazines may or may not be a good buy.

If your specific magazine fails to lock the bolt open after multiple uses (I recommend trying it loaded with 3 rounds for testing each time); I would recommend painting a portion with yellow, blaze orange, or other color so that you know it's not locking the bolt to the rear each time. This way if you ever need the AR for SOCIAL occasions; you can ensure you are using a good magazine; or from visual indications know that the bold IS NOT going to lock open after the last shot.

One can repair many malfunctioning magazines; but it is a skill that eludes most of us (and armorers/gunsmiths too); which is why most military and law enforcement will simply survey out of service a magazine that is problematic.

[daengmei]

Don't recall the brand, but I have an AR10 mag that is fairly new and it does that. The magazine follower is plastic and the bolt has "peened" the follower somewhat and the bolt no longer stays back after firing the last round. It will lock back if I work it nice and slow but the slightest touch to the rifle sets it free.

[Boolit_Head]

Either the previously mentioned mag issue or not enough gas to lock back the bolt. Since you assembled them yourself did you make sure the gas block is lined up? You have not described your set up but most blocks are designed to have the front cap for the split hand guards. If you are using a free floated guard then the block should not be set against the barrel shoulder. There should be a .25 to .30 gap between the shoulder and the block. The way to tell if you have a set screw type is to remove the rear screw and flip it over so the screw hole lines up with the gas hole. You can then insert a feeler gauge to measure the gap. Flip it over with the right gap and a reasonable effort to center it and most gas problems disappear. Even if they are purchased there is no guarantee that they are lined up correctly.

[buckshotshoey]

Inspect the follower. It is probably defective. Take floorplate off of the mag, pull out spring and follower, and swap out with another of your mags with same capacity. That will tell the story. Make sure the follower is facing the correct direction. Most probs associated with bolts not staying open is due to this.

[alamogunr]

I did a Google on "Master Molder Wilson NC". Most info returned said they were mostly junk. One poster was favorably impressed but not sure it was apples to apples.

I've only got two so they will be relegated to range work only. Since I will probably give these guns to my sons or grandsons, these mags won't go with them. Too many others to worry about it.

Thanks for the responses.

[Green Frog]

If for some reason you regard this magazine as worth saving, buy some MagPul™ replacement followers (the ones I got were yellow) and expect your problem to disappear. If it were me, however, I'd discard the offending magazine as undependable and likely to mess up in some other way. Just my 2¢.

Froggie

[S.B.]

Plastic or aluminum? I've heard even Magpuls won't work in all ARs.
Steve

[alamogunr]

Plastic or aluminum? I've heard even Magpuls won't work in all ARs.
Steve

Not sure if you are referring to the mags in my OP, or the followers that Green Frog referred to. The mags(2) in question are molded plastic 20 rounders and the followers are plastic. I have a few 30 rounders and a couple of 40 rounders that are plastic that I have not tried. I should do that soon. All the rest are 20 round metal magazines.

[Lead Fred]

I have 30 of them. They have worked flawlessly so far.

But then what can you expect for $4 bucks

[S.B.]

I was replying to the OP. Several mentions of plastic not working in all ARs, ie: the newer Sigs etc.
Steve

[molar]

Bad follower.

As someone else mentioned, mark it for range use only.

Go out and buy some PMAG's, Lancer AWM's, D&H, NHMTG, or OKAY/Center mags

[JonB_in_Glencoe]

As the title says, the bolt is not held open after the last round is fired from this magazine. The mag is labeled "Master Molder" with Wilson N.C. in a circle. It also says "Law& Gov't Use Only" on the other side.

Obviously, I'm not particularly AR savvy. I was trying out 2 AR's that I had assembled when I discovered this. Actually, the only things I assembled were the lowers. I purchased the uppers either fully assembled or a barreled upper and BCG.

Other magazines that I tried kept the bolt open after the last round was fired. It is really not a problem for shooting at the range, I'm just curious if this is a defect or is there a reason for this mag not working the same as others.


I have 30 of them. They have worked flawlessly so far.

But then what can you expect for $4 bucks

alamogunr,
that's the thermold mag that's available from Numrich. I haven't had any issues with the ones I bought 3 years ago. I did just order some more, in the last month...I haven't been to the range with any of those yet. I hope they function like the ones I bought 3 years ago. For the price, they are kinda a "throw-away" mag. That's what I'd do (throw-away), if it didn't function properly or if the follower became worn and didn't hold the bolt open on last shot.
That's my 2¢
Jon
https://www.gunpartscorp.com/ad/1163640.htm#1163650B

[Shiloh]

Do other mags work well?? Can a buddy try it in his rifle to check??

Shiloh

[alamogunr]

I only tried one other mag, a steel Brownell's brand. It worked fine. I only know of one friend with an AR and he is in Florida right now. I will get him to try the plastic 20 rounders when he has time.

I guess my OP sounded as if I was testing magazines but really all I was doing was shooting these guns for the first time and testing overall operation. The guns worked fine unless there is something about them that is causing the mag problem.

[OS OK]

I've got a 14-45 that came with plastic followers and started doing that early on. I can see where the followers are worn in the spot where they push up on the slide lock metal part that locks the slide back...I replaced the mags with mags that have the metal follower and that fixed the problem.

Plastic in our weapons...who started that mess?