20 rd Magazine fails to hold bolt open

[mlberry]

I have a new M4 carbine with a 16 in barrel. I went to zero it and used an original M16 20 military magazine with the aluminum followers. The magazine works just fine in all respects in my Colt SP1. I used the magazine in my new rifle for the simple reason that it won't bottom out on my rifle rest. The 30 rounds mags are too long.

I noticed that the 20 magazine consistently failed to hold the bolt open on the last shot. Once I zeroed I then switched to the new 30 round magazines and the bolt stop worked perfectly. The 30 round magazine was a standard aluminum military magazine made by D & H as sold by Palmetto State Armory and the rifle is a PA15 also made by them.

Is there something in the design of the old 20 rd magazines that is different from the new 30 rd magazines that renders them less likely to hold the bolt open? Has anyone else had this problem?

[TaterTot]

Probably a weak magazine spring. How old is it?

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[quackhead]

Old style mags should hold bolt open as well. Try replacing the mag spromg as stated above

[mlberry]

Probably a weak magazine spring. How old is it?

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They probably date back to Vietnam. Still like I said they work fine in my Colt SP1. I wonder if the cyclic rate is faster in the M4?

[TaterTot]

They probably date back to Vietnam. Still like I said they work fine in my Colt SP1. I wonder if the cyclic rate is faster in the M4?
Faster and more abrupt do to the differences in gas system length and buffer system characteristics.

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[bamashooter]

If you insert an empty magazine and retract the bolt, does it then stay open?

[Stickman]

the rifle is a PA15 also made by them.

Has anyone else had this problem?


With almost any other brand of weapon, I would say to swap the magazine spring out and that would fix your problem. However, in this case, I wouldn't jump to that conclusion and would instead look at the lower and parts installed. You bought the cheapest thing possible from a company that is known to have used reject parts, and has numerous documented instances of parts issues and lack of QC. Hopefully you find this to be the least of your problems, but at least you have a known good weapon to fall back on in the event you actually need to rely on it.

[556BlackRifle]

If it holds open with a new 30 round mag and doesn't with a 40+ year old magazine, it has to be the mag. As recommended above try a new spring. This kit from Brownells LINK (http://www.brownells.com/magazines/rifle-magazines/magazine-parts/magazine-kits/ar-15-m16-usgi-20rd-cs-magazine-rebuild-kit-prod25018.aspx) will set you back $4 + shipping.

[mlberry]

Anybody else feel that way about Palmetto State Armory? Actually I'll just use the 20 rounders in the Colt and the 30's in the PA 15. I am actually quite impressed with it.

[TaterTot]

Anybody else feel that way about Palmetto State Armory? Actually I'll just use the 20 rounders in the Colt and the 30's in the PA 15. I am actually quite impressed with it.
Their qc is known to be spotty. Their focus is on sales volume not quality of product

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[Singlestack Wonder]

Faster and more abrupt do to the differences in gas system length and buffer system characteristics.

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This.....replace the old mag springs....

[556BlackRifle]

Anybody else feel that way about Palmetto State Armory? Actually I'll just use the 20 rounders in the Colt and the 30's in the PA 15. I am actually quite impressed with it.

So, you are now saying that the 20 rounders lock the bolt back in your Colt but not in your PA15? If that's the case, read Stickman's post above. And that's nothing to be impressed about.

[mlberry]

I said that the 20 rd mags worked fine in my Colt. And the 30 rd mags work fine in my PA15. But I think that with the vitriol this thread has inadvertently inspired I will leave both this thread and this forum.

[KalashniKEV]

Is there something in the design of the old 20 rd magazines that is different from the new 30 rd magazines that renders them less likely to hold the bolt open?

Quoting PEO - Individual Weapons:

"Tan is the plan, if it's Green start to lean, if it's Black send it back, if it's Aluminum WTF?"


Anybody else feel that way about Palmetto State Armory?

PSA = Junk Factory.

https://www.m4carbine.net/showthread.php?190153-PSA-BCG-s

[TaterTot]

I said that the 20 rd mags worked fine in my Colt. And the 30 rd mags work fine in my PA15. But I think that with the vitriol this thread has inadvertently inspired I will leave both this thread and this forum.
? PSA has known QC issues, it's well documented. Your PA15 may be fine, just check it over. A carbine gas and buffer system operates much faster than a rifle system so those 40yo springs might not be able to keep up. Springs and mags are wear items and need to be replaced periodically. In fact the original mags for the M16 were intended to be single use.

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[Hamms]

Does the PSA lock back on the 20rnd when cycled manually? That's the quick check to point towards weak mag springs, or out of spec lower.

[tehpwnag3]

I also have one of the Nam-era M16 twenty rounders and, IIRC, both the spring and follower would have to be replaced, but even then there might be fitment issues with doing that. It's the way the spring attaches to the follower that makes it different from modern 20's (even other metal ones). IMO, it's a neat conversation piece but you would be best served picking up one or 10 of Magpul's G3 20's on-sale now at Brownells!

http://www.brownells.com/magazines/rifle-magazines/magazines/ar-15-m16-pmag-20-round-gen-m3-magazines-prod75488.aspx?avs%7cManufacturer_1=MAGPUL

[mlberry]

Like I said the older mags work just fine in the SP1. After all that rifle was designed with those 20rd in mind. I think the springs were designed with a lower rate of fire in mind. I did get a new MAGPUL 10 rd mag and the spring is decidedly stiffer than the old 20s.

[Hamms]

Don't care if it works in the SP1, check it in the suspect rifle by cycling it manually. If it locks back manually, its probably a weak mag spring, regardless if it works fine in other rifles.