AR-10 308 mag issues

[DIYguy]

Been working on finalizing a new PSA PA10 308 build. There's typically a journey to get these things tuned just right for gas blocks, failure to feed, failure to eject etc. Then add a can tweak some more. I've been encountering a different failure to feed issue. I always run BAD levers on all my AR platforms and my normal process is to lock the bolt back before inserting my mag and then when I'm behind the glass flip the lever to drop the bolt. I've been having a lot of issues when I initially drop the bolt not striping a round at all to load. Empty chamber. Drop mag, check rounds, tap to make sure rounds seated to rear of mag, Charge bolt, reinsert mag, drop bolt and nothing. Tried a test as the top round was on the left side of mag, stripped that round so top round was on the right and it worked. This was the start of my mag questioning and inspection.
Because all my rounds so far have been for load development I'm running them past the Labradar and shooting off the bench. Target berm is slightly lower than range house which means I have to use ten round mags as twenty round are too tall for the bipod.
When I got back to my shop I started checking my P-Mags. The one I've been using looks like it has a small bite out of one of the flanges on left side. Not the only difference. Gun shipped with a twenty round P-Mag but as mentioned too tall. When I compared the ten round with the twenty round was shocked to find out not the same. Both are Gen3 but the followers are quite different. I'm attaching some photos to show the comparison.
The mag in the center of each photo is the twenty, two tens on each end, one is used, the others are new. Lets play a game and see how many difference we can find.

 

[fast99snake]

I had trouble with the pmags in an ar10 build very similar to yours. Swapped to steel duramags and issue was fixed.

I run pmags in ar15s all day no issue but something with how large the lip is around the top causes fail to feed issues. At least in my experience. Buy some steel mags and call it a day.

 

[LRRPF52]

There have been many changes with the 7.62 NATO PMAGs over the years. A lot of this was to accommodate the variations in rifle manufacturers with their bore datum relative to the mag catch location on the lower receiver, the different bolt catches, and just how different large frame guns perform.

Nobody but a few are on the same sheet of music, and there is no TDP with supporting armorer’s gauges to check BCGs, receivers, extensions, bolts, extractors, firing pins, upper receiver dims, gas tube locations, carrier rail lengths, etc.

The 1st Gen 7.62 PMAGs worked well in some guns, but didn’t in others, so Magpul made changes. The DPMS GII was notorious for not working with the Gen 1 mags because the bolt was smaller, with smaller bottom lug engagement. People modified followers to locate the last round cartridge in presentation in a more ideal orientation.

What really needs to happen is that a rifle manufacturer build the rifle around a specific magazine dimension set, and make that known.

One magazine that usually solves large frame feeding problems is Lancer.

I have zero expectations of any type of reliable performance from any of the race-to-the-bottom assemblers though. Let them address the problem.

 

[BAMAboy18]

I have 2 308s & a 6.5cm, I just built another 6.5 for my friend. On his, I discovered a Hexmag & a steel CPD?? mag wouldn't lock the bolt back, even tried an upgraded catch that didn't help, where a P-mag would, (20rnd) did fine. Went back and checked all 3 of mine, exact same results. I don't have any 10rnd P-mags, but was wanting a few. Definitely see the difference in the follower there, and obviously the potential for problems.
Someone was trying to tell me "AR-10/SR-25 we're not compatible with DPMS P-mags"??
All 4 I built have the SR-25 slant cut receivers from the same manufacturer. But apparently I'm gonna have to be mindful/vigilant on finding and stocking up on what works with my setup.

 

[sinister]

Friends don't let friends buy plastic magazines.

 

[BAMAboy18]

Friends don't let friends buy plastic magazines.

So, I did buy a steel 10 round CPD mag for bench shooting. It turned out to be one that wouldn't lock a bolt back, with a regular or Strike industries enhanced catch. I will find something that works and stock up. So far all I have are a couple of P-mags that seem to work for me. Hey, I'll admit I'm an AR noob, but my ignorance is being displaced all the time...

 

[mettee]

If you get metal mags, go KAC or LaRue, those are the most expensive choice. I also have/use a 10 round E-lander(I think, it's not marked) they are cheap but the ones I have run 100%. The spring tension is heavier in all of the above over pmags, I think that's a feature to make sure is present in your mags. Your bolt speed might be just slightly to fast for a weaker mag to pop up enough to engage the catch.

 

[bfoosh006]

@DIYguy​

Consider trying a D&H mag as well.
https://dh-tactical.com/7.62x51-Magazine/
https://dh-tactical.com/6.5-Creedmoor-Magazine/

You said it is a PSA build, are you using a PSA lower as well ?
Have you tried loosening the mag catch/ tightening the mag catch ?

FWIW, all 4 of my en II, PSA PA10/65's run Magpul's, IMI, D&H (both styles ) and Lancers ( those have very stiff springs, and the rounds tend to drag on the BCG when using them. )

Mine, Gen II lowers, didn't like the C-Products

 

[bfoosh006]

And.. can you post a photo of the P-Mag inserted in the separated lower... super weird the BCG is dragging on the mag, but won't grab the round.

BCG locks back via the charging handle and a single fired round ?

 

[gunsnjeeps]

Funny this thread resurfaced. I had a similar problem at the range this summer and fixed it a few weeks ago. The Magpul BAD rubs on the PSA lower and causes all kinds of drag between the bolt stop and the bolt carrier group.

Shot great. Got some mags and put a BAD on it and bought some ball ammo and it wouldn't run a magazine. Put it up for a while and got it out last month and noticed the bolt release wiggles a little fore and aft and it causes the BAD to drag on the frame. Took the BAD off and fixed everything.

 

[Zoomie]

When I built my M110 clone off a KAC receiver set, the performance was flawless over many rounds with their steel magazines. For some strange reason I tried the polymer mags and they failed. It looked like an issue with the feed lip, but I couldn't figure it out. Never again. I lit them on fire. YMMV.

That's not necessarily a comment on steel vs polymer. It's more that I am of the mind a magazine is part of a platform, not an accessory. That's why I prefer a philosophy like KAC (and others) where the magazine is built specifically for the platform.

 

[tucaz]

Friends don't let friends buy plastic magazines.

how do you feel about the lancer mags? i had some that worked well for me. i'm still not a huge fan of plastic either though.

on a side note.....i had an Aero BGC that was wider on the bottom than the mag lips would allow to pass through on some steel ASC mags. dura mags were fine.

piecing together ar10 can be frustrating.

 

[Mike_in_FL]

Friends don't let friends buy plastic magazines.

Too late to tell the entire Marine Corps?

 

[Mike_in_FL]

I have an Aero lower that worked fine with KAC 20s and PMAGs. Since KACs are pretty much unavailable these days I bought some Larue. I had to screw in the mag latch for more engagement as they were falling out of the lower.

 

[sinister]

Too late to tell the entire Marine Corps?

I'm sure sooner or later they'll figure it out.

At least they didn't buy HK magazines.

 

[Ex E6]

As I own a few PSA & Aero lowers and also run Pmags Lancers as well as original M14 mags on occasion ,I've had Zero issues with any .

There is a generational issue Gen 1 ,2 and 3 and not exactly up on all the differences but people have complained about mismatch and latch issues .

 

[Mike_in_FL]

as well as original M14 mags on occasion

You would certainly have to explain that unless you have an Armalite 10B somewhere.

 

[Ex E6]

You are Correct ,as I examined ALL MY M14/M1 Steel mags and found two which had been altered !. Unbeknown to ME ,as I had purchased a small lot from a Pvt. party and doubtful he knew either .

So MY SR25/LR308 Pmags Lancers, Hexmags and only those two steel mags fit ,MY lowers . Original GI issued Steel mags DO NOT fit . I stand corrected .

BOLT CATCH: The SR-25 employs the M-16 bolt catch. This device was designed to stop the small M-16 bolt carrier assembly, not heavier AR-10 bolt carrier assembly. The AR-10 bolt catch is larger and stronger than that of the M-16/SR-25 to function with the heavier AR-10 components. It is designed to automatically catch the bolt when pressed upward by the bolt catch trip in the follower.


MAGAZINE CATCH BUTTON: Identical to that of the M-16, except that it is somewhat longer to allow it to protrude from the side of the wide AR-10 lower receiver.


MAGAZINE CATCH: An improved, machined catch with a longer engaging surface to capture the magazine better, elimination of a bevel to prevent excess upward movement of the magazine, and a longer shaft to span the wider receiver.


MAGAZINE: The AR-10 magazine is based on the magazine of the M14 Rifle. The M-14 magazine is well proven and available in large numbers. It is both stronger and more reliable than that of early AR-10 and similar magazines. It is made in 10 round capacity.


The AR-10B magazine does not bear a latch plate on the rear surface like that of the M-14 magazine. The lower receiver, however, has a clearance cut up the back of the magazine well to allow insertion of an M-14 magazine. A 20 round M-14 magazine can therefore be modified to function perfectly in the AR-10. This modification requires changes to the feed lips cutting a magazine catch opening cutting a slot down the back of the magazine replacement of the follower with a new follower addition of a bolt catch trip and spring a slight change in the follower spring.


The most unique aspect of the ArmaLite magazine is the follower. A top surface similar to that of the M16 magazine has been combined with a form suited to the M-14 magazine box. A patented spring-loaded plunger has been installed in the follower. When the follower rises to the top of the magazine box, this plunger pops into the track at the rear of the magazine well and trips the bolt catch, thus holding the bolt carrier assembly to the rear.


The magazine will continue to function in the M-14 rifle, but will not trip the M-14 bolt catch unless the AR-10 follower is replaced with the M-14 follower. The latch plate at the rear of the magazine (which engages the M-14 magazine catch) may be sufficiently weakened by removal of its upper half that it breaks off, rendering the magazine usable only in the AR-10.


USING M-14 RIFLE MAGAZINES: The AR-10B magazine is based on the proven M-14/MlA rifle magazine. A good quality metal 20 round M-14/MlA magazine can be altered to work perfectly in the AR-10B. U.S. GI and imported Chinese magazines are acceptable. Commercial metal magazines with blue finish or pressed latch plates require replacement of the shell. Fiberglass magazines (i.e. Thermold, etc.) are totally unsuitable for conversion.


ArmaLite sells 20 round magazines when available. ArmaLite will provide converted magazines for a fee or on a 2-for-1-exchange basis. Magazine conversion kits allow a customer to convert all metal M14/M1A magazines and metric FAL magazines to AR-10B series magazines.


MAGAZINE INTERCHANGEABILITY: 10 round AR-10B magazines and converted 20 round M-14 magazines will not work in early AR-10/AR-10A rifles, or in the current SR-25 rifle. Magazines for those rifles will not work in the new AR-10B series rifles. Unless converted with the reversible magazine conversion kit, M-14/M1A magazines should not be used in the M-14 or M1A after modification.

https://www.biggerhammer.net/stoner/sr25var10/ar10vsr25.html