Magazines will not lock up in AR 15

[KHickam]

I have built a new AR 15 using quality parts - the lower parts kit was a Spikes - - gun shoots fine - works fine.

However, when using Red Jacket or Blackhawk and USGI aluminum magazines it locks in fine - However, when using a P-Mag or Troy or Tapco plastic magazines - the magazines will not lock into the magazine well - I tried dremeling the magazine to open up the catch slot/hole and it still will not lock in - I even backed out the magazine catch lever a bit to maybe give it more bite - not having any effect.

Suggestions?

[OlBill]

Will they lock up if you load them with an open bolt?

Will they lock up empty?

[KHickam]

No I tried that too - thinking they needed 28 rds instead of 30 rds - most times they will not lock in empty either - but metal magazines have no problems

[OlBill]

Interesting. Have you tried them in a buddy's gun?

I would try that. If they don't, I'd send one back to Magpul and have them check it out. If it does, you'll know it's your rifle (probably].

Sorry I couldn't be more helpful.

[psijac]

Are they older mags? Plastic will always stretch out a little. Buy a brand new pmag and see if that works

[RogueUSMC]

Gen 4 Pmags have had issues with some receivers. I have yet to hear of any problems with the Gen 3 Pmags. The Gen 4 Pmags are trying to be cross-platform from what I understand. There has been instances where the little 'shelf' that keeps the mag from going too far in and interfering with the action on some platforms that are not AR platforms. The Gen 3 mags don't have this little stop.

[couzin]

No problems with metal or plastic on any of my builds. Here is what I would check: As suggested, will the magazine (unloaded) lock if you remove the bolt; Will it lock if you separate the lower; Have you tried giving the magazine a smack as it goes home; Do any of these thing lock up but when loaded with ammo refuse??? I have heard of using the anti-tilt followers giving some users problems. But since you say loaded metal mags do lock up (and I suppose run?), my first thought would be you have a slightly mismatching upper and lower. Get that bolt out of the way and check the feed ramp - if the upper is protruding a little it could be catching the round because of the geometry of the plastic mags. Just a SWAG...

[KHickam]

Checked everything I could think of on the gun - I lived with this weapon system for most of my career - and literally lived with it on at least two deployments

PSA is having a weekend sale on magazines $6.99 for aluminum magazines so I ordered 5 of them for it.

[OlBill]

It doesn't sound like the gun to me.

[AJSully421]

You mentioned that you backed the mag catch out... try screwing it in as far as you possibly can. One more turn will make a big difference. Take a bic pen or something and push hard on the button and see if you can pry it around one more turn and in to the slot. If the catch post is sticking out past the button (very hard to do unless something is not correct, then you have it too far, back it off by one turn. If it is flush or just a little bit inside the button, that is correct.

Do this and try again.

[KHickam]

Yes, I tried that too - backing it out - really tightening the magazine catch screw through the magazine button - no go with polymer magazines - not a problem with aluminum and steel magazines - I have 5 magazines that are metal on order to go with the 5 I have from back in the day - buying surplus magazines near base for $5 near the end of my career.

I may just get another magazine catch and button and try it - after all they are not that expensive and if that doesn't fix it having to shoot all metal magazines is not that big of a deal the cost is very similar to polymer.

[Jketchum]

tuned in.
I have 2 surplus steel mags that do this. even though I don't see anything wrong with them ive set them aside not to be used. All my other mags both steel and P-Mags work fine.

[KHickam]

New magazine catch fixed the problem.