AR guys: NFA poly lower help? Can't install mag catch

Don't some of those polymer lowers require some reaming and such.

Ideas?

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I'd use my vertical mill to open it up.

Barring that, very careful hand filing.

Just curious, but why SBR a poly lower? To me, it doesn't seem like a great idea to tax stamp a budget gun.....

I don't know if this is your problem, but sometimes lowers, particularly cheaper ones, are out of spec. It sounds as if it simply is out of spec.

I will note that some polymer lowers that I have experience with like the cav arms lowers tend to be a little tight in places initially and wear in a bit with use. that is different than simply not fitting at all though.

As to ideas, I'd say there are a couple of possibilities.

1) try a different catch, although it sounds like this wont make any difference because it sounds like it is not a matter of the catch being out of spec. (you might also check your mag catch in another lower).

2) Contact the seller and/or manufacture.

3) Carefully remove material (in theory from the mag catch or the lower) until it can fit. I agree with the above advisos about 1. not using a dremel and 2. researching it more before you do something you cannot undo.

4) Leave it un-built, keep it or sell it and learn a lesson about buying cheap plastic AR lowers. I have learned my own lesson about cheap lowers, having previously gotten two forged lowers that were out of spec, one very seriously so, I've learned a bit of that myself.

A quick google search turns up other instances of parts not fitting in real well. See e.g. http://www.ar15.com/forums/t_3_4/601444_NFA_lower__mag_release_button_will_not_go_in_.html&page=1

I was researching these lowers last week and found this issue. There are lots of posts on ar15.com from folks with the same issue with this lower. Search over there for some tips...I believe there are some YouTube videos that address it too.

Good luck & post up pics when you get that baby built!

In this case I think NFA = New Frontier Armory not National Firearms Act.

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Ah. Should have thought of that. Duh!

I have one of the those lowers and they definitely require hand fitting of most of the lower parts kit. Use a fine small file set and take your time.

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I would be more inclined to send it back if they are paying shipping both ways. If it was going to cost me any money I'd probably do it myself. It's not like it is particularly challenging work. Shipping that thing there and back would cost almost as much those poly lowers will be selling for again soon.

The mag catch won't slide freely into the receiver so I can thread the button on

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This sounds backwards! You push the spring and button all the way in and thread the catch onto the button, once the thread starts, you pull on the catch as much as you can and rotate it to screw it the proper depth into the button, letting it slip into the slot on the last revolution.

Don't "open" anything up! the catch slot prevents the spring from pulling the catch all the way into the mag well, which would interfere with magazine insertion if it did.

I have an ATI poly lower (dedicated 22 LR build), and I had no problems with the mag catch. I had a heckuva time getting the bolt catch installed. Every time I put one of these in, I always tell myself that it's my LAST AR build!!! Until the next one, of course...

I wouldn't modify it myself. It's defective. Send it back and let them fix it

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Probably not defective, more like out of spec.

I bought one of the poly lowers from ATI/Omni for a lightweight AR build last year. Luckily I bought a complete lower instead of a stripped receiver.

I can tell you for sure that some areas are out of spec. The holes for the front pivot pin and rear takedown pin are very tight almost to the point where you have to kinda hammer the pins in and out of place when assembling/separating the receivers.

The magazine well is also tight; magazines don't fall freely like they do with aluminum lowers. I bought this poly lower to T&E and build a lightweight AR pistol, not as a primary rifle. Other than that, it has functioned fine with 5.56 and 300BLK uppers.

So you're saying that the long piece of the mag catch (that goes on the left side I believe) won't go in at all? If thats the case, then its definitely out of spec.

I'm not sure if you feel comfortable filing it out just a bit, or just send it back for warranty. I would recommend to at least call NFA and see what they say about your issue

The last batch of NFA lowers seem to be a little tight in the mag release area. I built several for customers last week, and had to remove a little bit of material for smooth operation. A utility knife works great, just shave a hair off both sides little by little until you have enough clearance.

I just put an NFA lower together, had the same problem with the mag catch. I used the tip of a knife to slowly scrape away shavings of polymer from the tight area and kept checking the fit until the catch moved freely. A round file would probably be easier/faster. After you get it too fit it is no different from any other polymer lower.

Had to do the same thing on mine, and could only get the button threaded on about halfway.

Interesting reading.
Thanks for all the comments by others. I was looking at wet5her to go with a poly lower for a build. Think I will shy away and spend a bit more.

I've built 3 NFA lowers and am about to do #4 & 5, either a small file or exacto knife to open it up slightly, on their unfinished lowers there is always a small amount of fitting right there...Its not out of spec per se, its just excess poly from the mold...