First Build - Little Help: Tight Magwell

[koji]

Hey folks,

I've been lurking here for a while learning everything I can about AR's. I'm new to AR's, but I've had a lot of fun so far with my M&P15 (~3,000 rounds through it in the past 5 months).

About a month ago I decided I wanted a second AR and rather than buying it I decided to build it just for giggles. I completed the build today. The upper is a BCM Middy with a DD-Lite rail. The lower is from CMMG. I used a Bill Springfield trigger and a DPMS parts kit for the rest.

The problem I'm having is that the magwell is either way too tight from the factory, or I screwed something up somehow. Everything on the lower functions as intended except the mag release. Here's the details:

1. I push the mag release, and the magazine does drop a quarter inch or so. The mag catch has released at this point because I can pull the mag free by hand.

2. The mag will not just drop out of the lower via gravity.

3. When I insert a new mag there's a lot of friction. It doesn't just slide in easily like on my M&P. This leads me to believe that the problem wasn't my assembly but rather the lower itself.

I've searched, but I haven't found this particular problem discussed and I have absolutely no idea how to go about fixing it. Any and all help would be appreciated.

Thanks!

[Thermodyn]

What type of mags are you using? In my experience, GI mags seem to work well across the board with just about any lower, but Magpul P-mags don't drop free consistently. They drop free out of my LMT, but do not fall free of my LAR lower, or my brothers Colt LE6920.

[koji]

Ugh. PMAGS are all I have and I've got a decent stock of them. If I need to stock a different set of magazines just to run this lower I'd rather A) mod the lower or B) get another one.

[spamsammich]

Don't mod the lower. Sand the tabs down on the pmag that make the fit tight. There are two small bumps along the spine of the pmag that are making it fit tight in your magwell. Mod those.

[M4arc]

Ugh. PMAGS are all I have and I've got a decent stock of them. If I need to stock a different set of magazines just to run this lower I'd rather A) mod the lower or B) get another one.

Out of the seven lowers I own my PMAGS only drop free from one of them. It's quite normal from what I've seen. Sand the mags down or sell them and buy some USGI mags.

[koji]

Thanks for the feedback. This is clearly a problem I missed when selecting PMAGS. I had no idea it was that common of a problem. I'll break out the dremel and get them fixed and leave the lower alone.

[M4arc]

Thanks for the feedback. This is clearly a problem I missed when selecting PMAGS. I had no idea it was that common of a problem. I'll break out the dremel and get them fixed and leave the lower alone.

I believe it's recommended that you use sandpaper. A dremel might be overkill and take too much off.

[LOKNLOD]

I believe it's recommended that you use sandpaper. A dremel might be overkill and take too much off.

Sandpaper works, and I used a small flat file to good success as well.

[koji]

I believe it's recommended that you use sandpaper. A dremel might be overkill and take too much off.

Thanks for the recommendation, I've got plenty of both. I make a lot of stuff out of fiberglass and carbon fiber so my Dremel skills are pretty solid but I'll try it a couple of ways and see what works best for me.

Just to be clear, what I need to remove are the two upper tabs on the forward facing spine of the magazine - correct? There are two tabs on the backside as well but they're far enough down I don't think that could be the problem.

I'll run a search too to see if I can find the answer on my own. :)

[JohnVassilakos]

My PMAGs are really tight in my MEGA Machine lower also. GI mags are no problem for it though.

[cyclone72]

I have a CMMG M4LE and have some bad fitting issues with P mags, I can barelt get them in at all. Guess a fine grit sandpaper will have to do.

[ziggiey]

I stick with USGI mags, work in everything. 20 rounders are all I need.