Tight mag well in CMMG lower

[grousemaster]

I recently completed a build on a CMMG "blem" lower. Some of the pins were a pain in the butt to install, and I ended up having to "squeeze" down a couple roll pins to get them to fit. All is well with the lower parts kit installation, however, some mags don't drop free. P-mags are a no-go and certain brands of metal mags don't drop free. Any cures to this issue that any of you have had success with? It was an inexpensive lower that I don't plan on returning, but I am disappointed that CMMG sent out lowers that are not dimensionally correct.

File? Sand paper? Any insight would be helpful...

[onebohemian]

Years back when S&W took in house its AR manufacturing (away from Stag), some of the first lowers it produced had this problem. Pmags wouldn't drop free due to their ribs, but GI metal mags were fine. Back then, there were folks on the net that were using metal files, finishing sandpaper, and reblue chemicals to open up the one side of the magwell that was rubbing on the mags. In those situations, it would have made more sense for the owners to file down the ribs on the pmags but to each their own. Your situation sounds much worse if you are having metal mags stick too. Can you see inside the mag well where exactly the magazines are sticking? Is it upside on the sides, or just toward the opening?

[grousemaster]

Years back when S&W took in house its AR manufacturing (away from Stag), some of the first lowers it produced had this problem. Pmags wouldn't drop free due to their ribs, but GI metal mags were fine. Back then, there were folks on the net that were using metal files, finishing sandpaper, and reblue chemicals to open up the one side of the magwell that was rubbing on the mags. In those situations, it would have made more sense for the owners to file down the ribs on the pmags but to each their own. Your situation sounds much worse if you are having metal mags stick too. Can you see inside the mag well where exactly the magazines are sticking? Is it upside on the sides, or just toward the opening?

Feels like it's getting the squeeze from all sides, but only slightly. All mags work, but some don't drop free. Certain brands have no issue dropping free (and I happen to have lots of mags that DO work fine in this lower)....I have no issue sanding it, but is removing the finish going to promote corrosion?

[Hmac]

Sounds like an out-of-spec lower receiver...always a potential problem when buying firearms parts from lower-tier manufacturers. I'd start by contacting CMMG. If they won't step up, at least the gun is still functional. Magazines dropping free is nice, but a lot of carbine instructors recommend grabbing it and stripping it for a reload anyway.

[grousemaster]

Sounds like an out-of-spec lower receiver...always a potential problem when buying firearms parts from lower-tier manufacturers. I'd start by contacting CMMG. If they won't step up, at least the gun is still functional. Magazines dropping free is nice, but a lot of carbine instructors recommend grabbing it and stripping it for a reload anyway.

Definitely out of spec, that was apparent 10 minutes into the build. However, it functions fine. Is CMMG really considered "lower tier"? Lower than DPMS?

[Shawski]

Tight mag wells are a commonly reported problem with the CMMG blem lowers. I could think of a few other things that would be worse than just a tight mag well. I vote file or sand it a bit.

[The Lance]

7075 T6 aluminum is not susceptible to corrosion as it has been chemically treated and equalized. Unless it comes into contact with acids or caustic chemicals.

[Hmac]

Sounds like an out-of-spec lower receiver...always a potential problem when buying firearms parts from lower-tier manufacturers. I'd start by contacting CMMG. If they won't step up, at least the gun is still functional. Magazines dropping free is nice, but a lot of carbine instructors recommend grabbing it and stripping it for a reload anyway.

Definitely out of spec, that was apparent 10 minutes into the build. However, it functions fine. Is CMMG really considered "lower tier"? Lower than DPMS?

My opinion, I'd put them on par.

[Inspiribomb]

I recently completed a build on a CMMG "blem" lower. Some of the pins were a pain in the butt to install, and I ended up having to "squeeze" down a couple roll pins to get them to fit. All is well with the lower parts kit installation, however, some mags don't drop free. P-mags are a no-go and certain brands of metal mags don't drop free. Any cures to this issue that any of you have had success with? It was an inexpensive lower that I don't plan on returning, but I am disappointed that CMMG sent out lowers that are not dimensionally correct.

File? Sand paper? Any insight would be helpful...

I too have a CMMG "blem" lower that I have yet to build up. I wil check my Pmags in the magwell when I get home tonight and report back...

[Scoobyvroom]

7075 won't corrode, the surface with oxidize a bit. Best bet is to use 400 grit emery sandpaper. I use this all the time to lap the high spots off of hardcoated parts we produce. Wrap it around a flat piece of wood and go at it. Also depends on how much you need removed. Using the method above it will take a bit. Hardcoat is a funny thing, It likes to build up along edges.

[FJ540]

Once you remove the anodizing, it will oxidize almost immediately. That's not a bad thing either - it's what the anodizing was, but not as thick. Aluminum is sort of "self healing" in nature.

Type 3 should give you a .002 oxide layer per surface, so you can open it up a bit with some fine sand paper (wrap a tight mag with it) and potentially not break through it.

[kerns bbo]

I also built an ar out I'd a ccmg blem lower which was recently purchased. I ran into many assembly problems, as well as a very tight mag well. After 300 rounds or so either all my pmags or the well has loosened up and the mags slide in and out without problem.

[sgruenhagen44]

Just a thought... ever think of trying to modify the mags? I know you said it was a cheap lower but USUALLY mags are cheaper to replace than a lower so yea. But that's just me, I'm always pretty fearful about altering my guns.

[FJ540]

Just a thought... ever think of trying to modify the mags? I know you said it was a cheap lower but USUALLY mags are cheaper to replace than a lower so yea. But that's just me, I'm always pretty fearful about altering my guns.

Chicken!

[timwarner]

magpul ETM mags?