Originally Posted by bug_eyedmonster
I recently got a CMMG 308 lower. Can anyone tell me more specifics about this? I've been reading here, regarding the mag catch and issues with the bolt catch? Can someone tell me more in detail about these problems? I was also thinking about getting a DPMS (assembled) upper, but it seems my barrel options are limited, unlike my MEGA build. Sorry, I have been working on my 5.56 builds, and just getting back into the .308 world. Thanks in advance, I'll hopefully post u some builds here soon.
There is one question I would have to ask you regarding the CMMG .308 lower first, is it the MK-3 (older), or MK-8 (newer) model?
MK-3 looks like this
if you have the MK-3 (their older model) it does have some issues, but I am pleased with it overall.
1ST ISSUE –
the front take down pin has just a hair to much material in front of it to allow the upper to hinged like an AR-15, it has to come up. here is my conversation with Tech support:
Me: I have a MK-3 .308 lower receiver and I realized that the material around the front pin hole is not the same which makes it so that you cannot split the upper and lower by removing the rear pin and rotating the upper and lower in opposite directions (like opening a double barrel shotgun I guess) for cleaning or whatever. It might be confusing in the way I'm trying to explain, so if that's the case, just ask for specification. This was the case with all the uppers I tried on this lower. They fit nice and snug with both the pins in but they pretty much just come apart straight up and down.
I tried to get the upper and lower open like this by sticking in the front pin and forcing it by rocking it back and forth which shaved off a little bit which wasnâ t the best idea, but oh well. I then used some Aluminum Black Metal touch up, but it still looks bad from up close as can be seen in the pictures.
Is there anything that can be done easily to have the extra 1-2 hundredths of an inch taken off and then re-coated to look better?
Tech Support: Our older .308 Lower design was not machined to actually be hinged like your wanting, our new design is. There is good news-I can get your lower and machine it for hinging like our new ones and have it re-anodized and tefloned for you. Your cost for that would be $60 for the machining and $35 for the re-coating, plus shipping costs. Let me know if you’re interested. – CMMG Tech Support
I ended up getting it taken care of somewhere else, but they were helpful.
2ND ISSUE –
my magazine would fall out randomly (before I had an upper receiver) I tried a couple of thing which both worked. The first was to put a very small shim between the right side of the bullet button and the bullet well (in the front of it if you’re looking down range)which made the mag catch stay in. the second solution came from my friend had a Raddlock gen-x bullet button and was bummed because he couldn’t use the mag release tool that Phase 5 Tactical makes
so he traded me for my regular Prince bullet button. If you don’t install the rubber gaskets that it comes with, and tighten it down, the Raddlock doesn’t have the same issue.
And, for the MK-3, as far as I know, any DPMS style upper will work (Armalite, and Rock Rivers will not) I built a SASS upper and I love it.
The last issue you mentioned was problems with the bolt release/catch? I haven’t had any issues, but I would recommend the Phase 5 Tactical Extended Bolt release
if you’re looking for one. Here’s a picture of mine.
MK-8 looks like this:
if you have the MK-8, I’m not much help, but after talking to CMMG about my MK-3 issues, they mentioned the MK-8 was the replacement model for the MK-8 but took a different magazine but that’s about all I know.