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View Full Version : Is 308 CMMG Lower/DPMS Upper Bolt Supposed to Lock to the rear w/ paddle?


tacticalcity
03-04-2010, 4:38 PM
So I just finished my 308 AR Build (pics coming soon). A Cmmg Lower with a DPMS upper. Only when depressing the paddle bottom all the way down, and pulling the bolt to the rear then gently releasing it, the bolt does not lock to the rear. I have not tried inserting a magazine. So my question is? Is is supposed to be able to lock to the rear with the paddle?

Its not a big deal. 9mm builds to the same thing, so I am familiar with constantly chamber checking. Just curious if this is normal or if perhaps something is wrong.

Also, there is more play than I like between the upper and lower. Its a minor amount of movement for a 556 build. But with the 308s heavy upper and with a heavy scope on it, it just feels awkward. The ACCUWEDGE does not fit. I could probably carve it down with an exacto knife until it works. I am just curious if there are any other solutions for 308s that you guys are aware of, since the shape of the parts is different than 556 ARs.

Thanks.

neal0124
03-04-2010, 7:21 PM
Are you referring to the bolt catch? If you are, then there was another thread about the same problem. The cure was to loosen the bolt catch screw/pin. When it is too tight it will bind up and not rotate enough to catch the bolt face.

For the loose lower/upper, I'd stick with a trimmed down accuwedge. There are rear takedown pins that will pull both receivers together but it makes it much more difficult to separate the two, you'll need tools to take the receivers apart.

tacticalcity
03-04-2010, 10:50 PM
Tried loosening that screw, even loosened it almost all the way out. The bolt will not lock to the rear. Even inserted an empty magazine. Still won't lock to the rear.

9mm builds won't lock to the rear either. So it could just be that it won't do it no matter what.

tacticalcity
03-04-2010, 10:51 PM
Here is the updated picture of my collection. Sorry about the quality. I am moving, so my camera along with most of my knives, lights and other gear are in boxes. I'll take a better picture and post it once I am moved into my new place and unpack the camera.

Top to Bottom:
- Cmmg Lower/DPMS Upper 308 Win AR Precision Rifle
- Cmmg M4gery 5.56mm
- Glock 19 9mm
- Mega Machine AR15 Lower Stripped (Not sure how I am going to build it up)
- Red River Tactical Lower / Custom Built Upper 5.56mm AR Pistol (GAU-5/A Clone)
- Remington Target Master 22lr

My father has my shotgun, a 1950s Remington Sportsman 58 12ga Semi-Auto, so it is not in the picture.

http://i256.photobucket.com/albums/hh183/tacticalcity/IMG_0078.jpg

pyro3k2
03-05-2010, 2:14 AM
did you use the correct spring when installing? could the bolt catch pludger be facing the wrong way? if the bolt won't lock to the rear even with an empty mag could be a deformed bolt catch. If I recall correctly the bolt catch is the same on the DPMS 308's as is it is on the ar15, could compair the two and try diff parts from rifle you know that work correctly.

pacrimguru
03-05-2010, 8:31 AM
9mm builds won't lock to the rear either. So it could just be that it won't do it no matter what.

my 9mm build locks back consistently, every time.

tacticalcity
03-05-2010, 10:17 AM
The CProducts 9mm drop-in conversion block usually won't lock the bolt to the rear. Tried it with a few different brand uppers, none of them locked to the rear. That is what I was referring to. It wasn't a big deal, just had to do lots of chamber checks (or press checks if you're the guy from Magpul).

I emailed CMMG (since they have excellent customer service) to see if they had any information for me. The last time I had an issue with a product (a lower) they had me ship them mine and they replaced it with a new one (and were kind enough to assemble it for me).

Odds are it is the DPMS bolt. I sold a DPMS M4 upper a long time ago where the bolt would not lock to rear. DPMS replaced the bolt. But DPMS is a pain to deal with. So I wanted to see if CMMG could help me first.

Pretty sure the spring and plunger are facing the right direction. Even with the mag inserted, it will not lock to the rear. Compared the bolt catch to my AR15 bolt catch. Nothing stands out as being off.

evollep3
03-05-2010, 11:16 AM
The CProducts 9mm drop-in conversion block usually won't lock the bolt to the rear. Tried it with a few different brand uppers, none of them locked to the rear. That is what I was referring to. It wasn't a big deal, just had to do lots of chamber checks (or press checks if you're the guy from Magpul).

I emailed CMMG (since they have excellent customer service) to see if they had any information for me. The last time I had an issue with a product (a lower) they had me ship them mine and they replaced it with a new one (and were kind enough to assemble it for me).

Odds are it is the DPMS bolt. I sold a DPMS M4 upper a long time ago where the bolt would not lock to rear. DPMS replaced the bolt. But DPMS is a pain to deal with. So I wanted to see if CMMG could help me first.

Pretty sure the spring and plunger are facing the right direction. Even with the mag inserted, it will not lock to the rear. Compared the bolt catch to my AR15 bolt catch. Nothing stands out as being off.

c-products lock up for me are you sure you have the right bolt catch?

tacticalcity
03-05-2010, 11:31 AM
I sold the 9mm builds a long time ago. I remember researching it at the time and reading it was a normal issue with various 9mm builds based on your bolt and conversion block combination. It was not an issue for me, and certainly not one I care about. The bolt would lock to the rear using the bolt catch, but not with an empty magazine. Just took me a little bit to remember that detail. I read up on it at the time, and discovered it was a common and normal thing. But obviously I could careless about it, since I no longer own a 9mm conversion. What I care about is my 308 build. I want to keep this one.

Called DPMS about my 308 issue. They said it is possible they accidentally sent me the wrong buffer. Apparently the AR15 buffer is longer than the 308 buffer. So they asked me to measure it this weekend and see if it is the correct length, 2.5". Apparently if it is too long it can prevent the bolt from going far enough back to catch. I ordered an A2 complete 308 buttstock assembly from them when I ordered my custom upper. But it is possible they screwed up and sent the wrong buffer. Will know once I measure it.

It is also possible CMMG accidentally sent me the wrong bolt catch. But I doubt it. As far as I know they are the same. I emailed CMMG (my rep is out for the day) about it and am waiting for them to get back to me. Lucas, my rep, is awesome. He'll go out of his way to fix things. Sadly he is so damn popular because he always says "yes" when issues come up that he is hard to get ahold of on the phone.

evollep3
03-05-2010, 1:34 PM
bolt catch for the 308 is actually different and buffer problem could be the cause as well as the spring since there is more coils in the AR15 spring

tacticalcity
03-05-2010, 2:38 PM
Went home during lunch to test out a few of your guy's ideas (thanks for those by the way).

Ruled out the length of the buffer being the problem. Inserted a very short carbine buffer just to see if the buffer being too long is the problem. Even with the extremely short buffer it still would not lock to the rear.

Ruled out the spring and detent of the bolt being the problem because I removed them all together to give the bolt catch 100% freedom of movement and press down all the way, and it still would not lock to the rear.

Have yet to compare springs with an AR15 spring, since that is a new suggestion.

Will wait to speak with CMMG about the bolt catch itself. If I have the wrong one they'll send me a new one for free.

I'm thinking there is something wrong with the bolt. Seen it before on a DPMS AR15. But I want to rule everything out before I ship the entire rifle to DPMS.

Pretty frustrating, since you guys have offered some great suggestions and still the problem exists. Sadly it looks like the only options left (aside from the buffer spring being the problem) would involved getting new parts or sending it off to either CMMG or DPMS or worst case both if the first one says its the other guy's fault. I am not crazy about ordering parts unless I am certain it will fix the problem. So unless CMMG sends me a new bolt catch to try out for free, I am going to have to send it to somebody.

tacticalcity
03-05-2010, 2:58 PM
CMMG asked me to send it to them for examination. They will work with me (and DPMS if needed) to get it fixed. Sounds like a plan at this point.

evollep3
03-05-2010, 3:09 PM
if you take a picture of the bolt catch i can tell you right away if its wrong

tacticalcity
03-05-2010, 3:26 PM
Because my camera is boxed up (I am in the middle of moving into a new apartment) it would probably be more difficult to get you a picture than just send the darn thing back to CMMG. Got 50 boxes staked up in the living room and I am not sure wich of the 15 boxes marked office it is in, or where they all are in that pile. But I do appriciate the offer.

My rep sounded like he's heard of this issue before. He did not flat out say so, but their first batch of 308 uppers apparently had some issues. Supposedly they sorted them all out a long time ago. This lower could have been old stock a dealer on gunbroker had laying around, which would explain the low price I paid. Regardless, CMMG is going to get it sorted out for me.

tacticalcity
03-05-2010, 3:30 PM
The only part that sucks is it puts a damper on my weekend plans. I had hoped to spend saturday dialing in this rifle. No worries. I'll just dial in a different rifle. I just finished putting together a few of them. But this 308 was going to be my bench rest queen. The others are setup more for CQB.

tacticalcity
03-08-2010, 11:52 AM
Taking an exacto knife to an Accuwedge did the trick on taking out the receiver wobble. Had to carve away a lot of rubber and trim down the top in order to get it to fit, but the end result is perfect.

Still have yet to send it to CMMG to get them to figure out why the bolt won't lock to the rear.