I took my new CMMG 10.3" SBR to the range for the first time. After receiving an upper with the wrong barrel and a loose handguard cap, they finally fixed things, although it seemed to take forever. I seriously doubt if I’ll ever order from them again, but I think that I ended up with a quality rifle in the end. Here’s a picture:
I went to a range to shoot it for the first time. Here’s a video: http://www.youtube.com/watch?v=3MPTBfvt5pk
I used 30rds of the Prvi in the first mag. There were four failures to feed from the magazine, mostly at the beginning. Then I shot 20rds of the Q3131A. It felt like it had a little more punch to it and the rifle didn’t have any function issues. A friend then shot 30rds of the Prvi without any problems. Another friend then tried to shoot 30rds of Q3131, but he gave up after shooting 4rds. The rifle simply wouldn’t feed the next cartridge from the magazine. Finally, I fired 3 more 30rd mags of Prvi without any problems.
Am I correct in thinking that the four failures to feed using the Prvi ammo that I experienced when firing the first mag were probably just break-in related? Am I also correct in thinking that the Q3131A is a little hotter than the Prvi? What’s up with the Q3131? The box was labeled 5.56.
I’m no expert, but have shot the prvi and had no problems.
I’m assuming you were using pmags?
Break in should not be an issue. FWIW, my LMT 10.5 shot perfectly with a mix of prvi and reloads (made by me and pretty light loads). No “break in” required. For that matter, I don’t remember ever having a break in period with any of my AR’s.
I used a pmag a couple of times. The rest were USGI with Magpul followers.
Break in should not be an issue. FWIW, my LMT 10.5 shot perfectly with a mix of prvi and reloads (made by me and pretty light loads). No “break in” required. For that matter, I don’t remember ever having a break in period with any of my AR’s.
I agree, but find it odd that the only malfunctions with the Prvi were in the first half of the first magazine. The Q3131 not working at all is a big clue, but I’m not sure what it means.
It means you should probably send your rifle back, (again)…
Maybe it’s just me and perhaps the AR and SBR experts will chime in, but unless it was just the video, something in that gun does not sound right…When you pull back the charging handle, it sounds odd. Also, what’s your buffer set up and what kind of bolt are you running?
RULE 4
Contact The Manufacturer or Dealer First – Internet forums have a large global audience and unsubstantiated or ill-informed comments will affect the livelihoods of a lot of hard working people in the industry. If you have an issue with a manufacturer or dealer that you would like to resolve, we ask that your first contact them to resolve it.
What was CMMG’s response?
Having said that, what procedure did you use to clean and lube the BCG and what lube was used prior to firing the gun? You did lube the BCG, right?
Regardless of any issue with the mags, from what I see in the video it could be that either the gun is sprung too heavy, you are using a buffer that is too heavy, little or no lube on the BCG, the gun is undergassed or a combination of all of the above.
David, thanks for the lecture, but if I thought something was definitely wrong with the rifle, then I would have certainly contacted them. However, since I suspect that it may be break-in and/or ammo related, I figured that I’d ask some knowledgeable people here for their opinions. Perhaps SBR’s are especially sensitive to the ammo used? I don’t know. None of my other AR’s have ever required a break-in period, but given that the rifle began functioning fine with the same ammo, is it safe to say that it’s OK now? Is Q3131 underpowered, and therefore, sometimes problematic in SBR’s? If I did call CMMG and ask them what they thought, what do you think the answer would be? I’d bet a dime to a dollar that they’d say what the vast majority of other manufacturers would say. There can be an initial break-in period and don’t use that ammo. I could be wrong, but I don’t think that rule was meant to preclude the posting of a couple of questions about the initial function of a new rifle.
Having said that, what procedure did you use to clean and lube the BCG and what lube was used prior to firing the gun? You did lube the BCG, right?
I cleaned and lubed it just like I do all the rest of my AR’s. Yes, I lightly lubed the BCG group with Shooters Choice Rust Prevent. I’m assuming that SBR’s don’t require anything special.
Regardless of any issue with the mags
The mags I used have worked 100% in several other AR’s, so I’m confident if there is a problem, it is not mag related.
could be that either the gun is sprung too heavy, you are using a buffer that is too heavy, little or no lube on the BCG, the gun is undergassed or a combination of all of the above.
If it’s the recoil spring or buffer, then I do need to contact CMMG because they supplied both. I’m confident the rifle was lubed properly. You don’t think that simply needing a little break-in (sharp edges or rough spot on something) was the initial problem? What about the Q3131?
no lecture intended. Simply pointing it out. The other things I pointed out such as type of spring, buffer, and lube were not mentioned in your original post and I thought they may help other in trying to diagnose your problems.
In my experience, some ARs require break-in and some don’t. There isn’t really any concrete rule about it as far as I’m concerned. I’ve seen some low-end ARs run great right out of the box and I’ve seen some that needed at least a couple of hundred rounds before things smoothed out. I’ve seen some high quality ARs do likewise. My 10.5" LMT was tight as hell for about a hundred rounds or so, but has run great ever since.
On topic, from watching the video, when you’re using the charging handle the gun sounds kind of dry (as in underlubed) to me. I run my ARs pretty well lubricated (wet, but not dripping wet - and I use Slip2000) but it seems to me that SBRs like a bit more lubricant than carbines or rifles. I would suggest lubing it more than you usually do, and trying it again.
Personally I’ve had no problems with Q3131, so I’m not sure why you’re having particular problems with that.
To mirror others try more lube and different ammo.
I don’t think Q3131 is renowned for being high-end ammo. Mags sound GTG.
That being said. My LMT 10.5 ran fine out of the box with USGI and PMAGS and using UMC 55gr, XM193, Black Hills 55gr FMJ, and M855. Lubed fairly heavy with Slip200 EWL.
It could be that the buffer spring inside the buffer tube was dry. I don’t recall if I oiled it again before I shot it or not. I’ll take the buffer and spring out to make sure everything looks OK. I do recall noticing that when I shot the Q3131A, the buffer spring seemed a little louder. I don’t own any Q3131, so I guess it’s not a problem, but I’m still curious what caused it not to work. I do have a chronograph, so I’ll take it along with the Prvi, Q3131A, XM193, and I’ll trade my friend for a few boxes of Q3131 as well. Velocity doesn’t tell you how much pressure there is, but there is a strong correlation. And yes, I’ll heed the advice given and lube it up more. Thanks!
I have shot the Q3131A for several years w/o issue in Colt, BM, RRA and S&W weapons.
This ammo is made by IMI under the Winchester name is mil-spec and NATO marked…std 55gr fmj load with advertised specs of around 3250 fps out of a 20" tube. All that I have ever purchased/used has been clean, sufficiently accurate, desirable ammo.
I have shot a lot of and still have some IMI M855 that has always been fine as well.
Like others, check your lube job and buffer/spring set up. Most likely, there is where your problem lies.
I pulled the buffer and buffer spring out. I noticed that the ends of the buffer spring do not have a reduced diameter like the one in my Stag AR15. As a consequence, the buffer spring does not retain the buffer. It just falls right out. The end of the buffer spring in my Stag AR15 is tight around the buffer. I have to pull and twist it to get the buffer free from the spring. Should the end of the buffer spring have a reduced diameter or does it not really matter?
I have the same rifle. I cleaned the rifle when I got it, lightly oiled everything, and put it in the safe. The first time at the range, my first mag had several malfunctions (using Wolf). I checked the bolt and it was wet, but I went ahead and liberally lubed the bolt. No more malfunctions for the rest of the day. It was frustrating at first, but I know better. You can never have too much lube in your AR, especially the DI models.
I took it back to the range today and fired 60rds Prvi 55gr FMJ M193, 50rds Federal 55gr FMJ XM193, and 10rds Remington 55gr FMJ through it. It ran 100%! I’m going to assume that it was just a break-in issue unless something else happens.
I also took my Stag M4 clone (with Sabre 14.5" barrel) and was using a chronograph for the first time. Here are the average velocity results:
Fed 55gr FMJ XM193 in Stag AR15: 3036fps Standard Deviation: 15fps
Prvi 55gr FMJ M193 in Stag AR15: 3050fps Standard Deviation: 23fps
Rem 55gr FMJ in Stag AR15: 2872fps
Fed 55gr FMJ XM193 in CMMG AR15: 2807fps
Prvi 55gr FMJ M193 in CMMG AR15: 2789fps
Rem 55gr FMJ in CMMG AR15: 2638fps
Fed 55gr FMJ XM193 velocity difference: 229fps
Prvi 55gr FMJ M193 velocity difference: 260fps
Rem 55gr FMJ velocity difference: 234fps
There was one guy in the video that was holding on to the magazine as he shot. I wonder if he was pulling back on the mag enough to cause the problem? I bet it will work fine now.
Quite probably an issue as the magazine is not a hand-hold. Could have been just enough effect on the angle to affect feeding.
I did just watch your video for the first time as could not get onto youtube earlier… The short stroking could have been the ammo, but also check your carrier key on the BCG and ensure the bolts are tight and it is staked properly. If the carrier key is loose, you could have too much gas escape before pushing the BCG back. I had that happen with a Bushy BCG. It started by only doing it 1-2 rounds a magazine but quickly progressed to making my rifle an expensive single-shot carbine (putting me in last place at the competition this occurred at). I wrongfully assumed my gas tube was probably plugged but ended up being the carrier key.
And of course, plenty of lube. It should be VERY wet.
