SBR problems

General Firearms NFA
1

So my SBR isnt liking anything but XM193 or M855(62gr Green Tip)

I had a bunch of Remington UMC 55gr but my SBR would not cycle with them at all. Especially with the H2 buffer. Hell wouldnt even cycle with the H2 buffer period, so Im using my standard buffer that came with the lower originally.

I thought maybe the buffer spring wasnt strong enough anymore, so I got a new one, but still the same problems. H2 buffer will work for maybe 10 rds and then not cycle at all. I put the light buffer in and it still does the same thing.

The strange thing is I would have to shoot half a mag of M855 62gr thru it before it would even work with regular XM193 55gr.

But like I said it will not work at all with anything other than actually 5.56x45 ammo.

Heres my setup(well the parts I think are needed to know at the moment)

Noveske 10.5
BCM BCG
standard carbine buffer
Magpul Maglevel mags

2

Can you be a little more descriptive? Is the gas block pinned or clamped on? Have you checked the bolt carrier group really good? Gas rings, gas tube, etc… Sounds like there is gas escaping somewhere and that’s why it is inconsistent.

3

I had a similiar experience with my SBR where XM193 ammo was the only ammo that would work. Like Iraqrunz said, gas is escaping somewhere.

The way that I fixed my SBR to cycle the bolt back and to use various ammo was replacing the gas key. I would also inspect your whole gas system to make sure everything is correctly installed.

Good luck!

4

it should all be fine, the gas block is pinned and clamped(the gas block came with the Noveske barrel)

I would assume the gas key is fine as Ive heard nothing but good things about BCM products. Never occured to me, but I could try the bolt from my SPR in here(its a factory bushmaster bolt). If that solves the problem then Id say theres something wrong with my BCM BCG.

5

I had the front bolt in my carrier key snap. The carrier still felt tight, but it was leaking gas bad enough to create short strokes.

Swapping the bolt groups is a good way to eliminate the BCG as the culprit.

6

jw,

I would get a carbine or H buffer and try them first. You need to go about this methodically so you aren’t chasing your tale. Get the other parts first so you can swap stuff all at once.

FWIW- I have a BCM 11.5 upper and am using an H2 buffer and a some spring that I got from GandR. It runs flawlessly suppressed and un-suppressed as markm can verify.

7

I have a Carbine buffer in there now and its working fine EXCEPT for it will not shoot standard .223, runs anything 5.56(ie 55gr XM193 and 62gr M855). Only time it doesnt shoot is with is .223(only tried Remington UMC 55gr).

8

Remington UMC is known to be weak if I recall correctly. Try and get some small batches of other ammo and see what happens.

9

thanks, was starting to wonder about the UMC, since Winchester “5.56x45” ammo, XM193 and M855 all worked perfectly.

Next question. Read on here that a standard carbine buffer would not work with a SBR. Thats the only thing I can get to work, but the felt recoil is much greater. I have a H2 buffer that I had bought for this SBR project and it will not allow the gun to cycle.

10

Do you have a full auto carrier? Use an H buffer instead of an H2. My SBR would not lock back 100% with carbine or H buffers. I added the H2 and it was golden.

11

honestly not sure. I ordered my BCM carrier group from Grant. So Im not sure if that is a Full Auto BCG or not.

12

Probably is. You can tell by reading through the stickies that show what a semi and auto carrier look like as well as the variations.

The face of the buffer is how you can tell if it is carbine, H, H2, H3.

13

Is it short stroking? I had the same issues, and had to get http://www.spikestactical.com/z/index.php?main_page=product_info&cPath=104_97&products_id=201&zenid=4mm88veb13nqvh29rs1masptc1

problem solves, my sbr is 10.5 spikes with FA BCG, standard springs, and milspec trigger from stag.

14

My CMMG 10.3" had a little trouble with Prvi 5.56 at first, but then began working 100%. I works 100% with IMI 55gr FMJ 5.56x45 (Winchester Q3131A), and Federal XM193. Winchester Q3131, Remington 223Rem 55gr FMJ, and UMC 223Rem 55gr FMJ are all too weak to cycle the action. Since I know it works with the three types of 5.56x45 that I have, I’m happy. Here’s a video of my first trip to the range with it:
http://www.youtube.com/watch?v=3MPTBfvt5pk

15

Ive pretty much decided that unless it gives me anymore problems, its fine since its shooting with XM193 and M855. Ill just shy away from Rem UMC .223, as I do believe its shit ammo.

16

What if the SHTF and you don’t have access to that ammo? If it were me I would rectify the problem correctly. We aren’t talking about bank braking parts here.

17

Exactly. JW, your gun is near functional threshold. Get it going with the light stuff to be sure you’ve got plenty of margin.

18

Im going to try out some other .223 loads, but I mostly have started to do handloads, to XM193 specs, I have around 4000 loaded and another 5000 to make, plus I have 3500 from factory XM193 and 1000 M855 here on hand. I really dont have the money at the moment to spend on anything other than what needs to be paid. After that, I have many gun projects, including this one.

Im still going to try a different BCG to see if that helps any.

19

jw,

In all honesty if you can’t afford to get another buffer then you have much bigger problems. Buy an “H” buffer and try that. If it doesn’t work then contact me and I will buy it back from you.

I highly discourage you from using handloads to check your weapon. Go to the local store buy a couple of boxes of PMC, couple boxes of some Prvi Partizan and try it out.

20

What an H buffer go for these days? 20 bucks? That’s way cheaper than a new BCG. Is there some sort of emotional attachment you have to the H2?

edit: Sorry, that was a cheap shot. But seriously, I would go for the H buffer and maybe measure your spring to make sure you have the right one.