View Full Version : SBR problems
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
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.
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
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!
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.
I would assume the gas key is fine as Ive heard nothing but good things about BCM products.
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.
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.
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).
Remington UMC is known to be weak if I recall correctly. Try and get some small batches of other ammo and see what happens.
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).
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.
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.
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.
honestly not sure. I ordered my BCM carrier group from Grant. So Im not sure if that is a Full Auto BCG or not.
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.
honestly not sure. I ordered my BCM carrier group from Grant. So Im not sure if that is a Full Auto BCG or not.
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.
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
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.
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.
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.
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.
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.
Exactly. JW, your gun is near functional threshold. Get it going with the light stuff to be sure you've got plenty of margin.
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.
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.
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.
spamsammich
10-28-09, 01:12
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.
no no, what Im saying is Im going to pull the BCG outta my other AR, which I know runs perfect with anything Ive shot. Try that BCG in my SBR. I already took the H2 buffer out as it would not work AT ALL and am running a carbine buffer from my dads Bushy M4. With the standard carbine buffer it shoots, just not Remington UMC. Im going to try some PMC and other .223 loads. all I was stating is for your "if the SHTF" comment is Im not worried about only having access to cheap ammo, as Ive got plenty of my own already. I have enough parts to pull off other guns to try and fix this one if need be that I dont need to buy anything right now. Therefore Im not going to spend money on things I dont need, when I have plenty of different things to try.
Robb Jensen
10-28-09, 07:39
Noveske 10.5" barrels usually have factory gas ports of .071". This is fine with a H buffer even with 5.56mm NATO pressure ammo. Go heavier if using a suppressor without a switch block.
You generally don't need an H2 buffer on a 10.5" barrel unless suppressed like I said or with a gas port of .076" and up.
got ya. Im still going to pull the BCG from my other AR and try it on my SBR. If it cycles with something other than a true 5.56 round(ie Rem UMC) then I have a problem with my BCG from my SBR, and I know where to look. If that doesnt solve the problem, its some where else.
Right now I am using a non "H, H1, H2" carbine buffer. Im using just a standard unmarked Carbine buffer from a S&W M&P15, which is my other AR. As of right now with that Buffer from my other AR, it will shoot just fine with the XM193, M855, and some Hornady 75gr BTHP Match .223. The only ammo I have found it will not fully cycle with(will eject the case but not chamber a new round) is the Remington 55gr UMC.
Ill try swapping the BCG from my M&P15 to my SBR and seeing if that works.
Im not trying to sound like an ass, I appreciate any and all help from you guys, hell I love this site, Ive never built an AR before and just from the advice and reading on this site, from guys like Iraqgunz and a few others I have been able to build 2 AR's from Scratch, finally learn that XD's arent that good of pistols and that my now favorite G21 SF is by far my fav hand gun Ive ever owned.
Ive just been trying to explain that I have 2 other AR's that do work that instead of buying something right away I can pull from them to try and fix the problem, then purchase parts as needed.
spamsammich
10-28-09, 12:21
Just a shot in the dark, but have you tried this lower with another upper? Perhaps there is something about the lower that is causing the BCG to hang up? do you have access to a set of gage pins to measure the actual diameter of the gas port?
Guys, I have a 10.3" SBR that seems to be on the edge like jwfuhrman's. It cycles fine with full power NATO spec. 5.56, but sometimes short strokes with the lighter powered 223Rem spec. loads. I'm having a hard time understanding why some here are recommending H buffers. If a rifle is already on the edge of short stroking, won't addinig weight to the buffer decrease the stroke? I'm thinking if anything that the weight of the buffer would need to be decreased. I think my SBR has a full auto bolt carrier. So, wouldn't changing over to a lighter semiauto bolt carrier increase the stroke?
Here's a video that shows the cases ejecting while using NATO spec. 5.56 ammo.
http://www.youtube.com/watch?v=9ziYcOrzOFQ
got ya. Im still going to pull the BCG from my other AR and try it on my SBR. If it cycles with something other than a true 5.56 round(ie Rem UMC) then I have a problem with my BCG from my SBR, and I know where to look. If that doesnt solve the problem, its some where else.
Right now I am using a non "H, H1, H2" carbine buffer. Im using just a standard unmarked Carbine buffer from a S&W M&P15, which is my other AR. As of right now with that Buffer from my other AR, it will shoot just fine with the XM193, M855, and some Hornady 75gr BTHP Match .223. The only ammo I have found it will not fully cycle with(will eject the case but not chamber a new round) is the Remington 55gr UMC.
Ill try swapping the BCG from my M&P15 to my SBR and seeing if that works.
Im not trying to sound like an ass, I appreciate any and all help from you guys, hell I love this site, Ive never built an AR before and just from the advice and reading on this site, from guys like Iraqgunz and a few others I have been able to build 2 AR's from Scratch, finally learn that XD's arent that good of pistols and that my now favorite G21 SF is by far my fav hand gun Ive ever owned.
Ive just been trying to explain that I have 2 other AR's that do work that instead of buying something right away I can pull from them to try and fix the problem, then purchase parts as needed.
I understand and no one here would recommend you purchase anything you dont need, let alone purchase sutff you already have to begin with. That just stemmed from the guys here, including myslef, not knowing what you do or do not have on hand. -- One of the pitfalls of internet anonymity, if you will. :D
The point of the whole thing is to be methodical about it so you dont waste time and ammo. Quite fortunately in your case, you have access to different parts and ammo types on hand right away.
Swap out your BCG for another and go through the whole thing again. At this point, since it's out, you might want to go over your BCG to check for possible leaks. -- Including the gaskey bolts as MarkM pointed out in his post.
If in fact it is your BCG and you fix it and finally get it to function perfectly, go back to trying out buffers. Use the heaviest that will allow your bolt to lock back perfectly on an empty mag using your weakest ammo.
Jay Cunningham
01-25-10, 18:59
If you use 86 octane fuel in your formula one car, it probably will run crappy. If you use the correct high-octane fuel, the car will run 100%.
I am sure everybody is sick of the analogies by now, but "mil-spec" ARs are meant to run with "hot" ammo. "mil-spec" ammo is hot ammo. Many lower grade ("tier" :rolleyes:) ARs use large gas ports to help them cycle with lower pressure commercial .223 ammo.
So if your AR "cycles fine" with M855 but short strokes with UMC or Wolf... then it is sort of running the way it is supposed to. You can tweak it to run better with crap ammo, but why?
If you really want to run a lot of crap ammo I would recommend a second AR tuned more for this application.
spamsammich
01-25-10, 19:46
Guys, I have a 10.3" SBR that seems to be on the edge like jwfuhrman's. It cycles fine with full power NATO spec. 5.56, but sometimes short strokes with the lighter powered 223Rem spec. loads. I'm having a hard time understanding why some here are recommending H buffers. If a rifle is already on the edge of short stroking, won't addinig weight to the buffer decrease the stroke? I'm thinking if anything that the weight of the buffer would need to be decreased. I think my SBR has a full auto bolt carrier. So, wouldn't changing over to a lighter semiauto bolt carrier increase the stroke?
Here's a video that shows the cases ejecting while using NATO spec. 5.56 ammo.
http://www.youtube.com/watch?v=9ziYcOrzOFQ
Nice to see your flinching is more under control now, that blaster was owning you in the first video.
I for one was recommending an H because it is lighter than the buffer the OP was using and recommending that over buying a more expensive SA carrier.
Thomas M-4
01-25-10, 20:05
If you use 86 octane fuel in your formula one car, it probably will run crappy. If you use the correct high-octane fuel, the car will run 100%.
I am sure everybody is sick of the analogies by now, but "mil-spec" ARs are meant to run with "hot" ammo. "mil-spec" ammo is hot ammo. Many lower grade ("tier" :rolleyes:) ARs use large gas ports to help them cycle with lower pressure commercial .223 ammo.
So if your AR "cycles fine" with M855 but short strokes with UMC or Wolf... then it is sort of running the way it is supposed to. You can tweak it to run better with crap ammo, but why?
If you really want to run a lot of crap ammo I would recommend a second AR tuned more for this application.
+1 UMC is weak ammo when I shoot it I can feel the bolt unlocking in my LMT it feels like the BCG is moving in slow motion. It does lock the bolt back on an empty mag but the only time I have had a short stroke was using UMC ammo.
Iraqgunz makes a good point you would want your rifle to be able to work with weak ammo but some of this weak knee crap they sell has ammo is laughable.
I have found that WALLY world federal bulk pack is loaded fairly hot other than that I mostly use xm193 or q3131 the rifle was designed to shoot high pressure ammo and that is what it shoots best.
If you use 86 octane fuel in your formula one car, it probably will run crappy. If you use the correct high-octane fuel, the car will run 100%.
I am sure everybody is sick of the analogies by now, but "mil-spec" ARs are meant to run with "hot" ammo. "mil-spec" ammo is hot ammo. Many lower grade ("tier" :rolleyes:) ARs use large gas ports to help them cycle with lower pressure commercial .223 ammo.
So if your AR "cycles fine" with M855 but short strokes with UMC or Wolf... then it is sort of running the way it is supposed to. You can tweak it to run better with crap ammo, but why?
If you really want to run a lot of crap ammo I would recommend a second AR tuned more for this application.
While I understand the concept, and don't entirely disagree, and think that shooters should be sure of what they are buying and that it fits their needs and uses, I'm not sure I agree with the above as an absolute statement, especially the part I highlighted in red.
In a time when ammo costs are double what they were a couple of years ago, and loads like XM193 are not nearly as common as they once were, I would think it would be obvious why a shooter would want to be able to run "crap ammo". Not to mention the current economy where most people's priorities have shifted from spending to saving.
For me, and my purposes and uses, I want a carbine that I can run Wolf if I want/need to. If that means dropping in a lighter buffer then I'm good with that. Ideally, to me, I would like to see carbines manufactured initially to reliably run quality ammo with an H or H2 so that I can run Wolf with a C if I need to. I have owned, and come across, a few guns like this and even a few that were right on the cusp (they would shoot the Wolf fine with the C but not quite lock the bolt open on an empty magazine) and I would have preferred to have more options.
I checked and found that my 10.3" SBR has a semiauto bolt carrier, so the idea of changing from a fullauto to a semiauto bolt carrier is obviously a no go. Assuming there are no buffers that weigh less than a carbine buffer, the only thing that I can think to do is install a reduced power buffer sping. I found one on Wolf Gunspring's website. What do you think?
Robb Jensen
01-26-10, 21:33
I checked and found that my 10.3" SBR has a semiauto bolt carrier, so the idea of changing from a fullauto to a semiauto bolt carrier is obviously a no go. Assuming there are no buffers that weigh less than a carbine buffer, the only thing that I can think to do is install a reduced power buffer sping. I found one on Wolf Gunspring's website. What do you think?
You gas port should be between .071"-.073" on a 10.3" barrel and you should be using a H buffer. You should have 1x7 twist, M4 ramps and a true 5.56mm NATO chamber, my reamer always removes metal from CMMG barrels which tells me they are on the tight side.
To test for short stroking as you thing is happening you should load 10-15 known good mags with 1 round and shoot all of these. If it locks back every time it isn't short stroking.
You gas port should be between .071"-.073" on a 10.3" barrel and you should be using a H buffer.
I can't say how big the gas port hole is. Why should I be using an H buffer if the bolt carrier will only reliably lock back with full power 5.56 NATO loads (Fed XM193 and IMI M193)? It cycles fine with Prvi M193, but won't always lock the bolt carrier back. If the point of the H buffer is to add more weight to prevent the bolt carrier from going back too far, I'm not near having that problem. It seems to me if I added an H buffer, the chance of short stroking would only increase. That's why I asked about using a reduced power buffer spring.
You should have 1x7 twist, M4 ramps and a true 5.56mm NATO chamber, my reamer always removes metal from CMMG barrels which tells me they are on the tight side.
Yep, I've got all that.
To test for short stroking as you thing is happening you should load 10-15 known good mags with 1 round and shoot all of these. If it locks back every time it isn't short stroking.
I can give this a try.
There should not be any fuss getting a 10.5" barrel to run. Please contact us so we can inspect/repair if you continue to have functioning issues.
There are a few issues I have seen with lowers in regard to functioning.
Action spring weak
Wrong buffer
Burr on bolt catch causing failure to lock
Trigger group causing drag on the carrier
If you eliminate these the barrel, gas block/gas tube, or carrier key need attention.
Start with replacing the carrier with a know good one, a loose or broken carrier key screw is the most common reason I see.
I believe I have gotten it fixed, Im not 100% sure yet but I think the problem was the barrel nut was not turned(tightened) far enough, cause just a slight bend in the gas tube.
I shoots PMC 223 55gr just fine. Havnt tried anything else it.
Its a Bushmaster lower, so that could be the problem...... I want to swap out the trigger group for something better as the last time I shot it the bolt did not lock back after the last round(I threw the H2 buffer back in, along with my BCM BCG just to see if it would shoot something other than Mil-Spec ammo). The buffer may just be to heavy now and not allowing the BCG to travel all the way back.
Its freezing ass cold outside right now so I sure as shit am not going to go shoot any time soon..... this single digit weather sucks ass...... Damn Indiana..... was in the 50's this past weekend, and then dropped to less than 15 over night......
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