2 weeks ago I got my tax stamp for my SBR. I took my 10.5 inch barrel and my AR to my local gun guy and had him install the new barrel. My first trip to the range was BAD, it jammed about every 3 rounds, the empty brass would not eject and ride over the new round trying to go into the chamber. I took it back to the shop and we discovered that the gas block would not line up properly with the gas port because it was slightly out of spec. We replaced it with a Noveske gas block and I headed back to the range. It did better but would only get through about 5 rounds before jamming up again 
Back at the shop we concluded that the gas port was not large enough, so we opened the gas port to .092 (it was 0.80), I took it back to the range and it did good. It ate the first 30 rounds no problem, jammed 2-3 times on the second mag, them fired a third mag no problem. I thought the problem was fixed…
Well I took it out today and with in the first 15 rounds it jammed 3 times. I took it back to the shop and we decided to make sure it wasn’t a bolt problem so we replaced everything on the bolt and bolt carrier (extractor, springs, ect) and took it back to the range. It shot 55 rounds without a problem and then the jams came again. On the last round the bolt actually locked back with an empty brass sitting on top of the mag.
While shooting I noticed that the brass would only eject about 4 or 5 feet vs. 10-15 feet they would fly before I installed the short barrel. Everything on the gun is original (buffer, buffer spring, bolt carrier, ect)
Now my rifle is back shop, I know what its not,
ammo (I shot several different kinds)
mags (I used 4 dif mags, that all ran fine before)
cleaning or lube (the gun was cleaned and lubed before each range trip)
Any ideas what the problem could be?
I am going to be very blunt here. Neither of you knew what you were doing and should have left the port alone. .080 is about right for a 10.5" barrel. .092 is almost the port size for a 20" rifle system.
You also left out important information such as the make of the barrel, the type of buffer and ammunition.
Good lord, did I miss the part where you tried the different weight buffers?
Tell me you didn’t drill the gas port before considering that as the problem.
Always modify the cheapest part (buffer).
ammo was S&B, Federal, and Remington. The barrel is Rock River, we called Rock River and the rep said the only thing he could think of was that there was something wrong with the bolt carrier. The gas port size of .080 seemed fine to me as well but my local guy as well as another gunsmith from another shop (who does a lot of SBR’s) both agreed that it needed to be expanded.
Since you already replaced the extractor, next is the buffer and spring. And maybe someone with more experience can say but could your chamber be out of spec aka too tight and not let it extract freely? Do specify the ammo used as well.
My bad looked right over the ammo.
Well I hate to say this, but they are wrong. Rock River barrels are not known for their quality. Since you said that everything was working with the previous set up (unless I misread) and you then added a barrel that should be an indication.
At this point I would do the following.
Get at least an H2 buffer and blue Springco spring. Then I would use ammo that is known to work. The S&B ammo is often time REALLY hot and I had issues with it blowing primers in several of my AR’s.
I would use M855/M193 or similar as benchmark. The Remington ammo is some of the weakest I have seen.
Lube the weapon GENEROUSLY and then shoot it.
I suspect this as well.
How about the extractor spring?
Shorties are harder on extractors and usually need more spring tension than rifles.
Use a Colt Gold, BCM extra power or Rifle spring with o-ring, in that order of preference.
For the same reason, they like heavier H2 buffers.
I would also look around for a shop that actually knows ARs.
after trying the buffers and springs, A Crane O-Ring on the extractor may help too considering you had the empty brass just laying on top of the mag when the bolt locked back.
Also as one mentioned the barrel seems to be the problem
Clint, you beat me to it. I guess I had that window open without refreshing before hitting reply!
^
|
THIS
When I worked in Sillouette Arms New Hyde Park NY,
Al Pfitzmayer’s place… him former UDT Korea vintage, would have broke my balls permanently if I worked the more expensive part…
Does your smith know how to properly install a gb? Make sure there is a small gap between the back of the gb and the barrel sleeve. Imagine there was a handguard cap in the gap. Any gas leaks at the block? Doesn’t sound like any are pinned.
This could always be possible, but not likely. If you look at the size of the hole on the GB or the FSB you will see that it is several times larger than the port itself.
My guess is that was done for a reason for the exact same reason we are discussing.
What comes to mind right away is the RRA barrel and the fact that we still have no idea what kind of buffer the OP has in his gun.
The way he describes his problem, it sounds like it could be failure to extract because of a tight chamber (not uncommon on those budget barrels like RRA) or short-stroking due to his selection of the wrong buffer or spring.
If it were me, I’d get the chamber spec’d/reamed. Then I’d want to buy a couple of extra buffers in different weights and go the range to see how much I’ve screwed myself by letting an inexperienced gunsmith drill a bigger gas port in my 10.5 inch barrel.
This is the reason short barrels were considered unreliable not that long ago. No mention of extra extractor tension, or heavier buffer, then just drilling the gas port oversize.
You should replace the barrel if this is serious use carbine. Try an H3 buffer if it’s not.
You also need an extractor o-ring or extra power extractor spring with an SBR, that was the root cause of your problems.
I think we found the problem. My gunsmith took it out today and tried every buffer he had as well as a different buffer spring and a vast array of different ammo. The problem is the barrel, the chamber is sightly too long. We will be contacting Rock River on monday and try to get a refund. Regardless of what they say I will be putting a Noveske barrel on the gun.
I appreciate the feed back from everyone here.
Save yourself a headache and some cash and get a BCM 11.5" BFH barrel.
Hopefully they will do something since you may have voided any kind if warranty by opening the gas port.
Threads like this one are why I bought a 6933.
ARs just aren’t quite LEGOS yet.