hi guys hope someone can help i built a sog lower all mill spec stuff then i bought an rguns 20'' upper bull barrel using good brass ammo it shoots great but won't feed the next shell i put 40 rounds threw it tried 4 different mags still no luck tried my lower on another upper and it works great can anyone help me out with info thanks wayne
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ar problems
- Thread starter wayno12
- Start date
xtry51
NES Member
Short stroking. One of following:
Buffer too heavy.
Gas block not lined up with hole in barrel.
Hole in barrel too small or too big.
No gas rings on bolt.
Key on BCG not staked properly and now loose.
Buffer too heavy.
Gas block not lined up with hole in barrel.
Hole in barrel too small or too big.
No gas rings on bolt.
Key on BCG not staked properly and now loose.
usp45ct
NES Member
Kind of a stupid one but what stock do you have on it? If you have something like a Magpul PRS and you use an A2 screw, this would stop the bolt from going all the way back. Normally, the bolt would not lock to the rear, in extreme cases it would not cycle.
The he bright side is a $2.46 fix. Ask me how I know....
The he bright side is a $2.46 fix. Ask me how I know....
Golddiggie
NES Member
Try the BCG from the upper that functions in the one that doesn't function properly. Try the issue upper on a different lower too. What length gas system/tube is on the 20" upper and the upper that worked with that lower? Weight of the buffer in the tube on the lower?
I would agree with everything said above. Is it properly ejecting the spent casing, and then failing to pick up the next? Or are you not even getting ejection every time? Does the BCG ever get stuck and you have to mortar the rifle to get it back?
I would guess this is something xtry57 said. Most likely gas hole not correct size, or gas block isn't lined up properly, or similar. But a few more things to check just in case...
- Alignment of gas tube in upper. Pull the BCG back and inspect inside the channel. See if it looks bent/crooked, etc. Any excessive wear on gas tube indicating it is scraping inside the gas key?
- Gas tube out of spec or upper out of alignment. Remove the bolt from the BCG. With your hand, slide the carrier in and out of battery and feel for any excessive friction or catching as the gas tube enters the gas key. It should be really smooth and unnoticeable.
- Did you use some aftermarket fancy buffer spring?
I've dealt with a bunch of AR-15's that short stroke now so I've seen a bunch of these problems happen. One rifle the gas tube was out of spec and as the hot gas went through the end of the tube would expand enough to jam up in the gas key. Figured that out with the second bullet I mentioned, as you ran the carrier through, you'd feel it get tight on the tube. Another one, I tried everything and replaced just about every part with a known working part, and it ended up being an under spec gas hole in the barrel. A third one, my buddy used one of those Wolff extra power springs and it was too stiff for the rifle length gas system and BCG he was running and all it needed was a regular old cheap buffer spring.
If you have known working parts, that is the easiest way to quickly diagnose it. Swap parts until you figure out the bad one.
Lucky for you, you bought the upper assembled so you could just let Rguns deal with it. If it wasn't Rguns, I would say just return it, but since it might be 6 months before you get it back, maybe a little testing on your own would be worth it.
I would guess this is something xtry57 said. Most likely gas hole not correct size, or gas block isn't lined up properly, or similar. But a few more things to check just in case...
- Alignment of gas tube in upper. Pull the BCG back and inspect inside the channel. See if it looks bent/crooked, etc. Any excessive wear on gas tube indicating it is scraping inside the gas key?
- Gas tube out of spec or upper out of alignment. Remove the bolt from the BCG. With your hand, slide the carrier in and out of battery and feel for any excessive friction or catching as the gas tube enters the gas key. It should be really smooth and unnoticeable.
- Did you use some aftermarket fancy buffer spring?
I've dealt with a bunch of AR-15's that short stroke now so I've seen a bunch of these problems happen. One rifle the gas tube was out of spec and as the hot gas went through the end of the tube would expand enough to jam up in the gas key. Figured that out with the second bullet I mentioned, as you ran the carrier through, you'd feel it get tight on the tube. Another one, I tried everything and replaced just about every part with a known working part, and it ended up being an under spec gas hole in the barrel. A third one, my buddy used one of those Wolff extra power springs and it was too stiff for the rifle length gas system and BCG he was running and all it needed was a regular old cheap buffer spring.
If you have known working parts, that is the easiest way to quickly diagnose it. Swap parts until you figure out the bad one.
Lucky for you, you bought the upper assembled so you could just let Rguns deal with it. If it wasn't Rguns, I would say just return it, but since it might be 6 months before you get it back, maybe a little testing on your own would be worth it.
Some good advice thus far.
First: Start with a standard buffer, your other upper might run on a different weight depending on its configuration.
Next: call the manufacturer. We all enjoy a good troubleshoot thread but if you bought this upper complete and it's not working out of the box they need to hear about it. They'll also know the common problems and solutions for their builds.
Third: field strip and clean completely. Leave it a little wet with CLP. You should do this with any new gun since the maker will often lightly coat them fine coating of god-knows-what to prevent corrosion. Guns/parts can sit for years unused.
Fourth: while you have it apart check the gas system for leaks: plug the chamber with a finger, blow down the barrel, then put your finger over the gas tube--is there pressure? Check the BCG and key too. Is the key fastened to the BCG tight and air tight? You can try blowing into that too. If you think there might be leaks, put soapy water around the suspected areas and look for bubbles.
First: Start with a standard buffer, your other upper might run on a different weight depending on its configuration.
Next: call the manufacturer. We all enjoy a good troubleshoot thread but if you bought this upper complete and it's not working out of the box they need to hear about it. They'll also know the common problems and solutions for their builds.
Third: field strip and clean completely. Leave it a little wet with CLP. You should do this with any new gun since the maker will often lightly coat them fine coating of god-knows-what to prevent corrosion. Guns/parts can sit for years unused.
Fourth: while you have it apart check the gas system for leaks: plug the chamber with a finger, blow down the barrel, then put your finger over the gas tube--is there pressure? Check the BCG and key too. Is the key fastened to the BCG tight and air tight? You can try blowing into that too. If you think there might be leaks, put soapy water around the suspected areas and look for bubbles.
1903Collector
NES Member
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Last edited:
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