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Posted: 3/12/2014 11:56:53 AM EDT
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Hey guys, my brother just finished his first upper build and I noticed that his gas block is pretty far off center. I know that the gas block holes are generally larger than the barrel's gas port, but this still seems like it might cause a problem. We won't be able to shoot it until this weekend and I'm not sure if I'll have the time to fix it before this weekend so we might just wing it when we go to shoot. The biggest problem I'm worried about though with this situation is that he dimpled the barrel for the set screws...so my guess is the dimples are pretty far off center too, which I assume means we might have to ditch the set screw type block and go for a clamp on style or a set screw type with the screws in different positions. Any suggestions guys or do any of you guys have gas blocks this far off TDC with no problems? Oh and if anyone cares the rail is the Fortis Rev 9" which is pretty nice. Thanks guys!
http://<ahttp://i1343.photobucket.com/albums/o800/jsgexplorer/gasblock2_zpsf72f9ce8.jpeg</a>" /> http://<ahttp://i1343.photobucket.com/albums/o800/jsgexplorer/54886b22-9d6d-4b8b-a1d3-923d54f27561_zpsca1e1f13.jpg</a>" /> http://<ahttp://i1343.photobucket.com/albums/o800/jsgexplorer/gasblock3_zps9074b12b.jpeg</a>" /> |
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I have seen worse, and gas tube will likely inhibit the cycling functionality, and you may be undergassed being off center that far.
I got this from a gunsmith and 200+ rifles later has yet to fail me. Here is what you need to do: Separate the upper from lower. Remove the handguard. Remove the BCG and disassemble it. Loosen the gasblock so it can rotate. With your finger in the rear of the Bolt carrier, slide it into the upper receiver. Slide the BCG as you rotate the gasblock till you have no friction from the gas tube/ carrier key interaction. Lightly tighten the gas block. Partially reinstall the handguard and notice the location of the gasblock. If close to centered, tighten the set screws in the gasblock the rest of the way using "red" loctite. Reinstall the handguard. Cheers |
This needs to be fixed before firing. Even cycling with the charging handing could cause damage. Even though the gas block does appear to be slightly off what this also causes is the gas tube to not be centered properly in the upper. By the looks of things it looks like there may be some serious binding/dragging of the gas key as it contacts the gas tube. If it's off too far you risk damaging the gas key. Even though the gas tube end that goes inside the upper is belled and the gas key is slightly flared to help guide a slightly off centered gas tube if it's off too far this could happen.
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Quoted:
I have seen worse, and gas tube will likely inhibit the cycling functionality, and you may be undergassed being off center that far. I got this from a gunsmith and 200+ rifles later has yet to fail me. Here is what you need to do: Separate the upper from lower. Remove the handguard. Remove the BCG and disassemble it. Loosen the gasblock so it can rotate. With your finger in the rear of the Bolt carrier, slide it into the upper receiver. Slide the BCG as you rotate the gasblock till you have no friction from the gas tube/ carrier key interaction. Lightly tighten the gas block. Partially reinstall the handguard and notice the location of the gasblock. If close to centered, tighten the set screws in the gasblock the rest of the way using "red" loctite. Reinstall the handguard. Cheers Damn this is brilliant! I'm gonna keep this if you don't mind. To op, fix that before you shoot it. A little off visually isn't always a problem, but that goes way beyond little. Get that gas block centered and drill a proper dimple. Hopefully the dimples he made were shallow since the new one will likely be touching it and will need to be deeper to center the screw. Or a clamp on will work too. Good luck |
| Hey guys thanks for all the tips and suggestions so far. I'm still at work so unfortunately I won't be able to do anything yet but from what I recall when I had a couple minutes to look at his gun, when I looked in the upper from the rear of the rifle (with BCG out) the gas tube was floating freely in the gas tube hole in the front of the receiver (like it wasn't touching the upper receiver - which I recall is how it should be like on the .300 Blackout upper I built myself last year). Also as far as I could tell, I didn't feel any resistance when charging the rifle, but then again I didn't have time to strip the BCG and do the test where you let the Bolt carrier slide into the upper to determine amount of resistance. But I'll try to update you guys when I can. |
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Hey guys, back with an update on this off center gas block for my brother's gun. After all your suggestions I took the rail off and tried to drill new dimples, which only slightly remedied the situation. The gas key was still binding slightly on the ejection port side of the gas tube but less than before and the gas block looked more centered than before. I slapped the thing back together and shot it a little while later, put maybe 100-150 rds through it with no problem. Shortly after that, we decided to ship the upper out with my retro XM177E2 build to John Thomas since we needed the muzzle brake pinned on and the barrel chopped on this upper. For those of you who don't go over to the retro forum or know who John Thomas (JT) is, I hafta say he is a great person to send work to and has plenty of helpful information all over ARFCOM as a member. First off his prices are unbeatable, the quality of work he does is excellent, he's very professional and helpful, he's a really nice guy to talk to, and he turned the project around in no time. I think it was about 4-5 business days door-to-door, with updates on the projects all along. Anyways some pics:
Here's the now centered gas block after JT filled in the botched dimples and redrilled proper dimples, and he even touched up the front of the gas block where my brother was beating the gas block to death when he had trouble getting it on the barrel (as you can see from the original pics up top). http://i1343.photobucket.com/albums/o800/jsgexplorer/3922b523-f1f0-4921-98c2-4d133698ab75_zps45e1fe43.jpg Here's the finished product: http://i1343.photobucket.com/albums/o800/jsgexplorer/photo_3noserial_zpseafbe9b7.jpg http://i1343.photobucket.com/albums/o800/jsgexplorer/photo_4noserial_zpsee6200d5.jpg http://i1343.photobucket.com/albums/o800/jsgexplorer/photo_15_zps7b08ac0e.jpg |
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Quoted:
Hey guys, back with an update on this off center gas block for my brother's gun. After all your suggestions I took the rail off and tried to drill new dimples, which only slightly remedied the situation. The gas key was still binding slightly on the ejection port side of the gas tube but less than before and the gas block looked more centered than before. I slapped the thing back together and shot it a little while later, put maybe 100-150 rds through it with no problem. Shortly after that, we decided to ship the upper out with my retro XM177E2 build to John Thomas since we needed the muzzle brake pinned on and the barrel chopped on this upper. For those of you who don't go over to the retro forum or know who John Thomas (JT) is, I hafta say he is a great person to send work to and has plenty of helpful information all over ARFCOM as a member. First off his prices are unbeatable, the quality of work he does is excellent, he's very professional and helpful, he's a really nice guy to talk to, and he turned the project around in no time. I think it was about 4-5 business days door-to-door, with updates on the projects all along. Anyways some pics: Here's the now centered gas block after JT filled in the botched dimples and redrilled proper dimples, and he even touched up the front of the gas block where my brother was beating the gas block to death when he had trouble getting it on the barrel (as you can see from the original pics up top). <a href="http://s1343.photobucket.com/user/jsgexplorer/media/3922b523-f1f0-4921-98c2-4d133698ab75_zps45e1fe43.jpg.html" target="_blank">http://i1343.photobucket.com/albums/o800/jsgexplorer/3922b523-f1f0-4921-98c2-4d133698ab75_zps45e1fe43.jpg</a> Here's the finished product: <a href="http://s1343.photobucket.com/user/jsgexplorer/media/photo_3noserial_zpseafbe9b7.jpg.html" target="_blank">http://i1343.photobucket.com/albums/o800/jsgexplorer/photo_3noserial_zpseafbe9b7.jpg</a> <a href="http://s1343.photobucket.com/user/jsgexplorer/media/photo_4noserial_zpsee6200d5.jpg.html" target="_blank">http://i1343.photobucket.com/albums/o800/jsgexplorer/photo_4noserial_zpsee6200d5.jpg</a> <a href="http://s1343.photobucket.com/user/jsgexplorer/media/photo_15_zps7b08ac0e.jpg.html" target="_blank">http://i1343.photobucket.com/albums/o800/jsgexplorer/photo_15_zps7b08ac0e.jpg</a> Thanks for the update report. I will say from the top pic it looks like the barrel is not centered on the hand guard. Could just be the angle the pic was taken though. Can you take a similar pic from "straight on" from the barrel end looking back toward the hand guard? |
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Thanks for the update report. I will say from the top pic it looks like the barrel is not centered on the hand guard. Could just be the angle the pic was taken though. Can you take a similar pic from "straight on" from the barrel end looking back toward the hand guard? Hey sorry yea I just took a quick pic before, here's a better one, (the camera is still a bit off center - it was a PITA to try to line it up and have the light shining through the window to light everything up lol) http://i1343.photobucket.com/albums/o800/jsgexplorer/gasblock6_zps49399331.jpg |
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You necessarily don't NEED to dimple your barrel for the gas block... Just dab some Rocksette or red Locktite on the set screws and tighten and let the glue cure.
I've used several set-screw gas blocks and put several thousand rounds though each and it's still sitting in the same spot as when I installed it. One of the Mk12s in my company didn't have dimples in the barrel for the gas block (thats the only one I saw that the armorer took apart for a re-barrel). |
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Good deal now don't let your brother near anymore rifles!  For real. He couldn't tell that the gas block was off by 8-10 degrees before he marked the spots for the dimples??? I'm glad you were there to help him. It just takes patience to do one correctly. I don't have the dimples on my Recce rifle. It has more rounds than I can count now thru it without any movement of the block or the screws. I marked the set screws (3), with a paint pin and I can see thru the rail holes that they have never moved. In my experience the dimples are nice but not an absolute necessity. Just tighten them to the upper end of the torque spec, set, mark, and forget them. Especially if the gas block is totally protected by the rail system... |
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