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Posted: 6/6/2011 7:27:49 AM EDT
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I recently installed a DD RIS II on my Colt LE6920, which requires the use of a low profile gas block. I chose a Rainier Arms unit because that's where I bought it. When I took it out to shoot on Saturday, I had a series of problems occur. The bolt only locked back on the last round once out of 4 full magazines (this was with handloads from my dad), and it had 1 fail to feed. The 3 magazines that failed to lock the bolt on the last round were each filled with Golden Tiger, PMC, and XM193.
Unfortunately, I had my girlfriend's family all there wanting some trigger time and it was getting dark so I couldn't really diagnose what was going on. A few more details: This was the first time I shot this gun. A sad combination of full time school, full time work, weather, and full time hippies shutting down all our local shooting areas led to me having it for 6 months before I could pout rounds through it. All magazines were tried and true PMags. When I got home, I was pretty worried about the gun and immediately went about cleaning it to find what the cause could be. I noticed what looked like some gas residue coming out from in front (muzzle side) of the gas block and also around the gas tube itself where it inserts into the gas block was pretty dirty. I'm guessing that too much pressure is escaping out from under the gas block, which leads to the bolt carrier not getting enough pressure through the key to properly function. Thoughts? I'll drive down to Rainier Arms if the gas block seems to be the culprit and see what they have to say. |
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Quoted:
I recently installed a DD RIS II on my Colt LE6920, which requires the use of a low profile gas block. I chose a Rainier Arms unit because that's where I bought it. When I took it out to shoot on Saturday, I had a series of problems occur. The bolt only locked back on the last round once out of 4 full magazines (this was with handloads from my dad), and it had 1 fail to feed. The 3 magazines that failed to lock the bolt on the last round were each filled with Golden Tiger, PMC, and XM193. All magazines were tried and true PMags. When I got home, I was pretty worried about the gun and immediately went about cleaning it to find what the cause could be. I noticed what looked like some gas residue coming out from in front (muzzle side) of the gas block and also around the gas tube itself where it inserts into the gas block was pretty dirty. I'm guessing that too much pressure is escaping out from under the gas block, which leads to the bolt carrier not getting enough pressure through the key to properly function. What stock/buffer setup? Did you install the gas block? If yes, how did you align it with the gas hole in the barrel? It's normal to have some gas blow by around a new build. Carbon build up will eventually seal this gap. Did it work correctly with the same ammo and magazines before the swap? Do the magazines lock the bolt back when cycling by hand? |
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Quoted:
Quoted:
I recently installed a DD RIS II on my Colt LE6920, which requires the use of a low profile gas block. I chose a Rainier Arms unit because that's where I bought it. When I took it out to shoot on Saturday, I had a series of problems occur. The bolt only locked back on the last round once out of 4 full magazines (this was with handloads from my dad), and it had 1 fail to feed. The 3 magazines that failed to lock the bolt on the last round were each filled with Golden Tiger, PMC, and XM193. All magazines were tried and true PMags. When I got home, I was pretty worried about the gun and immediately went about cleaning it to find what the cause could be. I noticed what looked like some gas residue coming out from in front (muzzle side) of the gas block and also around the gas tube itself where it inserts into the gas block was pretty dirty. I'm guessing that too much pressure is escaping out from under the gas block, which leads to the bolt carrier not getting enough pressure through the key to properly function. What stock/buffer setup? Did you install the gas block? If yes, how did you align it with the gas hole in the barrel? It's normal to have some gas blow by around a new build. Carbon build up will eventually seal this gap. Did it work correctly with the same ammo and magazines before the swap? Do the magazines lock the bolt back when cycling by hand? It's the standard Colt buffer tube with H buffer. Yes, I installed it. I drew a line straight back from the gas hole with a sharpie and then centered the gas block with that line. Like I said, this is the first time I have shot the gun. The same ammo and mags work wonders in my other Colt and in my Franken-gun. Everything works fine when cycling by hand. I actually just read Rainier Arms product description of this gas black and it leads me to believe the gas block is the culprit. Quoted from their site: "Rainier Arms Low Profile Match Grade Gas Block was designed to fit the match grade barrels in the market place. Many of the LP gas blocks in the marketplace to day are designed to fit service grade barrels. If you have ever tried to install a VLTOR or Stag style gas block on a Match Grade Stainless Steel barrel, you know that many times, the gas blocks are just too tight and will either seriously mar the barrel or sometimes, you have to ream out the gas block to a larger inner diameter. Our new LP MatchGrade block was purposely made .005 larger to fit better on match grade barrels." It seems as if a service grade barrel is not the right piece for that gas block to straddle. |
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You might want to use a dimple jig to align the hole in the barrel with the hole in the block. I've noticed that some of mine are set off the metal contact point (increased diameter) by a good distance. This also aligns thing to avoid rotational offset. If the hole isn't aligned you will get more gas blowby from around the block. You may just want to send it in and have it installed professionally and perhaps pinned on.
The jig is aligned with a tapered pin threaded into the gas hole and one threaded pin to hold in place, then the dimples are drilled under the barrel. Or look HERE 
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if the block is pinned on, I could see a issue with the .005 oversize. If its using the set screws, when they are tight, it will "pull" the gas block material around the barrel.
I have the same part, and I snugged the set screws, into there dimples, THEN removed only one, covering the threads with blue lock tite, and a single drop into the hoie for the set screw. Tighted it up and then removed the other, and lock tite. Mines sealed 100% and has never leaked Keep in mind that the gas block isnt ment to be up to the sholder on the barrel. There is a sheetmetal part you probibly arnt using to full the gap...BUT when I measured mine out, the GB hole is larger then the barrel, so some missalignment isnt a issue. |
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Quoted:
You might want to use a dimple jig to align the hole in the barrel with the hole in the block. I've noticed that some of mine are set off the metal contact point (increased diameter) by a good distance. This also aligns thing to avoid rotational offset. If the hole isn't aligned you will get more gas blowby from around the block. You may just want to send it in and have it installed professionally and perhaps pinned on. The jig is aligned with a tapered pin threaded into the gas hole and one threaded pin to hold in place, then the dimples are drilled under the barrel. Or look HERE http://i90.photobucket.com/albums/k261/dynemd/Dimple.jpg http://i90.photobucket.com/albums/k261/dynemd/Dimple1.png http://i90.photobucket.com/albums/k261/dynemd/Dimple2.png I love this tool, I use it on all my LP gas block installs (5 so far). |
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If the weapon worked prior to you installing the gas block You installed it wrong That's the question... I assume it would have worked prior to installing the new rail and gas block. I'm in my junior year of electrical engineering and although I bought the rifle in January, every potential shooting date I planned was either rained out or had to cancel to work on school. It's been a hard year. But this summer will be a summer of flying lead for me. And no, it's not dimpled 
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You removed a standard front site tower to install the gas block? Cut it down to low pro size, reinstall and problem solved. I have a self admitted Koolaid problem... I don't like permanently modifying Colt parts. I'm sure someone will have something to say about that but oh well suckers. I contacted Rainier Arms about it, John was very helpful. His suggestion was to shoot it and see if it sealed up, but to let him know if that doesn't work and we'd move to the next step. Guess that means I have to take a few hundred rounds out this weekend 
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did you set the gas block off the shoulder ? (allowing for the width of the handguard cap that is no longer there?)
only thing i can think of that would make a difference. I would uninstall it check everything then reinstall it double checking things and try again. |
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