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Posted: 10/30/2012 8:28:38 PM EDT
If so, this is my first experience with over gassed rifles. I assembled three uppers with barrels from one manufacturer. All three are suffering short-stroking problems where the bolt will only cycle enough to eject a spent casing but not enough to strip the next round. My immediate thoughts were "gas problem" and "under gassed." The only part each upper have in common with one another are the barrels. Two 18" and one 16" lightweight, all mid-length gas. Multiple mags were tested and multiple brands of ammo as well, no dice. Mounted the uppers on several different lowers, same problems for all. I pulled apart two of the uppers and found nothing out of the ordinary. Gas blocks were aligned with the barrel's gas port, very little carbon residue blown out from under the gas blocks, gas tubes lined up nicely with plenty of give inside the action and no unusual wear, carrier keys snug as a bug and staked, gas rings a-ok. The gas systems are tight. I can only assume my uppers are over gassed because I can't see how they could be under gassed. I have an adjustable block enroute to see if I can't dial back the pressure and find a sweet spot. |
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Not likely you have an over gassing problem. I think you might be spinning your wheels trying to dial your gas down with an adjustable.
Under gassed would give your problems. Yes, holes like up but are they the right size? How did you determine your holes were lined up appropriately? What stocks and buffer wt and spring are you using? Manufacturers of barrel, gas block, bcg? |
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The uppers are as follows:
Daniel Defense 18 S2W, Troy LP gas block, standard gas tube, High Standard bolt carrier, standard MP bolt, AAC non-suppressor mount compensator. Barrel was cleaned prior to use. Spent brass looks like the above, also with a noticeable indentation on the head stamp from the ejector. Standard rifle buffer and spring. Daniel Defense 18 S2W, Troy LP gas block, standard gas tube, RRA bolt group, RRA tactical comp. Barrel was cleaned prior to use. Standard carbine buffer and spring. Daniel Defense 16 lightweight mid-length, VLTOR LP 0.625" gas block, PWS DI carrier, JP Enhanced Bolt, Spike's Dynacomp. Cleaned prior to use. Standard carbine buffer and spring. All three suffer the same malfunctions. None appear to have any dragging when the actions are manually cycled, very smooth. Receivers inside show no signs of abnormal wearing. Ammunition tested includes Igman 62-gr., Wolf 55-gr., Tula 55-gr., Prvi 62-gr., PMC X-Tac 62-gr., Prvi 75-gr match and a handful of Radway Green. I also assembled three other rifles in the same period, one in .300BLK with a 16" AAC barrel, a retro 5.56 XM177E2 build with a Bushmaster superlight and a 5.56 with a Rainier Arms select barrel. No problems with any of those or the other AR's I assembled in the past. I use a jig to mark the location of the gas port on the underside of the barrel and I install set screw gas blocks to align with those marks. Upon removing the gas blocks, there is a ring of carbon from the gas block's port centered around the hole from the barrel gas port, so they are properly aligned. Standard barrel nuts are torqued to 30 ft-lbs, aligned with the receiver not exceeding 80-ft-lbs and do not impinge on the gas tubes. In early troubleshooting I replaced the gas tubes with ones known to work in other rifles. Keys are torque-tested and staked with a MOACKS tool. Gas rings were brand new when installed and are all in good condition. The bolts show normal signs of operation- they all have carbon buildup where they should and none where they shouldn't. ETA: I use Rocksett to mount the gas blocks, it took a full day of soaking before I could remove them. They were anchored in place tightly and didn't move. The rifles don't appear to be losing gas anywhere, and comparatively the gas ports look as large as they should be next to other barrels with mid length gas systems and equal overall lengths. I'll get the calipers out and check ports on an 18" and the 16" tonight if I have time. ETA: The 18 gas port measured in at 0.0725" +/- with calipers under a magnifier. Adjusted any larger and I could see barrel on either side of the port through the caliper jaws. |
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Quoted:
Not likely you have an over gassing problem. I think you might be spinning your wheels trying to dial your gas down with an adjustable. Under gassed would give your problems. Yes, holes like up but are they the right size? How did you determine your holes were lined up appropriately? What stocks and buffer wt and spring are you using? Manufacturers of barrel, gas block, bcg? Like he said, what springs and buffers are you using |
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Quoted:
Quoted:
Not likely you have an over gassing problem. I think you might be spinning your wheels trying to dial your gas down with an adjustable. Under gassed would give your problems. Yes, holes like up but are they the right size? How did you determine your holes were lined up appropriately? What stocks and buffer wt and spring are you using? Manufacturers of barrel, gas block, bcg? Like he said, what springs and buffers are you using As I posted above, standard weight buffers and standard strength springs. I weighed the rifle buffer in at 5.2 ounces. I replaced the spring with a new one. I highly doubt my problems are buffer related as each rifle uses a slightly different setup. This is really beyond me at this point. |
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I don't understand this using Rocksett to mount gas blocks. That is put between the barrel and the gas block? Clamp the thing down, taper pins, or dimple the barrel as appropriate.
Ammo - Not sure about some of that ammo, Tula for sure is under powered, Wolff is debatable, haven't had experience with the others. Get some Federal XM193 and have a go. Part of me says it's something you are doing in your builds like the Rocksett on the gas blocks. ETA - I concur your bolt looks dry. |
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Quoted:
I don't understand this using Rocksett to mount gas blocks. That is put between the barrel and the gas block? Clamp the thing down, taper pins, or dimple the barrel as appropriate. Ammo - Not sure about some of that ammo, Tula for sure is under powered, Wolff is debatable, haven't had experience with the others. Get some Federal XM193 and have a go. Part of me says it's something you are doing in your builds like the Rocksett on the gas blocks. ETA - I concur your bolt looks dry. Rocksett is applied on the set screws as a thread locker. It's the Troy gas block. I replaced it with a PRI adjustable, twisted out the gas screw about halfway to where the port is nearly half closed and the rifle was cycling strongly and reliably. Something about that Troy block is cutting my operating pressures way down if the rifle cycles with a half closed gas port. |
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I agree with 007Kevin............You aren't over gassed you are UNDER gassed. Now I do use adjustable gas blocks on my builds, but that's besides the point. I've had a one so over gassed the extractor was ripping the brass cased rim off the case. That was over gassing.
As to the rockset, not sure. But I do use Loctite bearing seal ( green ) under every gas block I've ever installed. I also put a small ring around both ends. But I do use an air hose down the barrel to make sure there is none in the gas port, or tube. I've never had a gas block show any carbon fouling around them. Maybe a little around the gas tube. But lately I've been adding a drop there too. Oh I too dimple the barrels. But just use Blue loctite there |
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I would see how the Gas Tube lines up in the Gas Block. Possibly the hole isnt going throught all the way or has a big burr. Also contact Troy and see what they say. MAHA Lines up, clear shot for the pressure into the gas tube, no burrs. The gas port in the Troy block is also larger than the PRI adjustable by far, which is strange since the rifle doesn't have enough pressure to cycle when the Troy is installed; it both has a larger port and the PRI is partially closed too. I'm going to measure the distance from the end of the block to the center of the port to see if it simply isn't lining up over the port in the barrel. I'm going to call them today if I have time. I like the PRI block, it's just to large to work with my Troy Alpha rail. |
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Quoted:
Quoted:
I would see how the Gas Tube lines up in the Gas Block. Possibly the hole isnt going throught all the way or has a big burr. Also contact Troy and see what they say. MAHA Lines up, clear shot for the pressure into the gas tube, no burrs. The gas port in the Troy block is also larger than the PRI adjustable by far, which is strange since the rifle doesn't have enough pressure to cycle when the Troy is installed; it both has a larger port and the PRI is partially closed too. I'm going to measure the distance from the end of the block to the center of the port to see if it simply isn't lining up over the port in the barrel. I'm going to call them today if I have time. I like the PRI block, it's just to large to work with my Troy Alpha rail. Try a JP Lo Pro gas block The .750 one fits under my Apex hand guard. I used to be a tool and Die Maker. I set up all of my gas blocks mathematically. I check the distance from the edge of the bigger Dia. of the barrel, to the farthest edge of the gas port, with a dial caliper, subtract 1/2 of the hole Dia. for my Centerline. On the gas block I insert the proper size drill into the port. Then use a depth mike to measure from the edge of the gas block to the edge of the drill. then add 1/2 the Dia. to that measurement. determine the distance from the shoulder to the back of the gas block. Then I use the correct amount of shims to set that distance. Slide, or tap it back tight against the shims, line it up vertically, and tighten down the set screws. once my Green Loctite has set up, I remove 1 set screw drill down that hole about .125, tap it. Put that screw back in, then I do the same to the other. Blue loctite on the screws "I'm Good To Go" Yes I do have a drill press. |
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