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Posted: 3/21/2016 7:58:29 AM EDT
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I bought a DIY kit from Ground Zero Precision, which included a 10" KEYMOD floating handguard. This appears to be a PRESMA Gorilla series hand guard, but GZP kits don't have suppliers names on anything.
The issue is when I tighten up the 4x set screws that attach the guard to the barrel nut, the front of the guard pulls down towards the barrel, and it doesn't matter what kind of sequence I tighten the screws. When I put my straight edge across the length of the hand guard and the upper reciever (all picatinny) the end closest to the barrel will drop down as much a 3/16". I ran 250 rounds through the rifle, got it nice and warm, even tried re-torquing the barrel nut, but it seems the set screws and the grooves in the barrel nut are still slightly mis-aligned. The reason this is such an issue is that I run out of adjustment on my front sight and am still hitting half a target too high at 25 yards. My curiosity is if anyone else has experienced this sort of issue, and what is the best (not easiest) way to permanently fix this issue? (And of course, GZP is yet to return my calls, emails, etc...) -Bobby |
| Try installing with the top rail and upper upside down on a very flat surface. I've needed to install some rails on my kitchen granite countertop. One rail in particular is always a pain and I hate having to take it off, since it needs to be installed on the countertop and each screw turned a teeny bit at a time to get it to eventually tighten down straight. It can be slow and a bit of trial and error at times. If you think the rail holes are not aligned properly than there's a problem and maybe it needs to be swapped. ALG EMR is the only FF rail I've done that went on straight without any issue. A 3rd FF rail I have actually came with the rail holes egged out slightly to allow for some adjustment due to manufacturing tolerances and error. Once the screws are tightened down the rail doesn't budge though. |
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Quoted:
Try installing with the top rail and upper upside down on a very flat surface. I've needed to install some rails on my kitchen granite countertop. One rail in particular is always a pain and I hate having to take it off, since it needs to be installed on the countertop and each screw turned a teeny bit at a time to get it to eventually tighten down straight. It can be slow and a bit of trial and error at times. If you think the rail holes are not aligned properly than there's a problem and maybe it needs to be swapped. ALG EMR is the only FF rail I've done that went on straight without any issue. A 3rd FF rail I have actually came with the rail holes egged out slightly to allow for some adjustment due to manufacturing tolerances and error. Once the screws are tightened down the rail doesn't budge though. Either you're using cheap fore ends or your assembly technique is lacking. Not being a jerk, but you should be getting better than 33% odds provided you're not installing made in China handguards (which are a crapshoot). OP, it's difficult to see what's going on without pictures. I went your parts kit mfg website, but couldn't see enough of the mounting system to figure out what might be going wrong. Looks like the barrel nut has 4 flats milled on it, 1 for each of the set/grub screws. So try to post pics and maybe somebody can help. |
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Either you're using cheap fore ends or your assembly technique is lacking. Not being a jerk, but you should be getting better than 33% odds provided you're not installing made in China handguards (which are a crapshoot). Its actually very common for FF rails to tighten down a little offset without help from a flat surface or carry handle / scope riser mount. My FF rails are installed perfectly straight. You may not be a jerk but your comment is pretty asinine. |
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Quoted:
Its actually very common for FF rails to tighten down a little offset without help from a flat surface or carry handle / scope riser mount. My FF rails are installed perfectly straight. You may not be a jerk but your comment is pretty asinine. Quoted:
Quoted:
Either you're using cheap fore ends or your assembly technique is lacking. Not being a jerk, but you should be getting better than 33% odds provided you're not installing made in China handguards (which are a crapshoot). Its actually very common for FF rails to tighten down a little offset without help from a flat surface or carry handle / scope riser mount. My FF rails are installed perfectly straight. You may not be a jerk but your comment is pretty asinine. You're talking about lining up two flat planes (receiver rail and foreend top rail) that are separated by less than 1/16". It isn't difficult nor does it require anything more than a pair of eyes. OP doesn't need a flat surface or a carry handle or a scope mount. He needs the grooves in his barrel nut to align correctly. He might be able to loosen and then retorque the barrel nut and get it aligned correctly OR its possible the barrel nut grooves were not machined correctly. OP, it would help if you could post pics of how far misaligned the rails are. If you're off a hair, you could back off or tap the barrel nut tighter to get it aligned correctly. |
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Quoted:
You're talking about lining up two flat planes (receiver rail and foreend top rail) that are separated by less than 1/16". It isn't difficult nor does it require anything more than a pair of eyes. OP doesn't need a flat surface or a carry handle or a scope mount. He needs the grooves in his barrel nut to align correctly. He might be able to loosen and then retorque the barrel nut and get it aligned correctly OR its possible the barrel nut grooves were not machined correctly. OP, it would help if you could post pics of how far misaligned the rails are. If you're off a hair, you could back off or tap the barrel nut tighter to get it aligned correctly. Quoted:
Quoted:
Quoted:
Either you're using cheap fore ends or your assembly technique is lacking. Not being a jerk, but you should be getting better than 33% odds provided you're not installing made in China handguards (which are a crapshoot). Its actually very common for FF rails to tighten down a little offset without help from a flat surface or carry handle / scope riser mount. My FF rails are installed perfectly straight. You may not be a jerk but your comment is pretty asinine. You're talking about lining up two flat planes (receiver rail and foreend top rail) that are separated by less than 1/16". It isn't difficult nor does it require anything more than a pair of eyes. OP doesn't need a flat surface or a carry handle or a scope mount. He needs the grooves in his barrel nut to align correctly. He might be able to loosen and then retorque the barrel nut and get it aligned correctly OR its possible the barrel nut grooves were not machined correctly. OP, it would help if you could post pics of how far misaligned the rails are. If you're off a hair, you could back off or tap the barrel nut tighter to get it aligned correctly. I honestly don't think it matters as long as it's consistent. |
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I don't have pictures *yet* but should have taken them before I put the guard back on this last time. I could see that the set screws were making some indentions just off of center toward the reciever side of the barrel nut grooves. They definitely aren't hitting the centers. By the measurements I am able to take with just a dial caliper, everything looks to be pretty square. It would seem to me that the barrel nut is the realistic culprit, in that the grooves don't line up exactly with the set screw holes in the hand guard.
There are 4 flat sides on the barrel nut, and there are 2x half-round grooves that run the OD of the nut; these 2x grooves are where the set screws reside. I do not believe the upper face is perfectly flat, because even if I try to shim the bottom between the guard and the receiver, it literally just pushes farther away leaving a bigger gap *and* still does the nose dive at the front. I don't have a carry handle on this one, just a railed upper and hand guard. As a temporary (until I can get one of machine shop buddies to take a gander), I found that when the hand guard is perfectly level and straight with the upper receiver, the gap between the guard and the gas block is 0.15". So, I fabricated me a shim and have it sitting on the gas block. When I tighten the set screws, the end of the guard doesn't nose dive. I see a potential issue with this though, which is it's putting just a wee bit of push down on the barrel, which does have a little bit of flex in it. So i'm trying to balance having something to stop the nose-diving hand guard and not flexing the barrel either. If I crank down on the set screws, i can tell the barrel is getting a little bit of a bind, so I've got some red loc-tite on the screws and have them just tight enough so that the guard doesn't have any movement; hopefully enough to get my iron sight zeroed. |
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Quoted:
I don't have pictures *yet* but should have taken them before I put the guard back on this last time. I could see that the set screws were making some indentions just off of center toward the reciever side of the barrel nut grooves. They definitely aren't hitting the centers. By the measurements I am able to take with just a dial caliper, everything looks to be pretty square. It would seem to me that the barrel nut is the realistic culprit, in that the grooves don't line up exactly with the set screw holes in the hand guard. There are 4 flat sides on the barrel nut, and there are 2x half-round grooves that run the OD of the nut; these 2x grooves are where the set screws reside. I do not believe the upper face is perfectly flat, because even if I try to shim the bottom between the guard and the receiver, it literally just pushes farther away leaving a bigger gap *and* still does the nose dive at the front. I don't have a carry handle on this one, just a railed upper and hand guard. As a temporary (until I can get one of machine shop buddies to take a gander), I found that when the hand guard is perfectly level and straight with the upper receiver, the gap between the guard and the gas block is 0.15". So, I fabricated me a shim and have it sitting on the gas block. When I tighten the set screws, the end of the guard doesn't nose dive. I see a potential issue with this though, which is it's putting just a wee bit of push down on the barrel, which does have a little bit of flex in it. So i'm trying to balance having something to stop the nose-diving hand guard and not flexing the barrel either. If I crank down on the set screws, i can tell the barrel is getting a little bit of a bind, so I've got some red loc-tite on the screws and have them just tight enough so that the guard doesn't have any movement; hopefully enough to get my iron sight zeroed. I understand the groove thing, i looked up your handguard and have a similar setup on my match rifles. if you're shimming the barrel against the gas block, a few notes to point out: 1) the barrel is interacting with the handguard now, which isn't really an effective free-flotaing handguard 2) unless it's a really thick shim, that's a lot of flex. Measure the grooves from the rear of the barrel nut and compare up, down, left, and right. The distances should be the same. Marking the nut with a paint pen might help, the sides look the same. if you have a square, hit that upper receiver real quick just to make sure that it is, you know... square. Comparing the top of the handguard to the top of the receiver (especially visually) doesn't really tell you anything. The handguard is simply going where the receiver is telling it to with the pressure you're applying. you need to make sure the receiver is squared. After you find that the receiver is in fact square, you need to find a new handguard that doesn't have poor manufacturing tolerances. I'm not trying to rub salt in anything, really. I'm trying to help. But brother, there's a reason those kits are so cheap. |
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