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Posted: 12/13/2009 6:47:37 AM EDT
| I just installed a KAC RAS on a new build and I am curious about how these match the top rail on the receiver. There is a very slight off-set (jog to the right) on the RAS, as compared to the top rail of the receiver. Is this pretty normal for these non-FF rails? The off set is not real noticeable, but if you sight down the top of the receiver, you can see it. I cannot see why it would be an issue anyway, since I am really just using the RAS as hand guards, but I wanted to get a second opinion. I think I am just used to Larue or DD free float rails that line up exact. Anyone else have a RAS that does not line up perfect with the upper receiver? |
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Thanks for the replies. The height is lined up ok. I had no problem with the rail clamp seating under the barrel nut. It is from side to side where I can see the slight jog from the upper receiver rail to the RAS rail. Yes, I believe that it is installed correctly, as I used the instructions and it snapped in without issue. I tried to remove it and slide it to the left to be sure they lined up perfectly, but the rail just re-seats in the same position and cannot be rotated.
This might sound a little goofy, but any chance the barrel nut needs to be tightened a very slight hair to bring the rail over? I had no problem with the barrel install and the gas tube was installed without any issue at all. I only ask because I am not sure how the RAS locks up to the barrel nut and if it would matter? Any ideas? |
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No, you do not need to mess with the barrel nut or any other part of the weapon to install the RAS, assuming the upper was correctly assembled.
When you installed the top half, did you make sure the front spring tab went under/inside the front handguard cap? Yeah, no problem there. I agree on the barrel nut, as I did not see how that could have any bearing on the hand guard. Like I said, my Larue and DD free float rails are exactly perfect with the upper receiver. I have a Troy drop in and it is slightly off as well. Maybe it's just how they snap in place. Quoted:
Might just take them off and reinstall them, see how it goes. I did, but I will go ahead and do it again. Maybe I can rotate it over slightly as I snap it in place. The problem is there is not any play in the hand guard cap or where the retaining latch slips down over the gas tube. Hmm... Weird! It's not like it is really noticeable, you have to really sight down the receiver to see the off set. If I can, I will take a pic and post it. Maybe I am just concerned about nothing? 
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It's the barrel nut... 
ETA: There are two pins on the rear of the RAS which engage teeth on the nut. Bingo!! The is 100% a barrel nut issue. I have installed a few hundred sets of these. One or two degrees off and you will have the RAS canted to one side or another slightly. Nothing that would cause a functioning problem but the RAS has tabs that go into the barrel nut notches as well as the clamp. Barrel nut is off ever so slightly than so are the notches and so is your RAS. Trust me. |
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Yep. The RAS does NOT clamp to the gas tube as a few people have mentioned.
It indexes off of the barrel nut. If you have the tools, and assuming the nut is off the direction that you'd be tightening it to correct it, you could honestly do it without even removing the gas tube, so long as you're careful. Just put the wrench in place and apply a little torque until the nut moves slightly. Check it with the RAS, move again if need be. |
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Yep. The RAS does NOT clamp to the gas tube as a few people have mentioned. It indexes off of the barrel nut. If you have the tools, and assuming the nut is off the direction that you'd be tightening it to correct it, you could honestly do it without even removing the gas tube, so long as you're careful. Just put the wrench in place and apply a little torque until the nut moves slightly. Check it with the RAS, move again if need be. it may not "clamp" to it, but it does clip over it. |
| Well damn... I thought maybe it had something to do with the barrel nut, due to the way it was lining up. The concern is that I am already between 70 and 75 ft. lbs. of torque now. I would be pushing the max to get it line up perfect. I could see adjusting it with the gas tube installed, but with that much torque, I should probably just pull it apart and start over. I am tempted to just leave it, as there is no concern over function, but every time I look at it, it will bug me. I will probably just go back to the very beginning and re-time the nut. What a pain in the ass! |
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Yep. The RAS does NOT clamp to the gas tube as a few people have mentioned. It indexes off of the barrel nut. If you have the tools, and assuming the nut is off the direction that you'd be tightening it to correct it, you could honestly do it without even removing the gas tube, so long as you're careful. Just put the wrench in place and apply a little torque until the nut moves slightly. Check it with the RAS, move again if need be. it may not "clamp" to it, but it does clip around over it. The clamp should not touch the gas tube |
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Yep. The RAS does NOT clamp to the gas tube as a few people have mentioned. It indexes off of the barrel nut. If you have the tools, and assuming the nut is off the direction that you'd be tightening it to correct it, you could honestly do it without even removing the gas tube, so long as you're careful. Just put the wrench in place and apply a little torque until the nut moves slightly. Check it with the RAS, move again if need be. it may not "clamp" to it, but it does clip around over it. The clamp should not touch the gas tube i'm talking about the clip on top front of the HG. |
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Yep. The RAS does NOT clamp to the gas tube as a few people have mentioned. It indexes off of the barrel nut. If you have the tools, and assuming the nut is off the direction that you'd be tightening it to correct it, you could honestly do it without even removing the gas tube, so long as you're careful. Just put the wrench in place and apply a little torque until the nut moves slightly. Check it with the RAS, move again if need be. it may not "clamp" to it, but it does clip around over it. The clamp should not touch the gas tube i'm talking about the clip on top front of the HG. On mine, the RAS did slide on top of the gas tube. In fact, there was so much pressure that I was scared it was going to crimp the gas tube. I had to clamp it on and off a spare gas tube to be sure it did not pinch the tube. ETA: I am referring to front of the hand guard as well. |
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Yep. The RAS does NOT clamp to the gas tube as a few people have mentioned. It indexes off of the barrel nut. If you have the tools, and assuming the nut is off the direction that you'd be tightening it to correct it, you could honestly do it without even removing the gas tube, so long as you're careful. Just put the wrench in place and apply a little torque until the nut moves slightly. Check it with the RAS, move again if need be. it may not "clamp" to it, but it does clip around over it. The clamp should not touch the gas tube i'm talking about the clip on top front of the HG. Gotcha. My post was referring to where the clamp on the RAS is, near the barrel nut. |
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Yep. The RAS does NOT clamp to the gas tube as a few people have mentioned. It indexes off of the barrel nut. If you have the tools, and assuming the nut is off the direction that you'd be tightening it to correct it, you could honestly do it without even removing the gas tube, so long as you're careful. Just put the wrench in place and apply a little torque until the nut moves slightly. Check it with the RAS, move again if need be. it may not "clamp" to it, but it does clip around over it. The clamp should not touch the gas tube i'm talking about the clip on top front of the HG. Gotcha. My post was referring to where the clamp on the RAS is, near the barrel nut. oh, yeah, the front tab should be under the Handguard tab, and it should be some pressure, then the Rear clamp around the gas tube. |
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Well damn... I thought maybe it had something to do with the barrel nut, due to the way it was lining up. The concern is that I am already between 70 and 75 ft. lbs. of torque now. I would be pushing the max to get it line up perfect. I could see adjusting it with the gas tube installed, but with that much torque, I should probably just pull it apart and start over. I am tempted to just leave it, as there is no concern over function, but every time I look at it, it will bug me. I will probably just go back to the very beginning and re-time the nut. What a pain in the ass! If it makes you feel any better back in 2002 we received about 2000 RAS to install on our M4s which were plain Jane slicks at the time. I did about a third of them and over half needed to have the barrel nut re-torqued. We could have just left them but the powers that be (one O4 in particular) would never have let it go. You are best off loosening and re-torquing the nut. You'll be happy and it will have been done right. Sounds like you have the tools anyway. |
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Yep. The RAS does NOT clamp to the gas tube as a few people have mentioned. It indexes off of the barrel nut. If you have the tools, and assuming the nut is off the direction that you'd be tightening it to correct it, you could honestly do it without even removing the gas tube, so long as you're careful. Just put the wrench in place and apply a little torque until the nut moves slightly. Check it with the RAS, move again if need be. it may not "clamp" to it, but it does clip around over it. The clamp should not touch the gas tube i'm talking about the clip on top front of the HG. Gotcha. My post was referring to where the clamp on the RAS is, near the barrel nut. oh, yeah, the front tab should be under the Handguard tab, and it should be some pressure, then the Rear clamp around the gas tube. Yep, around the gas tube, but applying pressure to the barrel nut...not the tube itself. |
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