View Full Version : Colt 6920, geissele mk8 rail install, barrel not centered.
New Colt 6920, I shaved down the fsb, and installed a new mk8. The barrel is not centered inside of rail. It's approx 1/2 a millimeter off. I took a straight edge to the rail and upper, it seams dead on, both sides. I'm thinking it must be the receiver face.
Is this fairly common? Should I buy a facing tool?
http://i24.photobucket.com/albums/c25/Dirknar77/Mobile%20Uploads/20160928_093127_zpst7w46hyj.jpg (http://s24.photobucket.com/user/Dirknar77/media/Mobile%20Uploads/20160928_093127_zpst7w46hyj.jpg.html)
Doesn't matter. Get to the range and zero it.
Ok will do. Just annoying? What about iron sights mounted on the rail? The pic makes it look better than it looks with naked eye. You can tell its crooked. (Kinda like hillary,bam! )
Dirknar,
Shoot us a few more pictures at sales@geissele.com along with some more information about the upper. If there is an issue with the rail, we will get you squared away.
-Geissele Customer Service
Wow! That's customer care,right there! I bought a geissele ssa trigger for it too! Glad I did!
Ok will do. Just annoying? What about iron sights mounted on the rail? The pic makes it look better than it looks with naked eye. You can tell its crooked. (Kinda like hillary,bam! )
This is why you have adjustable sights.
1/2 mm = almost .020 so you are .010 off center. If it bothers you that much give the rail a whack with a rubber mallet. If you don't have a rubber mallet just slap it against the nearest tree.
I hear you, but the rail is straight. It's the barrel that's crooked. Here's a better pic of how obvious it is.
http://i24.photobucket.com/albums/c25/Dirknar77/20160928_143826_zpspmgzl1oo.jpg (http://s24.photobucket.com/user/Dirknar77/media/20160928_143826_zpspmgzl1oo.jpg.html)
And here's a pic of a straight edge. It is dead straight all the way down both sides of the rail and receiver, with optic removed as well.
http://i24.photobucket.com/albums/c25/Dirknar77/20160928_144032_zpslqsqm3zr.jpg (http://s24.photobucket.com/user/Dirknar77/media/20160928_144032_zpslqsqm3zr.jpg.html)
I know there is some knowledgeable people on this forum. you guys say, no biggie, shoot it, then that's what I'll do.
I might buy that receiver lapping tool in the future though, it seems cheap enough and couldn't hurt in a quality build.
A measurement with a pocket ruler and a rusty framing square isn't enough to convince me something is off. You are wrong about the lapping tool doing no harm. Think about how it is used. How can it work? A lot of tools in the Brownell's catalog remind me of stuff in the J. C. Whitney catalog. If I order 5 things that increase my HP 20% I can double my motor's HP. I don't think so.
Haha ya, I had that one coming.. pretty crude measuring devices. When handling the rifle, you can plainly see that the barrel is crooked, that is all..
Why I am not in the firearms industry thread.
A measurement with a pocket ruler and a rusty framing square isn't enough to convince me something is off. You are wrong about the lapping tool doing no harm. Think about how it is used. How can it work? A lot of tools in the Brownell's catalog remind me of stuff in the J. C. Whitney catalog. If I order 5 things that increase my HP 20% I can double my motor's HP. I don't think so.
You can still see by looking at the photos with your eyes that it's off. Whether or not the framing square is rusty doesn't matter. It's still a straight edge and clearly shows that there is an issue with the barrel and not the rail.
steyrman13
09-28-16, 22:25
This is no where near as off center as some other rails and barrels sit. It is not where close to a problem.
Are you trolling?
Haha no I'm not trolling.. I've been signed up on this forum for a few years now.
It's a little crooked and I wanted to know how common it was, and its kind of annoying that's all.. no worries, I'm gonna get it sighted in and have fun with it.
1/2 mm = almost .020 so you are .010 off center. If it bothers you that much give the rail a whack with a rubber mallet. If you don't have a rubber mallet just slap it against the nearest tree.
Oh ya and the 1/2 mil estimate was already cut in half. It's actually a millimeter off from the other side. That's why I figured it was roughly 1/2 millimeter off.
Geissele is so precise with everything he does he would probably take your upper in and perform an analysis over the course of a few weeks and design the next generation of rail around the .5mm off-centeredness.
I had a similar issue with my BCM upper and NSR rail. I sent it in to BCM and they worked their voodoo magic on it. bottom line, I dumped well over a thousand dollars into my rifle and it will at the very least be straight. Something is clearly out of tolerance somewhere.
Wolfpack45
09-30-16, 09:07
More than likely the receiver face as you suspected. I have assembled hundreds of uppers and that has been the problem each time I have encountered this issue. Try truing the receiver face or replacing the receiver and see if that fixes your problem. Only other thing I would double check is the barrel extension, caliper the lip around the barrel extension that interfaces with the receiver face and make sure everything is good there. Depending on how bad the angle is that the barrel is off center, zeroing can become problematic or even impossible, especially with irons (however yours doesn't look bad enough for this).
Jailbirdwatcher
10-10-16, 20:03
I had a similar problem with a Black Rain Rail assembly. My BUIS had to be adjusted all the way to the right to put my hits in the target center. I used an EO Tech sight on it and had to crank the windage on it also. The barrel was definately off centered in the the fore end rail. I then lapped the receiver, but it helped very minimally. My next move was to replace the rail with a Geissele. This move made quite a difference as the barrell appears to be on center. However the rear sight is cranked a little further to the right than I want it to be. The EO Tech remaind on target with no further adjustment. Just thought I'd post this experience as it is a bit like the problem of the OP.
Someone please lock this thread.
Update: for any interest..
I called Colt and asked them about this issue. They said to shoot it, if it doesn't group 4-5 moa, then they would take a look at it.
I went shooting the other day, but it was really windy, rainy and I had no good spot to shoot groups. The only thing I did before hand was, the old eyeball boresight across the street to get the red dot as close as I could. I was hitting a 8" x 12" plate at 100 yards without touching the sight, figured it was close enough for that day.
Update: for any interest..
I called Colt and asked them about this issue. They said to shoot it, if it doesn't group 4-5 moa, then they would take a look at it.
I went shooting the other day, but it was really windy, rainy and I had no good spot to shoot groups. The only thing I did before hand was, the old eyeball boresight across the street to get the red dot as close as I could. I was hitting a 8" x 12" plate at 100 yards without touching the sight, figured it was close enough for that day.
Excellent.
Worry less, shoot more! :smile:
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