AR Sponsor
Posted: 12/31/2010 2:57:39 PM EDT
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Couldnt find a whole lot of info on this, some say they have built 20 AR's and never heard of the tool, others say it is a must. I am building a precision 6.5 Grendel and while I am sure it dont make your gun shoot .5 MOA better, but is it worth the time and money to get this tool?
Upper receiver lapping tool |
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I lapped the upper of my last build (with a tool from work) and glad I did. Lapping revealed the face of the reciever wasn't exactly perpendicular to the reciever bore. It was a minimal amount, but I wanted to do everything I could to improve accuracy. I almost bought the correct tool, but found a "special tool" at work that fit perfectly and used it.
Lapping may not improve accuracy, but it does insure the barrel and reciever are aligned. |
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I have one. I guess it just depends if you want to do everything possible to make sure your rifle is exactly as it should be. A rifle is just a machine after all. I've lapped six uppers now, IIRC all but one were off, out of square with the bore the carrier rides in, at least a little bit. Now I know that all my rifles/carbines have a barrel mounted as parallel as I can get them with the bolt carrier group. "one less thing" |
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Quoted:
I have one. I guess it just depends if you want to do everything possible to make sure your rifle is exactly as it should be. A rifle is just a machine after all. I've lapped six uppers now, IIRC all but one were off, out of square with the bore the carrier rides in, at least a little bit. Now I know that all my rifles/carbines have a barrel mounted as parallel as I can get them with the bolt carrier group. "one less thing" +1 It's no different than truing a receiver on a bolt gun. And yes, it will remove some of the finish. But it will be square to the bore as possible edit, mine did not fit on two MEGA side chargers |
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The internal diameters of some uppers may be undersized. It happens. Interesting it was Mega, were those billet?
Would I want my upper trued to mount the barrel as best possible, yes. Is it going to make any measurable difference for the average assembled gun? Likely not. The ability of the barrel to shoot a projectile consistently is largely based on muzzle vibration, a truly parallel bore, and no warpage off axis as it warms up. After that, the quality of the ammo. Then everything else - and if it's slightly off axis, it won't have a impact point exactly the same as the virtual bore axis, but it doesn't have one anyway. Windage and elevation true it up at range. Will it effectively do much, I doubt it, but I would do it, it's cheap enough. A builder who then shoots it can eliminate that as a cause of inaccuracy. He's left with the rest, tho. It's just one part of the build, not a cure all. Keep it in mind for what it can do. Makes me wonder, isn't this done before sending it out to be anodized? Or, does anodizing throw it off that much anyway? And why not on the Tier One stuff? Don't they sell the best stuff, and if they aren't doing it, why? Inquiring minds want to know. |
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Quoted:
sounds like a tool that is worth it and cheap insurance that the bore and upper receiver are parallel. Any recommendation on lapping compound? I use a lapping tool also .... have done several uppers to square them off. The lapping compound I use is from wheeler engineering .... purchased at Midway ....here. There are three types in this particular kit, they are 220-cutting, 320-smoothing and 600-polishing grits ... I have also used them for other applications such as lapping new barrel bushings to my 1911's .... well worth the money IMHO. WARNING!!! Go slowly and clean it off and check fitting of the barrel during the process .... if you use to much of the "cutting" grit and take to much off you can effect the alignment of your M4 ramps and create a "lip" between the upper ramps and the barrel ramps. This happened to me on the first one I did ... I started with the 220 cutting then 320 to smooth then I reinstalled the barrel and I had a slight "lip" on the feedramps. The next one I did I switched to starting with the 320 smoothing compound then going to the 600 to polish and it worked perfect ... no "lip" on the feedramps. |
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