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Posted: 12/31/2011 2:17:17 PM EDT
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I am building an M16A1 clone using a NDS Lower and a Colt parts kit. I installed my FSB and thought it was very straight, but it turns out it is canted a couple of degrees to the right of center. Is this something that can be corrected or will I just have to adjust my rear sight and chalk it up to inexperience?
Other than that and the lack of a disconnector in my kit, the build is coming along smoothly! |
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Is the FSB canted on the barrel? Or is the barrel canted in the upper receiver?
Excellent question! If only really a couple degree's off as in two or less it will probably be fine and probably actually within milspec. Problem is much more than that and you won't be able to hit anything over 250-300 yds without a lot of Kentucky windage. The fix will be shimming or peening the receiver which I don't recommend but it works if in the receiver. You can also re-torque and adjust to correct with a little over tightening if canted to right looking down barrel if it's the barrel FSB install. Usually best to re-torque the barrel first and see if you can correct. If only shooting 100-200 yds don't think I'd bother. No tick semi selector should be easy to find. I just bought a new production black CMT semi selector for $8 and three delicate naval jelly applications and it looks at least as good or better than my original Colt's. Not saying all CMT's are no tick but this one was. Might pick up a couple more sometime soon. Really waiting on tax time to see how much extra Obama wants. |
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If you installed your FSB with the tapered pins, then you can ream the holes/barrel cut out with a larger tapered reamer and install oversize pins (After fixing the FSB in the new position!). Tapered reamers can be ordered from Travers; tapered pins can be found in most any Ace hardware store.
I have the 2" long tapered pins, which give you a lot of latitude as to your hole size. I also have a full set of tapered reamers. Not a hard job. Clamping your FSB in the correct position is the biggest challenge. 
Edit - I would file the the barrel cuts with a 6" round file before re-reaming the FSB/barrel...
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is this one of those those non chromed, 1/9 twist, kit barrels that were sold in the white?
if it were mine I wouldn't screw up a good receiver to fix a problem with a fsb......fix the part with the problem, don't mess up a different part trying to compensate for the bad one In order of the way I would try and fix it would be: (1) remove and reinstall the barrel first and see where it ends up, if it's not off too bad learn to live with it (2) if it's still off enough to really bug you, remove and re-orientate fsb using slightly larger taper pins ETA: or trim the indexing pin if it will move the sight enough to fix the problem ....or (3) cut down fsb and use it for a lightweight tacticool rifle with an extended FF tube (or sell to someone who wants to build one )
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Some one posted that installing the barrel with the barrel clamped instead of the receiver changes POI but I don't remember the specifics.
One way to shift POI left and the other way to shift it right. Just coughin up a little chunk of memory. Someone that remembers will hopefully be along soon to give the real story. |
| I once bought a used RRA upper that the fsb was canted to the left...turns out whoever assembled it was a gorilla and had torqued it up without grease of any kind. The indexing pin was almost sheared in half by the receiver, but it still functioned fine, so you do have a bit of a fudge factor with the ramps (on a rifle extension anyway, don't know about those m4 ramps) |
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I've had a few builds require excessive windage adjustment to zero. One two the left and the other to the right.
I fixed both rifles by removing the barrel, cleaning everything, and then reinstalling the barrel using a receiver clamp and twisting the barrel in the direction i needed by hand while tightening the barrel nut with a wrench. Posted Via AR15.Com Mobile |
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