NEED HELP accuracy problem!!

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[ARCHIVED THREAD] - NEED HELP accuracy problem!!

Posted: 7/26/2002 4:09:01 PM EDT

Put together an A-1, all military, 20" upper. It shoots about 10 clicks to the left at 25 yards on a standard A-1 military target.

I do not have enough sight adjustment to get the groups centered up. Any suggestions? This is a really neat setup, but it sucks that it won't shoot well.

Is there anyway to tweak the barrel or something to get the sights lined up better? What would make the sights so far off?

Thanks

Posted: 7/26/2002 4:57:19 PM EDT

[#1]

455,
if you don't get an answer here, consider reposting down on Dave_G's "Maintenance & Cleaning Forum" - those guys that hang out down there are GOOD !

Posted: 7/26/2002 5:16:21 PM EDT

[#2]

There is a *slight* mis-alignment where the barrel is attached to the upper receiver, usually caused by the barrel rotating slightly as the barrel nut is tightened down. This is exactly the source of the problem with all of the Bushmaster "overtorqued" barrels.

You fix the problem by loosening the barrel nut and retightening it while preventing any barrel rotation. There is a pin on the barrel that fits a slot on the receiver. It may be necessary to file a bit off the pin, or if it needs to go the other way, to use a shim between the pin and the slot. A little square cut from an aluminum can works great.

Of course, you need a vice, action blocks, punches, and a barrel wrench at minimum. A gas tube wrench is also nice.

-Troy

Posted: 7/26/2002 5:17:52 PM EDT

[#3]

Quoted:
Put together an A-1, all military, 20" upper. It shoots about 10 clicks to the left at 25 yards on a standard A-1 military target.

I do not have enough sight adjustment to get the groups centered up. Any suggestions? This is a really neat setup, but it sucks that it won't shoot well.

Is there anyway to tweak the barrel or something to get the sights lined up better? What would make the sights so far off?

Thanks

As long as the bullet is not stricking the FS on the way out, this could be a easy fix.

The front sight is canted to the right as you look down the barrel. To fix the problem, remove the barrel and shim the trunion pin to pull the sight back to a zero index.

If you run out of room to shim, the trunion/barrel exstenstion may have been torqued wrong and the sight tower and exstention pin may be out of alinement. If this is the case, then you can remove the solid pins in the front sight and replace them with set screws to allow adjustment to the front sight tower.

Hope this helps

Posted: 7/26/2002 6:04:00 PM EDT

[#4]

I figured this was probably the problem. I'll get on it tomorrow.

You guys really rock. What a plethora of info.

Troy, as ususal. you the man.

Posted: 7/28/2002 8:23:45 AM EDT

[#5]

Your front sight is off-center. That is your front sight is rotated a bit off to the side; it's not in the "straight-up" position on your barrel. If you look carefully at your front sight you'll notice that this is the case. Once you get this rectified, by either shifting it yourself or having the/a factory/gunsmith fix it, your problem will be gone.

Posted: 7/28/2002 9:28:29 AM EDT

[#6]

Quoted:
Put together an A-1, all military, 20" upper. It shoots about 10 clicks to the left at 25 yards on a standard A-1 military target.

I do not have enough sight adjustment to get the groups centered up. Any suggestions? This is a really neat setup, but it sucks that it won't shoot well.

Is there anyway to tweak the barrel or something to get the sights lined up better? What would make the sights so far off?

Thanks

In the book "THE COMPLETE GUIDE TO AR-15 ACCURACY," BY Derrick Martin & Barrett Tillman, read "ZEROING PROBLEMS" on page 237, and look at the picture on page 238.

Bill

[ARCHIVED THREAD] - NEED HELP accuracy problem!!

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