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1/11/2017 10:02:00 AM EDT
Guys,

Have a 14.5" Colt, non-FF, been a minute of angle gun for last 10 years or so.  Wears a Mark 4 3-9 and has been consistent for me during that time.  I added a MI FSB rail (the kind that bolts into the triangular space in the sight tower) with the intention of adding a light there, but had not yet installed a light -- the gun shot waaaay off, I had to come up 3 MOA and right 1 MOA in order to be back to zero.  At that point it was shooting MOA again.

I checked the scope mount, barrel nut, and a few other things.  The accuracy of the rifle has not changed, just the POI.  Wondering if adding the weight to the barrel in the form of an FSB rail has changed the harmonics such that it would explain the POI shift.  At any rate, I've removed the rail and will shoot the gun again tomorrow to see what's what.

Thanks.
1/11/2017 3:58:44 PM EDT
[#1]
I've seen POI shifts that large just from new muzzle devices.    A rail causing it isn't surprising.
1/11/2017 4:16:57 PM EDT
[#2]
Quoted:
Guys,

Have a 14.5" Colt, non-FF, been a minute of angle gun for last 10 years or so.  Wears a Mark 4 3-9 and has been consistent for me during that time.  I added a MI FSB rail (the kind that bolts into the triangular space in the sight tower) with the intention of adding a light there, but had not yet installed a light -- the gun shot waaaay off, I had to come up 3 MOA and right 1 MOA in order to be back to zero.  At that point it was shooting MOA again.

I checked the scope mount, barrel nut, and a few other things.  The accuracy of the rifle has not changed, just the POI.  Wondering if adding the weight to the barrel in the form of an FSB rail has changed the harmonics such that it would explain the POI shift.  At any rate, I've removed the rail and will shoot the gun again tomorrow to see what's what.

Thanks.
View Quote


Adding the rail section to the FSB changed the harmonics slightly. It is never advisable to hang anything off of the barrel as it can affect accuracy. This is where having a free-float handguard is advantageous.
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