What is acceptable runout on bore/extension?

[mg]

I have test fit my beautiful new .308 barrel into a Mega monothic upper.

I noticed there is a definite downward tilt to the barrel. To determine whether the issue is with the barrel or the extension socket in the upper, I rotated the barrel in the socket.

It looked like the axis of the extension is not the same as the axis of the barrel.

With the barrel in normal position, I measured from the top of the rail to the barrel, and then from the bottom of the rail to the barrel. I then rotated the barrel 180 degrees so the gas port pointed down. I measured from top and bottom again and came up with a .100" difference between the two measurements.

I repeated the check from side to side -- turn gas port to 3 o'clock, measure then turn gas port to 9 o'clock, measure. It comes out to roughly .100" change from side to side as well.

I understand the extension is short and the mating/locating surfaces are small. Is .050" runout over 12 inches acceptable?

Thanks

[GLSHOOTER]

Are you sure the upper is square where it meets the barrel extension or would that not have an effect on this?

At a guess I don't think 0.050 in that distance. would be unheard of in any of the rifles we see by various makers. I don't have the ability to check mine but I am hazarding a guess that you won't see any downrange issues with it.

I'm sure that someone that is in the know on machining tolerance will chime in.

Greg

[dr69er]

Up to .005" R/O is acceptable...w/ .010" about absolute Max.

There should be a sliding fit between the barrel extention and
forward upper reciever at most, w/ a light press fit on the over
end of the spectrum...