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12/18/2006 8:55:37 PM EDT
Can someone throw a mike on the barrel extensions outside diameter for me?  Or what is the hole diameter to be bored into the front of the upper for the extension to fit into?
Thanks
12/18/2006 9:15:00 PM EDT
[#1]
I have 2 uppers and both hole diameters measure exactly 1.000"
12/18/2006 9:26:11 PM EDT
[#2]
Extensions I have checked were 1.000 and the receiver bores have ranged from 1.004 to 1.007
12/18/2006 10:49:15 PM EDT
[#3]
Thank you
12/20/2006 2:13:44 PM EDT
[#4]
Extensions measure from 0.9984" to about 0.9996".
This is measured with a good mitutoyo 4.5 decimal place digital micrometer.
I have measured dozens of extensions and most fall within this range.

Extensions WITHOUT a barrel installed are usually smaller.
The extension tends to stretch at the front due to being torqued on to the barrel.
For this reason, the rear of the extension is usually smaller than the front by several tenths.
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