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AR15.COM
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3/23/2009 8:30:44 PM EDT
I'm looking at doing a mid-length barrel.  I've searched and found alot of general information on the mid-length gas port location (about 9")

but does anyone know the exact measurement, say from the breech or the barrel extension?

thanks!!
3/23/2009 9:58:34 PM EDT
[#1]
From AR15barrels:

From the barrel torque shoulder where the barrel extension torques against, it's 6.75" for carbine, 8.75" for mid-length and 12.125" for rifle to the step at the rear of the gas block seat.
Breach face is 3/4" back from the torque shoulder.
Gas port is usually 0.275" to 0.295" forward of the rear step, depending on if there is a handguard cap in the design or not.
You should be able to figure everything else out from that...
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I built a midlength according to these measurements, and it functions just fine.
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