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Discussion in 'Technical Questions & Information' started by bigbluetruck, Feb 13, 2012.
Im wondering if i can use .223 headspacing gauges in a barrel marked for 5.56?
why would you need to? did you separate the barrel from the hood?
building my first upper and just wanted to double check to make sure everythings ok
Ah got ya.
ARs are modular. if you bought a barrel that already had the hood fitted then the headspace has no choice but to be right. Just seat it in the upper and torque the barrel nut to 80 ft lbs.
Now shilen match barrels come with a matched bolt head and have perfect match grade headspace. but the assembly is the same. and the system is still modular.
You can use a loaded cartridge to check headspace. Just put a slice of scotch tape over the headstamp and chamber the round. It should chamber and extract smooth by itself, and should get a little tight with 1 slice of scotch tape on the headstamp, 2 slices of scotch tape should not let the bolt close at all without excessive force.
Scotch tape is .002" thick and the difference between a go and a no go is .004".
Thatll save you the dough for a set of guages.
The difference between the two chamberings is the throat, which has no bearing on a headspace gauge. That said, headspace gauges from different manufacturers can vary a couple of ten-thousandths and there is also a couple of ten-thousandths difference between military headspace gauges and civilian headspace gauges, both marked 5.56x45.
It's all hooey. Temperature buildup as you repeatedly fire the rifle can make that much difference in headspace.
If the barrel extension was installed by the barrel manufacturer and the locator pin installed the headspace is fixed. We periodically check headspace on our Standard Series builds (where we purchase barrels with extensions already installed) but have never had an issue. Never.
80 lbs of torque is the recommended setting for GI armorers installing GI-style barrel nuts. If you are installing a free-float rail system, you will be using between 35 and 50 pounds of torque. Use plenty of anti-seize and tighten/loosen/tighten until you get the gas tube clearance in the desired torque range.