What is Air Gauging?
What does it mean when they say a barrel is air gauged?
"My faith, my country and my family will guide me; nothing more, nothing less" -Gen. Tommy Franks
"My faith, my country and my family will guide me; nothing more, nothing less" -Gen. Tommy Franks
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Air gauging is a method of measuring where air flow through a precision orifice as modified by the clearance between the orifice and the measured part is measured.
In the case of a simple cylinder sleeve the measuring probe is a disc about an inch thick to prevent tipping and thus error with the precision orifice at mid length of the disc. The disc rests against the side opposite the orifice and the clearance between the disc and the determines the ari flow and thus the size. This kind if gauge is calibrated by inserting into a master ring before each use. We used this kind of gauge for cylinder sleeve boores and piston pin bores where the tolerance was +/- .0005 for the seeves and +/- .0001 for the piston pin bores.
Federal made theauges we used. See a photo of a modern digital gauge at:
http://www.deterco.com/products/Mahr Federal/new/mahr_micro_dimensionair.htm
Obviously a very special plug would be needed for a rifled bore.
This kind of gauge would not only show size but could also show variations in diameter along the length.
John Stimson, Jr.
www.histandard.info0 -
The above is a good explanation of air gauging.
While the air gauge can measure (indirectly) the variances in barrel size, one of the things that determines the quality of the barrel is the "allowed tolerance". If you look at the specs for a Shilen (just as a example), you will see that they hold tolerances in the millenths (.0001 = 100 millianths of a inch) and give you the choice of grade, while another company that touts there "air gauged" barrels dosn't give you the variance limit (.0005 or .005) that they hold to/reject at.
Another interesting thing to do, is look at the borescope video that's on the Lilja barrels website. It will give you another perspective on barrel quality. http://www.riflebarrels.com/default.htm Look for the link to the video (choice of connection speed).
Some guys like a mag full of lead, I still prefer one round to the head.0 -
Cool video. Thanks for the info guys.
"My faith, my country and my family will guide me; nothing more, nothing less" -Gen. Tommy Franks0 -
Tailgunner, I could be mistaken, but I believe .0001 is actually one ten-thousandth of an inch. One millionth would be .000001, but now we are splitting hairs.[;)][;)][:D][:D]
A BAD DAY OF HUNTING IS BETTER THAN A GOOD DAY AT WORK!
ONE HIT IS BETTER THAN 10 MISSES!0 -
quote:Originally posted by farfromnormal
Tailgunner, I could be mistaken, but I believe .0001 is actually one ten-thousandth of an inch. One millionth would be .000001, but now we are splitting hairs.[;)][;)][:D][:D]
We are both correct actually, .0001 is commonly refered to as 1/10 thousanth, but if you write it out in properly it's 100 millianths (0.000,100").[;)][;)][:D][:D]
Some guys like a mag full of lead, I still prefer one round to the head.0 -
quote:Originally posted by farfromnormal
Tailgunner, I could be mistaken, but I believe .0001 is actually one ten-thousandth of an inch. One millionth would be .000001, but now we are splitting hairs.[;)][;)][:D][:D]
A BAD DAY OF HUNTING IS BETTER THAN A GOOD DAY AT WORK!
ONE HIT IS BETTER THAN 10 MISSES!
It's machinists shop talk to call it 100 millionths. Like they refer to .010 inch as 10 thou.
Even so, I'm curious to see how Shilen barrels measure up with such tight tolerances. Equipment that precise is extremely expensive and to keep that kind of tolerance.....I'm curious if it's just hype or not. I used to do a lot of stuff for Allied Signal in Phoenix Az where they make APU's for commercial airliners, I don't remember their tolerances even being that tight on turbine engines.0
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