This is a discussion on who can air guage a rifle barrel within the Gunsmithing forums, part of the M14 M1A Forum category; I am looking for a company who can air guage a few M1 garand barrels
I am looking to make a few NM rifles BUT ...
Air Gages are so VERY expensive that no gunsmith will normally have them. You might try contacting Krieger or Douglas as they MAY be able to do it for you. However, it WON'T be cheap and I am not sure it would gain you anything.
I air gaged hundreds of NM and standard M14 barrels and quite a few Garand barrels in the 70's and 80's in the Marine Corps. What counts is how the barrel shoots when it is installed in the rifle.
If you follow through on this airguaging please keep us in the loop. Sounds interesting to me.
Gus; Did you find barrels that had good airguage results that didn't shoot well and some that shot well with poor results?
I don't really know what airguaging is. I have an idea what it is and I could ramble here for a while, but that won't help.
Air Gages have long "wands" with compressed air going through them and different heads. Usually you have one wand for lands and another for grooves. When you turn on the air, you first have to use the precision round "doughnut" gages to set the air pressure on the tower gage. The gage reads by the pressure of the air bounching off the inside of the gage or bore of the rifle. We measured and recorded the measurements just forward of the breech, about 1/2 way down the barrel and finally right at the muzzle for both the lands and grooves.
The Art and Mystery of using Air Gages is really in setting the air pressure correctly with the precision round doughnut gages and taking the time to adjust the tower gage correctly by adjusting the air pressure. You have to be obstinate about setting that pressure correctly or your readings won't come out correctly. I have no idea why, but it was something I had a natural knack for doing and wound up gaging hundreds of barrels for that reason.
On NM "Light" or standard configuration barrels in the early/mid 70's - the standard for THE Marine Corps Rifle Team was no more than .0003" variation between ANY of the land or groove measurements AND they had to either be straight or taperted towards the muzzle. They did seem to shoot a tiny bit better that way than when they open tapered towards the muzzle.
However, in the 1980's when we began using Krieger Barrels, they hold a standard of no more than .0001" anywhere along the length of the barrel. To be honest, once we went to Krieger barrels, we stopped using Air Gages much at all. When I came back to the RTE shop in 1994 as the Shop Chief, I had to show most folks how to use the Air Gages as it had been so long since we had used them frequently. We actually used them more for the M40A1 Sniper Rifles then than for NM M14's.
A cheap mans air gauge would be using "00" buck shot (.33 dia.) Use a wooden dowel and as Gus said check the area ahead of the throat, muzzle, and mid section. To do this you use a dowel at the front and rear and compress same at that area. Your bumping up the lead to fill that area. Measure same with a set of mics. Push the 00 out the short travel, i.e., front out towards muzzle and breech towards the rear as to minimize any distortion of the measurements. As for the middle, I just run one 00 breech to muzzle and just feel how it slides. Not as precise as the AG but you get a feel for it after a few barrels. Also, don't forget to lightly lube the barrel. If you search the internet there are more detail articles of what I just described. I suggest reading them before slugging.
I once did a barrel, breech to muzzle, and the slug took off and stopped about 2" before exiting out the muzzle. It was for sure loose in the mid section! I was glad to note it was tighter at the muzzle. This was a BPCR barrel so it wasn't that critical due to the obturation of the 540 gr. lead bullet. BTW it does shoot well.
May I add with emphasis that Major Stuph advised to use a micrometer to measure the lead "slug" and NOT a pair of even the most expensive dial calipers. You really need the accuracy of a good micrometer to check this accurately.
Dial Calipers are great for comparing measurements and what a machinist might call a 'rough" precision measurement, but not a truly precise precision measurement. When you go to trying to read in Ten Thousandths of an inch, you MUST use micrometers.
I realize machinists and those who are serious hobbyists with machines know this, but the average person does not.
Sort of off topic. Have real machinists or extremely serious hobbyists ever used a set of digital calipers that were truly accurate and repeatable? Maybe I'm too "old school," but I have used three different sets without acceptable success at "repeat measurements" and always go back to my Starrett Dial Caliper.