30.06 Headspace gauges need help

[Shiloh]

I just picked up some used 30.06 ACK GO/NO GO gauges because i want to build a 1918 BAR. I decided to try them out on a Winchester M70 and see what happens. Well' it wouldn't close at all on the GO. That was really weird. I put the NO GO in just to see what would happen. Same thing. I thought there may be something wrong in the rifle chamber so I brought out a 1903a3. Same thing. The GO gauge will not seat in the chamber all of the way.

Is there something I'm missing? Is ACK a special 30.06? I tried to look it up but couldn't find much info. I thought ACK was an older brand and decided to pick them up cause they were fairly inexpensive. They are both in great shape with no rust.

Any ideas??

[tujungatoes]

30-06 ackley improved is a modified cartridge/chamber. those gauges will not work on a standard 06 chambered rifle.

[Shiloh]

Ahh, that would make sense. I thought ACK was a manufacturer. After looking up what you mentioned it all fell into place. Well at least I didn't spend a fortune. Thanks for the info.

[kendog4570]

Most Ackley chambers were designed to be shorter than the cartridge that is "improved", to facilitate firing factory ammo in an improved chamber. So should the gauges be shorter. BUT, there is no standard for most Ackley stuff so there is really no telling what you may have. Your gauges should close with room to spare, but they don't. Big red flag. Is there a makers name on them?

On the BAR, you really need the US Ordnance specs as to which 30 cal gauges were applicable to that particular weapon. I don't have the data in front of me but there is quite a spread in the minimum and maximum head space datum for those gauges, and I would make a small wager that an auto weapon like the BAR would be somewhat looser than 30 cal rifle or sporting chambers. SAAMI min and max is a difference of .010", and .30 rifle chambers are usually .008" from go to field. Uncle Sam has specs for .30 cal chambers in machine guns that are well over the SAMMI max. Be very careful here.

ANY gas gun is more dangerous with head space that is too tight, rather than too loose. Partial, slam, and out of battery fires are often catastrophic to the gun, and maybe the shooter.

[Shiloh]

Good to know. The receiver is new from OOW along with the bolt and trigger group. The barrel will be had from a kit, when I can find one. Who knows what the chamber specs will be. Any little bit of info helps though. Thank you all.

[Junkie]

Most Ackley chambers were designed to be shorter than the cartridge that is "improved", to facilitate firing factory ammo in an improved chamber. So should the gauges be shorter. BUT, there is no standard for most Ackley stuff so there is really no telling what you may have. Your gauges should close with room to spare, but they don't. Big red flag. Is there a makers name on them?

On the BAR, you really need the US Ordnance specs as to which 30 cal gauges were applicable to that particular weapon. I don't have the data in front of me but there is quite a spread in the minimum and maximum head space datum for those gauges, and I would make a small wager that an auto weapon like the BAR would be somewhat looser than 30 cal rifle or sporting chambers. SAAMI min and max is a difference of .010", and .30 rifle chambers are usually .008" from go to field. Uncle Sam has specs for .30 cal chambers in machine guns that are well over the SAMMI max. Be very careful here.

ANY gas gun is more dangerous with head space that is too tight, rather than too loose. Partial, slam, and out of battery fires are often catastrophic to the gun, and maybe the shooter.

I thought the Ackley chambers were typically blown out somewhat, so you could fire a standard cartridge to fireform the case to AI. If the Ackley chamber was shorter, you wouldn't be able to use factory ammo.

I could be wrong though, never dealt with it.

[kendog4570]

Good to know. The receiver is new from OOW along with the bolt and trigger group. The barrel will be had from a kit, when I can find one. Who knows what the chamber specs will be. Any little bit of info helps though. Thank you all.

I would ask the Ohio Ordnance folks. I could be all wet, but MG chambers are usually quite a bit looser in the head space dept.

[kendog4570]

I thought the Ackley chambers were typically blown out somewhat, so you could fire a standard cartridge to fireform the case to AI. If the Ackley chamber was shorter, you wouldn't be able to use factory ammo.

I could be wrong though, never dealt with it.

A SAMMI go gauge becomes an Ackley no go gauge. An Ackley go is .004" shorter than SAMMI go. The idea was for the chamber to be a bit shorter so all factory ammo would bear at the neck/shoulder junction and provide an acceptable head space condition to fire form brass to the improved chamber dimension. The body tapers are usually lessened and the shoulders moved forward and have a steeper angle.

Again, Ackley chambers have never been standardized, with the exception of the 280 Ackley. There is no telling what someone may have improved upon his improvements. According to the man himself, a 30-06 AI shoulder datum at .375" should be .004" less than the sporting go dimension. Sure doesn't look like it in tujungatoes' picture.

[tujungatoes]

Not my pic. Just something puled from google for a visual. It's supposedly 06 and 06AI, but could be anything.