A friend just received a new .25-06 Ack. reamer and both headspace gages. I saw that the shoulder angle of the gages did not match the shoulder angle on the reamer. The reamer has the 40 deg. shoulder but the gages have the 17 deg. found on the parent case. A call to the reamer grinder got an explanation that this is correct. I'm puzzled, I have a lot of reamer/gages and all of them have gages that match the reamer. To count on contact only at the shoulder/neck juncture seems wrong to me. An email to the reamer grinder did not get a response. What am I missing here? Thanks for any help, Jay

Jay---

The important measurement is the one that headspaces un-fireformed brass, not brass that's already been shot. The same is true of all the AI calibers.

It's normal to use the standard caliber GO guage MINUS .005 as the GO gauge for the improved version of the caliber. I've never heard of anyone buying a seperate guage for an improved cartride........to buy TWO of them seems a serious waste of money to me.

.....I'm the guy that's never owned a NO-GO guage is any caliber and see none in my future. I *measure* excess headspace, not guage it.

Jack,

I recall that one of the design features of the Ackley Imporved cartridges was the headspace datum was kept the same on the improved cartridge as on the original cartridge.

Also I thought the "no-go" guage was more use in aresenal screening or rifles for rework. I would expect gunsmiths to not need one.

So am I remembering correctly here?

jim dodd

HunterJim---

The headspace datum can be the same but the case should have some squash to it for safety. That's why the barrel has to be turned back on factory rifles that're rechambered to an improved case. Five thousandths seems to be the common amount of interference fit between Go and the chamber. A GO guage usually doesn't chamber in an AI chamber.

You're right on the guages. A NO-GO guage is great for those long days of barracks inspection of ATC M-14s.

I didn't buy the reamer/gages. I've made my own go gages for my .408 CT, 30-404 Jeff Imp (3 versions), 6 Dasher, 6 X 55 Imp., etc, only a "go" version. I've also "short chambered" a belted mag and bored the belt area out to give me a min. chamber at the shoulder. The problem that I have with the reamer/gages that I posted about is that they only touch the chamber at the shoulder/neck juncture. That just doesn't seem right to me. A full contace surface makes a lot more sense. I realize that one can go for "new case is snug" but which new case?

Hunter Jim,

The datum line being the imaginary point of reference on the shoulder of a non belted round is not the same with the Ackley improved version as it is with the parent cartridge, it is the neck/shoulder junction that remains the same. With the Ackley version as well as most all the other improved designs where a standard parent cartridge is the basis, the cartridge is firmly supported at the neck/shoulder junction for fireforming.

Upon firing, the shoulder pivots forward off this junction to assume the new 40 degree angle as the rest of the body blows outward. The -.004 crush that is often refered to with the improved chambering takes place at this junction.

To properly set the headspace on the 25/06 Ackley chamber, you need only set the length of the chamber to the point where the bolt will close with slight resistance on a standard factory case, or, with a -.004 crush.

Regards,

Malm

Go gauges for Wildcats: Beeeeeg Pandora's box.

I have a few Ackley gauges, with a 40 degree shoulder. They are ground to the correct length of 0.004" shorter than the parent cartridge. I don't use them, I do like everyone else and chamber for a 0.004" or so crush on the brass. Be careful with the brass, it all ain't the same length!! Sort & Measure.

Here is one for you: For one of the big 338 Wildcats, I have two reamers with different neck sizes and two headspace gauges. One gauge is 0.018" longer than the brass, the other gauge is 0.036" longer than the brass.

So, why the difference? Both gauges are generous, as the chambers and cartridges are to be set up for fire forming with the bullets hard into the lands. The reason for doing this is powder capacity.

This situation is risky for the unknowing. Chamber for the gauge, and fireform with the bullet away from the lands, you are in instant trouble big time.

Moral of the story: Measure, measure, measure. If a person is new to the chambering game, proceed carefully and ask for help.

[ 05-11-2003, 08:22: Message edited by: John Ricks ]

I agree with Mr Ricks, cases vary between brands.

Once about 25 years ago I chambered a 6mm Ack Imp. I used brand new Win unprimed cases to set it up with .004 crush fit.

Well the customer come back mad as old wet hen. Seems he had bought a lot of Rem brass. They where about .006 shorter than the Win cases. To make a long story short. I simply set the barrel back to fit his cases.

A couple of things about headspace gauges. You DO NOT have a go of one brand, and a no go of a diferent brand. Make sure both gauges are the same brand.

Also you use great care when closing the bolt. You can crush the metal in the chamber with the hardened gauge. I have seen it done.

The first thing that I do when using a new reamer is to make a "gizzy". Some call this a bullet seating gage. It is a short piece of barrel that has had the reamer run in far enough to have most of the shoulder present. This tool is an aid in making or measuring headspace gages, brass, resized brass, you get the picture. Just measure over the gizzy and case/gage with a caliper and you have a useful dimension. These tools are also very handy in setting up dies, bumping shoulders, matching chambers in barrels, etc.
The next step is often making up a surrogate barrel with headspace .002-.003 SHORTER than the finish barrel. This has really saved barrel wear on our Dashers, .30-404 Jeff, .30-.338 Lapua Short/Imp and 6 x 55 Imp. chamberings.