OzFclass

Hi guys,
Anyone who had chambered a 260ai did you use a go guage or crush fit to a saami spec 260 case?

A 243 AI go an nogo will work

Not a fan of crush fit.

Correct me if Im wrong but with AI chambers, the no go of a standard case becomes the go gauge. You can then get proper gauges to suit for no go, or on his video for chambering championship barrels, Gordy Gritters uses a piece of sticky tape over the base of the go gauge to give that extra couple of thou thickness required.

williada wrote:Not a fan of crush fit.

Why?

I believe it is the other way around brad. It seems the 308 go guage is the same as an ai no go.
the reaso I ask about the crush fit is for fireforming brass without a projectile. I already have lapua 260 brass which I plan to use.

Ackley cartridges are generally set up for a slight crush fit (1-4 thou) so that the parent cartridge can be fireformed without having to jam the bullet. This is generally on hunting rifles to that you can buy off the shelf ammo from a gun store and fire it without the risk of the cartridge sliding forward when the pin hits it !!Using a 308 or standard 260 Headspace will give this effect on chamber dimensions. Target can be a little different depending on what reamer spec you have. Ackley dies vary greatly in headspace dimensions as well so don"t ever take for granted that all Ackley"s are the same!! I know that the redding 260AI dies are made with PTG print 417 and the die is headspaced for a MATCH Ackley Headspace. My Gunsmith ( Dave Kerr) has a Ackley match headspace gauge which he uses on my 243 and 260 AI barrels and it sets up perfect for the Redding dies. The difference in using this Headspace gauge as to compared to a 308 or normal 260 gauge is 27 thou longer in headspace for the Match chamber. We have 3 guys over here in the West who have just discovered this in the last few weeks while getting 260 AI barrels done. If you use the 308 gauge and wish to use the Redding dies you will need to take 30 thou either off the bottom of the die or the top of the shell holder or the die will not go down far enough to bump the shoulder. We have also found that using a 308 gauge to headspace 260AI that brand new Lapua 260 brass would either not chamber or was extremely tight to chamber and the crush was too much. If you have custom dies which you may have got with your reamer then this problem will not occur as you can size the brass to suit your chamber specs. If you are trying to run off the shelf Dies (Redding) then the longer Match headspace is required if you don"t want to do any modifications to your dies!! I can also say that the Lee Collet die works fine with this Match headspace as well...

John, I am a pedant. I used the improved go gauge which matched my reamer from PTG. I simply soft seat the projectile to hold the case in place to allow fire-forming to take place and don’t rely on crush methods used on hunting rifles to fire-form cases for future use. My feelings about the crush fit stem from full bore experiences with issued ammo and also apply to negative headspace and repeated crush fitting.

edit: I'm taking this line because Dummos or others could be using a case for measurement of headspace which not very accurate. Also I think Brad's point is right, in that the no go gauge is .004" longer than the go gauge so it can be used as the go gauge of an Ackley chamber. By adding tape to the end of the "new" go gauge he would create a new "No go Gauge" for practical purposes if it did not get to that extra .004"

Those of us that used the issued brass with a crush fit in an endeavour to centre our projectile in the sloppy old chambers we used thought we gained in accuracy. What we did do is use the bolt to form our cases because we couldn’t reload. Many of us saw the damage that was done to the six o’clock lug from the wear and tear over time. No names no pack drill, but a prominent armourer pre 1980’s forgot to allow .002” on the barrel joint when drawing it up, so effectively gave the headspace a crush when the barrel was drawn up to tension. In an international match, with changed, harder brass, some would not go home. With factory rounds, the real effect was changing the tension on the receiver barrel joint which altered vibration and group because all brass was not the same even if we thought we were in a positive way pre-loading those joint threads for accuracy as well. Even with reloading - with more firings, the brass flow and case hardness alter unless you anneal and trim. This is why bumping the shoulder back a .001” worked to mitigate against those joint variables as we made the transition to reloading.

With reloading, the cases fire-form to the chamber for a general best fit anyway, so align the projectile better. The need to crush fit for this purpose is not necessary because we can jam fit the projectile if we want it centralised in a soft seat and not worry so much about a parent case in the case of a wildcat sliding forward as the pin hits it. I would think the case needs to be fire formed off bore alignment, rather than lower body alignment for a more precise fit because it will hold a spring back memory.

If people do anything out of the ordinary, even with the NRAA insurance, by not using an armourer who should follow accepted commercial procedure, this risk is on your head irrespective of accuracy obtained.

I agree there was a certain amount of creative chambering that went on in the past & I guess that Radway Green have a lot to answer for there. However, there seems to be a cogent argument in the BR fraternity that soft seating an/or making a dummy shoulder on the neck is not sufficient to create a 6PPC in one firing. By coincidence, when fire forming my 30/284 brass recently, I found that the light crush fit of my gunsmith's chamber with Lapua brass (we set it up with a Nosler case because...) resulted in drop-out-of-the-chamber brass after firing & no subsequent chambering issues.

John, I normally allow a few firings for my cases to settle, so to me a single firing is not so much an issue. Perhaps the walls were a tighter fit around the lower body of the Lapua for crush rather than headspace induced crush. If this was the case your bolt acted like the ram on a press. It works fine if it is slight pressure and your lugs are greased. The cases would drop out beautifully on first firing as they tend to shrink a tad and certainly would not present any re-chambering issues. But ask yourself is that neck, (not the shoulder), aligned centrally, the best it can possibly be for future precision seeing a projectile is not jammed to align it to create a brass memory? I don't think the headspace is that critical in future reloads because we bump it back .005" - .001". But once fire formed the case walls have a different role in centralising the projectile more effectively. But I am probably obfuscating.

I also know some people grease their cases while fire forming, some use reduced loads, some use dunny paper to retain powder rather than using a jammed projectile. To me grease on the case puts all the pressure on your bolt head and is a no no. The dunny paper has a better alternative use. I like to anneal the case, jam using a lighter projectile and a decent charge of powder to reduce the wrinkles. Next couple of loads are milder to allow for the case to harden, then I trim to length and use full bottle loads thereafter. This wildcatting is a lot more work. But each to their own. David.

this will be my first non standard cartridge so i value all input. while i already have the 260 lapua brass, what i really want to use is the palma brass. i have made .260 brass from 308 before so no hassles on that score. i already have a 260 lee collet die and a small body die, going to run the AI reamer through my 260 forster ultra seater.