7x57AI fireforming

[shimoda]

Could someone guide me through the process of creating a false shoulder on my parent cases for fireforming to the improved chamber?
So far I have fired mid range parent case loads set to SAMMI COAL, and I have also used the Cream of Wheat method.
The gun is shooting well but I had a case head separation on my second firing of a formed case. Upon close examination of my formed brass I can see a brighter ring around the formed cases just above the case head and from what I've read this is an indication of too much headspace and imminent case head separation.

The brass I've been using is Winchester that I purchased as "once fired", but for all I know it was fired many times. I did not anneal it prior to starting this process.

I thought the brass might be toast so I bought new Norma brass. I have fireformed a dozen pieces and it seems (could be my imagination) that I can see a slight, brighter ring around these new cases. I'd rather not take a chance on ruining any more of these new cases.
I've read that jamming the bullets in the lands is not a strong enough solution which is the reason i would like to "crush fit" by using the false shoulder method.
This rifle does not have a tight neck chamber.

The dies I have are RCBS 7x57 improved Full Length and seater dies and a Redding 7x57 improved series D neck die.
I have dies for lots of other cartridges but the only dies larger than a .284 is 30-06 and 444. I have no bushing dies. Most of my neck sizing in the other cartridges has been with a Lee neck collet sizer.

This is my first AI chambered rifle.
Thanks in advance,
Sam

 

[Mikecr]

I'll have to think on it but right now I can't see a way to do it without a bushing die. False shoulder would be tough given that the next cal up is actually 2cals up(too much).
There is an inverse approach;
With a bushing die you could choose big undersizing past seated bullet bearing. This would leave an internal shelf for a seated bullet to press against while jamming into the rifling. It would take a helluvalot to seat the bullet any deeper, as you would notice while seating, and use cheap bullets that you can jam with(this much seating force isn't good for bullets).

Bushing dies are nice, and this I believe would solve the issue at hand.
Once fireformed you would go back to a normal sizing bushing.

 

[shimoda]

I'll have to think on it but right now I can't see a way to do it without a bushing die. False shoulder would be tough given that the next cal up is actually 2cals up(too much).
There is an inverse approach;
With a bushing die you could choose big undersizing past seated bullet bearing. This would leave an internal shelf for a seated bullet to press against while jamming into the rifling. It would take a helluvalot to seat the bullet any deeper, as you would notice while seating, and use cheap bullets that you can jam with(this much seating force isn't good for bullets).

Bushing dies are nice, and this I believe would solve the issue at hand.
Once fireformed you would go back to a normal sizing bushing.

Mikecr- Thanks for the reply. So if I used a bushing die to reduce the neck substantially, wouldn't I then have to expand a portion of the neck to accept the bullet? Or are you saying just jamb the bullet part way (thus the cheap bullets) which would create the shelf?

Next question is if I can't find a bushing die specifically for 7x57imp, can I use one for another cartridge? I guess I need to find a diagram of a bushing die to see how they work.

Thanks, Sam

 

[westcliffe01]

Are you positive that the rifle is headspaced properly ? Are you sure that you are not sizing the brass too short prior to loading ? Any "proper" Ackley should be fairly tight to close the bolt on "regular" brass since the shoulder / neck intersection should be a few thousandths longer than the Ackley chamber.

It sounds like the brass you are using is too short to the end of the shoulder or your chamber is too long. Did the person who set up the barrel do it right ? I suggest you go to Mansonreamers.com and get the Ackley "GO" gauge that you need and check the head space. The real Go gauge will have the right shoulder angle and length and you can see how the bolt closes on it. Then go from there to solve the problem. I mention Manson since they are the only source I know which typically carries stock of ackley gauges. I personally do not like using a regular gauge on an ackley chamber. Too much risk of damaging the chamber with the unequal shoulder angles and just having a line contact at the base of the neck.

 

[MNbogboy]

As a spin-off on Mikecr's reply...Can you simply remove your sizing button (stem), size the neck without it and then reinstall the button and only expand as much as you need to start the bullet and still achieve the high seating force to maintain a well jammed bullet?....
I have 3 AIs (two 257 Bobs and a 6.5 Bob)...A jammed bullet was required with one of the 257s before I adjusted the of head space, but I never did have a problem with cases stretching like yours....I bet if you jammed them the way they are you very likely would see less or eliminate your head separation issues.
BTW I have never used the COW method only have used "cheap" bullets (there is no such thing as cheap bullets)!
Good Luck,
Randy