What's the old rule of thumb? e.g., Fastest powder at [minimum OR maximum] published charge weight?

I have 35 Whelen brass I want to do in my AI chamber. Was thinking of using 3031.

In my 257 AI I've always chosen a load that is on the upper end for the standard cartridge and they've worked well.

The other way you can go, throat allowing, is to use a relatively mild load for the standard chambering and seat the bullet into the rifling to ensure correct headspacing. That'll create enough pressure to form the case, too.

Good luck!

The best way is using a fairly hot full charge load this insures the case will be formed properly or as close to your chamber as possible.

You usually not going to get a fully fireformed case after 1 firing which is why a close to max or at max charge will give you the best results, and gives you more consistant results from the 2nd to 3rd firing.

A properly cut AI chamber should have a .004"(or so, some like more) crush of the neck/shoulder junction into the same junction in the chamber to establish headspace without relying on the bullet to do anything.

I agree with Heavy, max or near max loads will perform the best to fireform brass.

I always use a max load (for the parent cartridge) of fast burning powder to fireform. Much of the energy is spent expanding the brass to fill the larger Ackley chamber. A light load will result in "Weatherby" shoulders, requiring another fireform to achieve sharp shoulders.

Yup, this is my experience as well. I tried to get out cheap on my first round of fireforming by using low-power loads of slow powder and this is what I got for my effort.

Go for middle-high to nearly highest loads for parent cartridge and you should do great.

What if you got some factory loads?

Say some factory .243 win's going in an Ackley chamber?

Most factory .243 win is loaded plenty hot to make forming very easy.

Thats what I thought...Thx

Using a near max load of 3031 under 225 SGKs loaded about .015"-.020" from lands. Will report back.

This is not your caliber but it is a good illustration of what heppens when you don't follow instructions. This case was fired in my .30-30 AI Contender rifle and you can see this case is about to blow. A complete separation in a Contender would not be very nice. All the cases I used for fire forming had been loaded many times. First no no. Then I took the full power loads out of Ackleys book with IMR 3031 and reduced them by one grain. Second no no. Every one of these cases cracked when I fired them but I was in heavy shade at the range and didn't notice them until the fourth shot. When I sat the fourth case on the bench the head fell completely off. Then I saw the cracks in the others. I read later that an AI cartridge should basically use about 5% more powder than the parent cartridge. I calculated what was listed in Ackley's book and it was much more than 5%. Now I only use new brass and work very carefully. I have been handloading for 25 years and this proves that I can still be a DA with new toy. Thanks guys. Dee

fremont,

I discovered if one uses a full case of powder the neck does not shorten. When a lighter charge is used necks shorten.

I like to load up a bunch and go rabbit hunting. This generates fun practice while fireforming brass.

Worked great. Nice crisp shoulder. Shortened .005"-.010" from standard 35 Whelen case.

Great advice, Blowtorch.