Help with fireforming a wildcat

[bigd 7378]

Hello fellas. I have a 7mm wildcat on a 300 WSM case. I need help with COW fireforming, I neck down 300 WSM to .314 neck diameter in two steps. It's a tight crush fit in my chamber. I have no issue using Winchester, Hornady or Norma 300 WSM brass. After fireforming I use a bent paper clip to check for case head separation and no issue. As soon as I use Bertram 300 WSM I get severe case head seperation. The pictures show my necked down 300 WSM brass on the left the neck 3 cases are Bertram. The next cases are Winchester, Hornady and last Norma.
All these were done today using exact same die set up and loads. I have used Winchester and Norma brass the last couple years and no issue. Now I want to fireforming some more brass since the corona thing and I'm having issues.
What do you guys think is going on? Any help would be appreciated!!

 

[can1010]

Bertram brass is pretty hard brass and don't take well to that type of forming without annealing first. it also usually has less case capacity and will require a lower charge to form.
I would anneal first and use a lower charge and fireform in two firings with annealing also between firings

 

[Doublezranch]

Bertram brass is too hard even with annealing. Bertram brass is an excellent option for non wildcat chambers. It's very strong and durable. That being said, it doesn't except change very well. I have tried it on a couple of wildcats in hopes that I could get it to work. Unfortunately the alloys they mix with the brass are too strong to allow drastic change in form.

 

[bigd 7378]

Believe it or not the 300 Bertram brass i have is the lightest by far and has the most case capacity by quite a bit. I thought the same thing that it was gonna be the heaviest and least capacity. I will try annealing the brass first and see what comes of it. If no go still I'll resort back to Winchester and Norma

 

[fguffey]

It's a tight crush fit in my chamber.

I have never loaded for a chamber before determining the length of the chamber from the shoulder/datum to the bolt face. The only advantage I can gain by measuring the length of the chamber is a tight fit between the case and chamber. My opinion, there must be something going on that we do not understand.

Necked down: Are you assuming the crush fit is caused by a long case (from the datum to the case head) in a short chamber; point, case head separation does not happen with a crush fit. There are methods and or techniques that are not practiced by reloaders when determining what happens to the case when fired. I have one rifle with .016" clearance between the shoulder of the chamber and shoulder of the case when fired; never a case head separation.

I have fired 8MM57 ammo in two of my 8MM06 rifles, that is .127" clearance between the case shoulder and shoulder of the chamber. No case head separation; to understand what happens to those cases is to understand where the neck does when fired.

I did have trouble with a model 70 Winchester with a 300 Win Mag chamber (very long story). The rifle got back to Winchester, they had it for a long time etc etc. and then they returned the rifle in a new box. I thought my ammo chambered with difficulty, the problem was just the opposite. They returned the rifle 14 years ago, I have yet to take it to the range.

F. Guffey