I have a Cooper 22 in 243 AI and I finally have my scope, dies, brass, and bullets ready. I am going to use the Hornady 75 grain V-max and from what I've read I need a fast powder for the initial fireform. I'm thinking a near maximum charge of IMR 3031 or IMR 4895 would do the trick. For a full power load I'm looking toward H4350 or Reloader 15. Does anyone have any experience with this cartridge? Any powders others have tried with success?

6mm,

Another approach is to reduce the charge and seat the bullet to the lands. This minimizes case stretch when blowing out the case.

Fireforming the Improved cartridges should be done with a top-end load. In a correctly cut chamber it should not be necessary to jam the bullet since the shoulder will accomplish the same thing. But if you do want to jam, you don't need to reduce the load because the increased chamber size will result in a lower than usual pressure.

Ray

6 Rem I also shoot a Cooper Mod 22 in .243 AI, and found that it is most practical to load 75 V-Max's with a near full load (for a .243 Win) with powders like Varget or IMR 4350 or W760 which will shoot very well for the rifle. I used those on a Pdog hunt and had a pile of 243 AI brass afterwards. I don't like having to shoot the rifle just to make brass, it's wasteful and wears a perfectly good barrel without the rewards. I use 243 Lapua brass and Fed 210M primers and several powders. the first most accurate load was the Sierra 85 BTHP with about 38 grains of IMR 4064, less than .5 MOA for several 5 shot groups. Best groups however come with the Berger 80 gr HP and V V 550. The rifle was a ctually a bit more challenging then I expected to make shoot truly well. But it does now!

In my experience my fireforming loads with the .243 AI produced very little more pressure than the same load in a fireformed case .
The 75gn V Max has quite a short bearing surface and seems in my rifle to accept similar powder charges to the 70gn Nosler BT .
I'd suggest you try a load of around 41 - 42 gns Varget . Think you'll get good accuracy and nicely formed cases as I did . Velocity around 3500 FPS or higher .
In my rifle 43gns is about maximum with Winchester cases . Lapua perhaps half a grain lower .
Interesting that the 80gn Berger Match HP has been the most accurate projectile in my rifle too (but in front of 45.5 gns of H4350).

Thank you all for your responses. I'll try a near maximum charge of Reloader 15. My Hornady manual lists the maximum of 39.3 grains so I'll try 39.0 grains and see how it forms.

No one has suggested this, but I have done this with some of my cases.

12 grains of Bullseye, rest of case filled with corn meal to bottom of neck and sealed with soap.

Do as 308Sako says. You want nice sharp shoulders on the 1st firing and a max load for the parent cartridge is how that is accomplished.
Fireform your cases on critters, you'll be impressed with the accuracy. Fireforming need not be a seperate operation. If you want to use Cream of Wheat try slicing a banana over it.

Stepchild