forming cases for a 6.5 Gibbs
 

pretty simple process actually. start with a 270 Winchester.

2nd from left is a 270
3rd is a 270 necked to a crush fit in a 6.5 Gibbs chamber
load it with 11 gr. of unique powder, fill it with cornmeal, plug with a 22 patch packed tight, remove your brake if you have one, keep muzzle pointed down and fire. watch barrel heat cause it will get hot. all the way to the left you will see a fire formed 6.5 Gibbs case, but notice the crack from pushing the shoulder forward. you will lose 2% of the cases in this process. On the right is a 270 and a 6.5 cartridge.
why would you do this? well the straight walls and sharp shoulder of the case lets you shoot higher velocities with less pressure signs, the 6.5 Gibbs will run a 140 gr bullet at 3300 fps, easily besting the 264 win. mag. and use 9 grains less powder doing it.

If I read that correctly, you’re doing a straight neck down to create a false shoulder, and using a cornmeal/CoW fireforming process, yes?

Would you happen to know the case capacity difference between the 6.5-06 AI and the Gibbs? What dies are you using for the Gibbs? I have one of my .30-06’s torn apart right now and have been strongly considering 6.5-06 AI, but I’m thinking the Gibbs looks to have a bit extra case capacity.

yes that's correct, there is a difference of case capacity of around 7 grains of H20, the dies I use are just a 2 die set of 6.5 Gibbs dies, to do it over again I would go 6.5/06 AI, it will still outrun the 264 by 100 fps, and the easiest of the 2 by far to form brass, with the 6.5/06 AI just prime and charge a 25/06 case with a top level load and seat any .264 boatail bullet, and fire, accuracy will be much better with fireform loads in the AI.

I would think that with the correct matching twist rate being available that the 6.5/06 AI,
would be a great choice in a longer range cartridge with comparatively low recoil
that might be a much improved hunting cartridge for game traditionally hunted with a 270 win,
I might just have to consider having a ruger #1 re-barreled as my antelope hunting rifle
rather than the current 257 wby I use.
something in a spitzer boat tail in the 140 grain range ought to provide impressive results