Has anyone tried this wildcat?

It's not in the books I have so I had to seach for it

www.jarrettrifles.com/cal_243_catbird.htm

What do you intend to shoot with it and at what range?

So basically a 240 Gibbs on 270 brass. - Dan

i beileve that's a Jim Carmichael creation. There was an article on it in PS publications long time ago, but i don't have it.

I am going to use it on fox, ranges up to 400 meters. often in windy condition.

With the selection of relatively high BC bullets
you have from which to choose, oughta work great.
What about barrel life?

with proper handling approx. 1500 rounds so It will not be used for paperpunching.

What velocity will a catbird give the 107 gr bullet from a 26" barrel? The new Sierra reports 3200 fps from a 6mm Ackley Improved.

At some point the law of diminishing returns takes effect on powder capacity increases also.