Was playing around at the reloading bench, and put a 8mm bullet into one of my .300 Win Mag cases, and it got me to wondering if anyone had done it. I cant find any data at the normal places. Im guessing performance would be between the .325 WSM and the 8mm Rem Mag.

I have not used that chambering but there is a little trick you can use. Most 8mm bullet weights will have the same weight 30 cal bullet weight. For example, 180 gr 8mm, 180 gr 30 cal or 200 gr 8mm, 200 gr 30 cal. As such, because the bore of the 8mm is larger, it will reduce pressure with same bullet waits so you can simply take a mid level load for a 300 Win Mag with same bullet weight as you are using and work up from there. Say for example you want to use the 200 gr Nolser partions. If I were starting load development for your wildcat with this bullet, I would look up in the Nolser load data for a mid level load using the 200 gr parition in 300 Win Mag. In this instance, Nolser lists a range of 68.5 to 72.5 gr of RL-22 with the 200 gr Partition in the 300 win Mag. I would personally start with around 70.0 grs of Rl-22 under the 200 gr 8mm bullet and work up from there. Again, because the bullet is larger in diameter, the chamber pressure will be less and you can work up from there. Also, another hint when starting load development for a wildcat you are not familiar with, seat the bullets well off the lands and start with a relatively slow burning powder for that case capacity. This will only add to your cushion as far as chamber pressure goes and then you can work up from there and seat your bullets closer to the lands as you get a better idea of the personality of your rifle as far as chamber pressure. Medium loads for the WSM should also work pretty well for a starting load as the WSM has a smaller case capacity then the 8mm-300 Win Mag.

Thanks for the tips ! I have a .325 WSM, but for some strange reason Id like to have one on the .300 Win Mag case. I believe the capacity would be a little better than the WSM also.