Hello guys!

Is there a 30. cal. wildcat out there that has greater velocity than the .300 win. mag. BUT can still safely chamber and fire a .300 win. mag in a pinch (lost, stolen or airline problem ammo)?

Looking for a backup cartridge that might be more widely available worldwide should the worst case scenario happen and have none of my ammo to hunt with.

300 win mag Ackley improved.

Sure but I was told that this might only give about 3-4 grains more powder and about 30fps. Sound about right?

I was looking for a wildcat (longer or fatter or whatever) that would give me about 100-200fps more but still allow safe chamber of a 300 win mag.

Don't know if such a beast exists but will try to hunt one down??!

You could build a 300 Wby, and fired 300 Win ammo in it.

If I were going to build a .30 caliber wildcat with more power than a .300 Winchester, I think I would use the 8mm RM case necked down (which is also very similar to the .300 Jarrett). While I wouldn't necessarily recommend firing a .300 Winchester factory cartridge in such a chamber, if the chamber were made to appropriate minimum dimensions (as you would expect a custom chamber to be), then the .300 Winchester case neck would extend into the chamber's neck, the case would be headspaced on the belt, and presumably the cartridge could be fired without dangerous results.

I've seem 300Wmag cases that were shot in 300Wby all the time. Since the headspace is on the rim it would be no different than fireforming. Don't have a clue as to the accuracy.

Accuracy isn't good at all, it seems.
See the start of this thread over on Medium Bores: thread

Well, a .300 Weatherby is an "improved" .300 H&H, so it should be able to handle the .300 H&H OK. Haven't tried it in mine, but Roy Weatherby originally made his .300 Wby cases by fireforming .300 H&H.