This a fairly obscure wildcat. I have never seen any published loading data for it. If you look at familes of cartridges based on a common case; the empirical trend is that as the bore size goes up, you can load a little more powder at the same bullet weight. For instance, look at the data for the .270 Win. with a 150 grain bullet and compare it to the 30/06 with a 150 grain bullet - both calibers using IMR 4350. Or the 7MM-08 and .308 Win. with both using 150 grain bullets andIMR 4064.

With that in mind, and if I couldn't find any data, I would look at the .340 Wby loading data for the heavier bullets. I think there are 250 grain bullets for both the .338 and .358. Try a .340 Wby starting load for the .35-340 with a 250 grain bullet, and then work up from there.

Also, with any non-standard chamber, determine the neck diameter of the chamber and compare that with the neck diameter of a loaded round. You need at least .003 to .004 of clearance. .005 to .006 would be even better for a hunting rifle.

At least, that's what I would do in the same circumstance. Of course, there is a risk that a whole gang of Murphy's could come to focus on thislogical processand cause your gun to blow up. In which case, I do not want to hear from Norton Frickey on your behalf . . .