Futile no doubt, but what the heck. Wildcatters are notorious for their wild velocity claims and it is inevitably because, in the absence of load tables proven with pressure testing equipment, they just "load her up till pressure signs occur". Hardly foolproof, as the "classic" pressure signs can be very deceptive.
A solid, proven rule of thumb is that for every 4% increase in case capacity, you will see about a 1% increase in MV at the same pressure. The 35 Whelen Imp is about 6% larger in capacity than the unimproved version (not the best candidate for the modification), so you should be seeing about an extra 1.5% increase in MV. A 5% increase is clearly due to operating at higher pressures, not the effect of the small increase in capacity. Best of luck.
I get 2550 fps out of a 24" barrel running 60.0 grs of RL15 over a CCI Magnum primer. This is 0.5 grs over the published Alliant max, and I do so because I have a long throat and can seat the bullet way out at 3.420". Even then, I doubt I could get more than another 3.0 grs of powder in the case, but since my pet load is 58.0 grs it doesn't really matter. I'm confident I could get 2800 fps with a faster powder at a good 70,000 psi and likely be ok. I just don't want to.
Barrels vary, as do chambers, so too will the MV various guns will produce with the same powder charge and bullet. If you are getting much more than 2600 fps with a 35 Whelen and 2650 fps with the Improved version, you might not be unsafe, but you certainly are running over spec pressure.
