Actually this was for an XP-100 owned by SScoyote here on LRH. He contacted Richard Graves and myself looking to design a handgun system with 1 mile capabilities.
Richard designed the bullet, a 200 gr ULD RBBT and SS and myself talked over the powerplant options and settled at first on the 7mm WSM
Well SS wanted to use Norma brass which is certainly not a bad thing to do when your trying to hit at 1 mile with a handgun. The only problem was that Norma did not make the 7mm WSM brass, only the slightly shorter 270 and 300 WSM
TO use these in the 7mm WSM would require necking up and then back down to form a secondary headspace shoulder for fireforming.
The performance gain would be very little if any so I asked him what he though about using a simple 270 WSM necked up to 7mm? HE said fine and I ordered in some Norma brass to take measurements off and drew up the reamer print and had it made.
When I range tested the XP at 300 yards before shipping it was averageing right at 1.5" groups ctc with a 2-7x Burris handgun scope.
SS has still to develope a load with the 200 gr ULDs so I can not tell you what top velocity potential is. It will be nearly identical to the standard 7mm WSM, within 20 fps I would suspect.
You may want to drop sscoyote a line and I am sure he will get you all the data he has on the wildcat. The nice thing is that you can use a 7mm WSM FL die as a neck die and a 300 WSM FL die as a shoulder bump die so its pretty simple to set up for.
With carbide cutters it is a simple process to take 0.030" off the length of a set of standard 7mm WSM dies as well.