You still haven't put a picture of the rifle up. I'd like to see it. Also, since you posted on it, you haven't updated on what you found out from the gunsmith. One way to check headspace on the rifle so you'll know if it is an improved or a Brown-Whelen is to smoke the standard Whelen cartridge or a 30-06 cartridge with a candle and chamber it. If you chamber it and it is tight when you do, or if it has a ring at the front of the shoulder near the shoulder-neck junction where the soot is worn off by chambering the round, the headspace is correct for the Ackley Improved, and its safe to fire standard .35 cartridges in. You will want to handload for this round, and when you have some Improved brass, you can go around 4 to 5% over max on your loads if you work up carefully. The Whelen round with bullets of 225gr to 275-300gr. will hammer anything including really big Brown Bear. If your barrel twist is 1 in 14, it will stabilize 300-310gr. bullets. 1 in 16 will stabilize up to 270-280gr. and maybe 300gr. bullets. Check out Whelen's Northwoods Trails on the internet and you will find a lot of useful info on handloading and pressure tests. He has done extensive testing of both loads and bullets in the Whelen.