Thanks for the response guys! I checked at the Gun shop where I am supposed to pick it up and was told I cant substitute so If I want to go to something a bit less monstrous, I'll have to take a little beating or sell it outright and buy something else. Right now, I hunt deer with a Marlin 30-30 thats like an old friend. had it since I was 14 and have killed dozens of deer with it. I have a ruger .270 thats an excellent shooter but own nothing more powerful than that. Sounds like the 340 may be more than I have use for until I go for a Grizz or go to Africa. Gotta decide whether to swap it in on something saner like a 300 Win Mag or 300 WBY Mag.
In the meantime, I think I'll resist the urge to fire it till I decide.

If I keep it, I'll definitely handload for it. I see loading data for bullets down to 185 Grain but wonder how that will perform.

Anyway, thanks for all the input