I would just check around and see what you can find, run a few different rounds through it and find what it shoots best. For the future, check out this ammo www.garrettcartridges.com This stuff is loaded hot and is pretty fun to shoot. For whitetail deer, most .44 mag cartridges will do the job, just place a nice shot right in the boiler room and you will be set. Also, the .44 mags are very efficient for people who reload to shoot, but if you buy boxes at the store it is pretty costly. So if you can, reload or find someone who reloads and maybe buy them the gear they will need to do it. That is going to be a sweet gun, real looker too. Good luck keep us informed.