If you are picking between the two use your 7.62...bigger diameter bullet, more energy, bigger hole, and quicker dispatch than a 223 hands down. I would STILL tell you use your 308 it’s not like you’re going to go shoot ALL DAY LONG at a big game animals so there’s no reason to worry about the 7.62 being able to shoot all day long comfortably because it’s funner and easier on your shoulder. I know your just waiting for someone to tell you it’s OK and it works well. I still would tell you to use your 308 as it’s designed for big game. The 7.62 was not but it’s your gun and your choice so good luck with your venture. Yes the 7.62 will work as the 223 will but is it either an effective cartridge for deer no, will it kill them sure. If you flinch or if there’s brush and your shot doesn’t hit your Mark perfectly thats where the 308 will prevail...close accounts with more energy and a bigger, heavier bullet. I would tell you to use your 7.62 for practicing all day to get used to using your 308 for once or twice a shot durring deer season. Your deer are going to DRT and be dispatched instantly 99.9% of the time with a bigger bullet and more energy. I’m just one man and one opinion so good luck in whatever you decide. If you flinch or if there’s brush and your shot does not hit its Mark perfectly that 308 will prevail close counts with more energy in a bigger bullet I would tell you to use your 7.62 for practicing all day to get used to using your 308 for once or twice a shot in a season on an animal but will be dispatched instantly 99.9% of the time bullet in more energy just one man one opinion good luck whatever you decide. Lastly I’ve never seen a 7.62 shoot under MOA yet. The round was designed for AK-47s and SKS’s to make it rain with a little bit more knockdown power than a 223 . Most rifles chambered in this round were made for “close counts”...horseshoes and hand grenades not precision shooting. I’m sure their are rifles out there that’ll do it but not many. I would guess a Ruger American bolt might be up to the task but most guns that are chambered in that round or semi automatics and shoot pie plate groups at 50 yards. I know your user name so I’m sure you have a big love for the round so I don’t mean any pun or disrespect but that round just inherently inaccurate unless you build a custom bolt action for the round. If you reload you can download your 308’s to shoot with as little amount of recoil as your 7.62 for practice and I will guarantee it will still be more accurate. I know a lot of people have used the round for children and women who can’t tolerate a lot of recoil and it’s definitely a good starter around to get used to shooting guns or small frame shooter. I tell you to keep having fun and shoot your 7.62, it will help you become a better marksman and you can practice all day long with cheap FMJ ammo for when the count shots are really needed with your bigger rifle. It will help you tolerate and get use to recoil as well the more you shoot. Besides it’s more humane and you owe it to youself and respect to the animal to dispatch it instantly as the bigger caliber will do more way more effectively.