can a full choke be used safely with 00 buckshot
There is no danger in shooting slugs or buckshot in a full choke.
However, as has been pointed out, you may very likely get better buckshot patterns with a more open choke.
2 3/4" shells have way less range than 3" 00 buckshot shells?
Way less Max range? No, certainly not Way less.
It all depends on how you gun patterns each shell length.
In some guns, it may be 10 yards more. In others it might be the same distance.
Buy a pack of paper dinner plates and go test some loads and chokes.
Whatever range the load/choke combination will keep all 9 or 12 pellets inside the paper plate is the max effective range for deer.
But I agree, Forster type rifled slugs in a smooth-bore barrel will increase that range maybe twofold over buckshot. It should be no big trick to keep all the slugs on a paper plate at 60+ yards.
I will also caution you that 3" Mag buckshot will quickly have you flinching so bad from the recoil you could easily miss a deer entirely!
Most folks will shoot far better with 2 3/4" loads.
rc