1 I think it is possible
2 I have no idea what you would get out of a 338/284 in a 15" barrel
3 At least a 10t but you may need a 8t or 9t
I will have a 338 Lapua IMP the first part of SEP in a handgun. MY goal is to shoot paper out to 1 mile and hunt to a range I feel comfortable with. Here is a Pic of the gun with a diffrent barrel.