Depends on the loads.
The 338-378 is the newest but so far it has already shot a bunch of 1" groups with just throwing it together. No load development. We are still breaking in the barrel. The current load is out of the Barnes book. 108 grains of RL-22 shoots 225 TSX's at 3202fps but the ES is running about 50 fps. It will need some work but still 450 yard testing it is very impressive. I want to try some 225 Accubonds and some other powders in it next. 3300fps should be doable. I don't have a 30-378 but do have a 300wby and 2-257's. My 14 year old wouldn't give mine back till he got his own. The 257's shoot light bullets best so far. I have BD 8-32 on mine and use it for varminting. The 300Wby is shooting 200 grain Accubonds into .6 inch groups at the moment. I'm still working with it. I bought it used but the guy I bought it from said it shot 4” groups at 500 yards for him with TSX’s. The triggers on all of these are adjusted to around 1 to 1-1/2 pounds. Depends on who is going to be shooting it. My 257 is set at 15 ounces. They all are very sweet rifles. I never used to think much of muzzle brakes
but now I wish they all had them. They all are really fun to shoot. We have been doing a lot of 450 yard shooting on water bottles. Next weekend we go out we are moving the targets out to 700 to make it more challenging.