I should probably just email ExTank directly, but heck, we should all share.
My knowledge of military technology is pretty much limited to Tom Clancy novels. One thing Tom (he likes it when I call him “Tom”. He also likes “Studmuffin”) has mentioned in several of this books is that practice rounds for tanks are less accurate than warshots. Assuming Mr. Clancy is accurate, what’s the deal? Dammit, we’re Americans - we should be able to fix this.
Sua
Probably the same as factory rounds and re-loads. The accuracy of the measure of explosive, fit of the casing, and the balance, weight and size of the shell. In other words, price.
later, Tom.
We used to use light practice depth charge mortar bombs on board ship and fired them with a reduced charge.
These would probably be more prone to wind deflection.
Not directly to do with the OP but my tuppence worth…
Combination of reduced charge for longer barrel life, and lower tolerances to make 'em cheap.