Agreed. Several brands of artillery would benefit from new barrels-although resin could be just as effective and possibly more cost effective as turned barrels. That said, in some sets it would be just as well to replace the whole gun-barrel and carriage. And then there are the limbers and caissons. It's pretty frustrating as there are some pretty nice figures for artillery out there that are let down by their guns(and, of course, the guns from certain eras would benefit from PE shields). And all guns would benefit from being cast in hard plastic.
Years ago I was pleased to hear that HAT was going to include some extra parts in some of their figure sets such as muskets, swords, flags, etc. The resulting pieces weren't as good as I hoped for and I found myself wishing for hard plastic accessory sets such as you can find for 1/35 figures.