Rich Pierce...I guess you’re asking about kit guns, not actual originals. One unintended outcome of standardized kits is folks start thinking that they represent the majority of originals they purport to be based on.
The weight of a rifle is usually barrel weight plus 3 and a half pounds. It can be more if for example the buttplate casting is heavy, it has a thick cast patchbox, etc. Overall weight can be barrel weight plus 3 pounds or slightly less if using sheet metal buttplate, guard, no box, the wood is not dense, and so on.
The balance of a rifle is mostly determined by the balance point of the barrel. A straight barrel 42” long will balance about 20” from the breech because the tang adds mass. A swamped barrel will balance closer to the breech by an inch or so. A shorter straight barrel balances at the halfway point also more or less.
The current “Isaac Haines” and “Marshall rifle” kits benefit from somewhat shorter barrels; often 38”.
With any 2 barrels of identical exterior dimensions, the bigger bore barrel will weigh less.
Thanks so much, Rich. I wish there were more simple explanations like this available. Testimony to a forum...