Those Brass framed Cap & Ball revolvers should not be subjected to a full load that is why they suggest a 15 - 20gr. powder charge, the heavier loads will stretch the frame enough to make it useless in a short time "depending on how much you shoot it."
All my replicas are Steel framed Pietta, Navy Arms, & Smith Mountain & will handle a full charge, like mysteel framed Pietta 1860 Armywill handle a loading of 35gr. easily & has had up to 40gr. with no issues in 25 years.
Just use a lighter charge, shoot safely, & have fun.

It does sound like the half cock notch is too long like Lemoyne said but unless you know how do do any gun smithing I'n leave that to some one that does know how.

Interesting that Cabelas would not want the other revolver back.