Sharps used a bullet diameter of .451 in 45. This was supposed to be their nominal groove diameter. However, most barrels were larger than this .464 was very common. 44s with a 446 nominal were often .454, I saw one that was .464!
The problem with GG bullets is that they were largely in the cartridge case and if the chamber was tight they were past expanding by the time they cleared the cartridge case since they "bump up" before they move significantly.
Dr Gunn told me he had all his Grandfathers guns except the "Dutch" gun, Schuetzen, he worked for Sharps and represented them at rifle matches. He told me that one of the 45 2.4" long range rifles had a .464 groove and chamber so tight it would not accept a bullet in the case that was over .451. He said it shot fine with a PP bullet about 1/16" in the case (how the LR ammo was loaded).
No the GG bullets were not fit to the bores since there was too much variation in bore size in almost all the makes until the advent of Smokeless powder. The bullets were swaged and pretty uniform in diameter. But the barrels were all over the place and often the headspace was really large too. Handloaders could get patch paper often referred to as "bank note paper" in various thicknesses to patch the bullets with and this probably helped with accuracy in some guns.
Strangely, or maybe not, many US Trapdoor Springfields military rifles/carbines were over sized as well 460 to 464. These all shot GG bullets that were .457".
Dan