It's not a flint lock - the hammer strikes the firing pin, which strikes the primer. The .45-70 Govt. was a transitional cartridge - one of the first with a brass case and primer, but still using black powder (45 caliber, 70 grains of black powder, hence the name). When smokeless came along people started using that instead, but it can shoot either one. It was the official cartridge of the US military for quite some time. The bullet is slow and moves in an arc, but when it gets there it hits with a THUMP.
If you've never seen it, rent Quigley Down Under. That's the movie that got me hooked on Sharps Rifles.