太深奥了

欢迎入吧

其实我也在想这个问题，我跟楼主有同样的疑问

被解放的姜戈里有那么个镜头，开枪的时候铜弹壳洒一地，而那还只是1858年的背景，我当时就怀疑

最后我认定整个美利坚内战时代都只有子弹和火药分离的左轮手枪，铜弹壳是战后才发明或应用的，1868年背景的八恶人有可能使用

好问题

考虑到八恶人里有一首歌是1906年穿越回去的，铜弹壳应该也是同理

后期子弹进步是在普鲁士。德国观察团在观摩美国南北战争中受到启发，发明了今天使用的步枪子弹

In the American Civil War (1861–65) a breech-loading rifle, the Sharps, was introduced and produced in large numbers. It could be loaded with either a ball or a paper cartridge. After that war many were converted to the use of metal cartridges. The development by Smith & Wesson (amongst many others) of revolver handguns that used metal cartridges helped to establish cartridge firearms as the standard in the USA by the 1870s although many continue to use percussion revolvers well after that.
In the United States, in 1857, the Flobert cartridge inspired the .22 Short (another rimfire), especially conceived for the first American revolver using rimfire cartridges, the Smith & Wesson Model 1. A year before, in 1856, the LeMat was the first American (French-designed) breech-loading revolver, but it used pinfire cartridges, not rimfire. Formerly, an employee of the Colt's Patent Firearms Manufacturing Company, Rollin White, had been the first in America to conceive the idea of having the revolver cylinder bored through to accept metallic cartridges (circa 1852), with the first in the world to use bored-through cylinders probably having been Lefaucheux in 1845, who invented a pepperbox-revolver loaded from the rear using bored-through cylinders.[23] However, Samuel Coltrefused this innovation. White left Colt, went to Smith & Wesson to rent a licence for his patent, and this is how the S&W Model 1 saw light of day in 1857. The patent didn't definitely expire until 1870, allowing Smith & Wesson competitors to design and commercialise their own revolving breech-loaders using metallic cartridges. Famous models of that time are the Colts Open Top (1871-1872) and Single Action Army "Peacemaker" (1873). But in rifles, the lever-action mechanism patents were not obstructed by Rollin White's patent infringement because White only held a patent concerning drilled cylinders and revolving mechanisms. Thus, larger caliber rimfire cartridges were soon introduced after 1857, when the Smith & Wesson .22 Short ammunition was introduced for the first time. Some of these rifle cartridges were used in the American Civil War, including the .44 Henry and 56-56 Spencer (both in 1860). However, the large rimfire cartridges were soon replaced by centerfire cartridges, which could safely handle higher pressures.
英文维基Cartridge

还是要看枪的种类，比如著名的柯尔特海军左轮，就是分装弹。而柯尔特单动左轮就是一体弹了。考虑到南北战争的时间。个人认为还是使用分装弹的手枪占大多数。

至于子弹外形。要知道分装弹手枪的装填简直丧病，我还是拿柯尔特海军左轮举例子。首先，要把击锤扳到保险位置（就是正常能扳开的最大位置的二分之一）然后用火药壶向弹巢里倒火药，在依次装进去垫片和铅弹，接着在弹巢尾部依次装好火帽。你以为这就结束了？不！还要用枪管下方的通条挨个弹巢的压实，最后把击锤放下来。这才算装填完毕！而一体弹可用不着这么麻烦。

至于这两种之间的分水岭，则是南北战争过后的西进时代。具体年代我不确定，但是大致就在1870年到1880年之间。比如说著名的柯尔特单动左轮（就是你说的一体弹）发明就在1873年。