I know that some 7-shot carbine rifles were used during the war, but that was only a select few. What if these weapons became a standard in the army?
What effects would this have caused?
What effects would this have caused?
Repeating or semiautomatic?
Repeating rifles would have been just about doable for the US forces from about '63. The USA developed a huge arms industry in record time, with some very modern designs and massive capital inflows. By the end of the war, cavalry and many infantry units had repeating or breechloading guns. The Confederates hated it, and many people in the general staff were opposed because they feared it would overtax supplies.
Semiautomatic, I think, is ASB.
Google "Revolving Rifle". There had been experiments with these in the Civil War and they were very successful. I don't know if those count as Semi-Automatic, but what the heck.
They were not "very successful" either The only revolving rifle to see any substantial service in the Civil War was the Colt Revolving Rifle, and it was generally regarded as a very flawed weapon. It was slow to load (the same as loading a cap and ball revolver pistol) and the cylinders had a nasty habit of all going off at once in a chain reaction, taking off the hand of the person holding the rifle. In general, they were pieces of crap.
Wikipedia:Colt Revolving Rifle said:The weapon performed superbly in combat, seeing action with the 21st Ohio Volunteer Infantry Union forces at Snodgrass Hill and at the Battle of Chickamauga during the American Civil War [3]. The volume of fire from this weapon proved to be so useful at both battles that the Confederate forces were convinced that they were attacking an entire division, not just a single regiment. In total 4,712 were purchased during the Civil War [1]. Despite these victories of the weapon, the rifle's faults would prove fatal for the weapon. A board of officers met, and after evaluating the evidence, it decided to discontinue the use of the weapon. The weapons were sold for 42 cents a rifle, a fraction of the original purchase cost.[2]
Your best bet would probably be a breechloading rifle, or maybe an earlier developed version of the needle gun. I always thought it would be interesting to have a scenario where both sides have the latter . . .
Do you really need an earlier invention? The Dreyse needle gun was invented in the 1830s, a decade before the muzzle loading Minie rifles. The Hall rifle was produced in 1819, the Kammerlader in 1842. These are just a few of the several breech loading designs around before the ACW. It took that war and the Austro-Prussian War of 1866 to finally convince armies the age of muzzle loaders was over.