Lincoln wanted a victory yes, but I really think he was saavy enough to know that emancipation was by far his best and ultimate weapon against European intervention. I have no doubt that US ambassadors to France and Britain knew of it and were prepared to drop that nugget if it became necessary.
The cartridge concept you speak of was used for several designs during the war but it was difficult to keep spent caps from jamming the machanism of the guns in which it was tried.
A far more successful concept was the Requa Battery Gun, but it was really artillery. The few times it was used it proved to be successful with a decent rate of fire but like other guns of the time quickly overheated and couldnt maintain the rate of fire.
By far the most successful multi round gun of the war was the Napoleon smoothbore firing cannister or grape. It had better range than any smallarm and the large balls, about an inch in diameter, were lethal as hell over a mile or so. But, again, artillery.
One historian I read many years ago supposed that upwards of 90% of the casualties during Picketts charge were due to cannister and, starting at about 700 yards, double cannister.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.