There is velocity loss from shorter barrels but it is not extreme unless we're talking extremely different barrel lengths. The old first edition Lyman Blackpowder Handbook compared various loads from different barrel lengths so just to pick one example, a .50 caliber with a .498" ball of 180 grains weight with 100 grains of 3f powder. From a 26" barrel that load ran 1882 fps. from a 32" barrel the same load went 1978 fps and from a 43" barrel it gave 2095 fps. So the 17" shorter barrel cost only 213 fps. But that is strictly muzzle ballistics. The round ball loses velocity very quickly so that the difference is even less as both loads run downrange. In any case the difference in ballistics would not be noticable in the field but the difference in the guns themselves would be very noticable. Longer barrels are more about style, sight radius and balance and handling properties than actual balistics. I love the slim lines and slick handling of long rifles and fowlers but I don't kid myself with any notion that they are more deadly than a short gun.
