Alrighty, let's see, here's the original...
MK-47: This is a blowback operated rifle using .30 caliber rounds, designed to be an automatic weapon with a similar size and role to the Model 1 Service Rifle. It has a rear pistol grip, a slotted wooden foregrip and a 30 round magazine which mounts on the side. It is based on the Cascade's action, but heavily reinforced to withstand the pressures incurred by full size rifle rounds. The heavy moving bolt significantly affects accuracy when firing automatically, even at medium range. The weapon has a heavy barrel to prevent overheating and help with the recoil, which makes the weapon weigh around 16 pounds, but the recoil from rapidly firing rifle rounds is still a significant issue. Fires 600 rounds per minute. Costs 2 ore.
And the updates:
MK-47A: The MK-47 is reworked around the smaller, shorter .280 caliber intermediate rifle round. This involves a principally identical but shorter receiver and magazine, and the gun sheds weight in general as parts are made with less reinforcement and ballast is removed, down to 12 pounds. A tactical rail is added. The reduction in firepower brings recoil down to acceptable levels, making it a much more practical weapon. It is effective only to medium range, but as it is only capable of automatic fire, it cannot be aimed effectively past medium range anyway. The blowback action still has a relatively heavy bolt, which makes the gun lurch around a bit. It is still moderately cumbersome for close combat.
You have gained the .280 Intermediate cartridge, notably, while the Germans haven't even built the FG42 yet to realize they need intermediate rounds. Do you want to rename the new MK-47A and/or obsolete the original?