Hello and happy new year to all. Will an original AK74 muzzle break perform the same, rapid firing on an AK74 clone, as an aftermarket (US made type) that works for 7.62x39 or 5.45x39?
This depends entirely on what kind of American AK-74 brake.
There are "look-alike" brakes like the Tapco type, and there are very close copies of the original.
The Tapco types offer at least some braking action but since they aren't constructed anything like the real AK brake, they offer little real reduction.
The better American made exact copies work just as well as the original Soviet AK-74 brake.
Also, to get the most effect out of an American exact copy brake on a 5.45x39, it has to be a 5.45x39, not a 7.62x39.
The larger hole in the 7.62 allows too much gas bypass in the 5.45.