Just to roll back to my earlier comments...
I should say that the difference in power between my Chinese and Romanian ammo could easily be "batch issues" - basically, you're going to get differences from one batch to another, regardless of where it comes from (China, Russia, Bulgaria, Czech, etc.)
54R has a pretty wide tolerance/spec to start with, and that spec has been , as far as I can tell, a bit of a moving target over the years. Different bullet weights/powder charges, lacquered, un-lacquered, copper-washed, etc., some were specifically made "hotter" for use in aircraft MG's (303 British had different loads for aircraft MG's as well).
You can spend a lot of time deciphering production codes to try and figure out exactly what you're getting, or...
Do what I choose to do. Buy the best crate deal available at the time. Open up a can, go through 20-50 rounds figuring out where it's hitting, adjust accordingly, then work your way through the rest of the crate. When you're about halfway through a crate, buy another so you have it on standby for when you finish burning off the first crate.
Oh, and that SMELL from popping open a sealed can... Yummy, I love the smell of the rotting corpse of communism in the morning.