I’m sure there was some variation of procedures but your proposed procedure makes sense. Undoubtedly, it was a heated vat of Cosmoline or the Soviet, Chinese, etc. equivalent of the high melting point hydrocarbon mixture. Dipped and then hung to drain and cool.
I’m sure they all had OSHA approved PPE in a well ventilated environment to keep from breathing all the vapors or absorbing it through their skin
If the workshop wasn't complying with all known safety regs, I'm sure the workers just complained to the union foreman or put a note in the suggestion box!
That process seemed plausible, but I'm just guessing.
I've have cleaned a couple that had the barrel full of the stuff. What came out appeared similar to a long pencil. Perhaps they had a temporary muzzle cover to help retain the cosmoline until it solidified?
Others didn't have that much in the barrel, so there may have been different processes or it changed over time. Maybe each person had their own way of doing their batch of rifles...?
The rifle I recently did had
none in the rear receiver area below the main spring. That made me think it was only partially dipped and then smothered on the outside by hand.