Krupp made bar stock & the Belgians converted the bar stock into rough bored tubes. The Germans purchased the rough bored tubes and transformed them into barrels. In this case, renown tube finished Wilhelm Kelber finished these. Not really a means to tell as Robert Schüler either had the marks worked off or instructed the mechanics to either hide their initials or leave them off all together. RK would have been the original custodian.

Cheers,

Raimey
rse