I once owned a beautiful example of this maker's guns. When determining the origin I discovered a mystery that I never sorted out.
This nineteenth century firm seems to have two sites. One in Liege and one in London. I could not determine if the gun was built in Liege and finished in London or was completely built in England. Finally decided that it did not make much difference as it was wonderfully executed and worthy of either city's best.
Seems that this was a family business where one branch was working/selling in Belgium and another working/selling in London.
I don't hear of many Masu guns and think that their Masu marked pieces are few.
Unless corrected, I think that none would be other than black powder proofed. This would make little difference if shooting with 6000/7000 PSI lead loads.
Hope that this helps.
Best,
John
