UMC Moustache Headstamps


Hello, I have questions about the moustache headstamp on some UMC shotshells.
When were they used and why? Was this a commerative issue, or done for another reason. 1873 seems to be when the A & B series began so it must be after that.
Thankyou in advance for any help.


There is no gauge on headstamp. Probably 1870