HI
To answer your question most of the early guns build in 1910 and 1911 were not cal marked. The three of these are not cal marked. I also have a 7 1/2 inch proto type
built in 1908 it is also not cal marked. There are also some of the first 455 build that are not cal marked. I have one of those also it shipped to Canada in 1910.
I hope this answers your question.
Jim Fisher

Here is serial Number 091 one of 12 Proto types it is not cal Marked also.
It has two Cly one in 44 Special and one in 44 Russian