Time frame for different US manufacturer headstamps

I notice that my W.R.A.CO. headstamps appear earlier product than W.R.A.Co.
Same for R dot P vs R-P. Sorry no dot on my keyboard.
And U M C vs U.M.C.
Do the 2 different headstamps represent different manufacturing periods. Or just different factories or machinery?

I believe F is earlier product that FA - both Frankford Arsenal. Can someone give me the dates of manufacturer for the 2 styles.

Any chance there is a list on the Forum that shows the dates in operation for major US manufacturers?

Thank you,
Jim C

I have yet to notice any pattern in W.R.A.Co. & W.R.A.CO. Or in UMC or U.M.C. both companies used just one plant during this time.

It is most certainly possible their was some manufacturing line to headstamp correlation but box codes did cover the need for it.

If you look in Dan Shuey’s book on WRACo headstamps and their variations you might find answers to a specific headstamp. But I think most of the “O or o” size was just how the bunter happened to be made or who made it.

The R-P & R.P are different times also to the space between & length of the dash or dot, but I’m not aware of any list, not that someone may have one & if they did it would be nice to see as there must be at least 6 variations.

As the the F in FA timing, yes it does seem the F was used earlier as it’s found in as F on the 45-70 Govt. & the .30-40 Krag uses both F & FA headstamps with the FA starting use at 7 02.

1st dated headstamp on the .45-70 is 3 77

Thank you Pete all info