When Did No.4 Mk 1 production cease at Fazackerly

.....and when did they switch to Mk2 instead. Just wondering really as I have a late 1948 No.4 Mk1 and Im pertty certain I've got an FTR'd No.4 Mk1/2 which was also done in 1948.

There is a large overlap (c.30,000 in the numbering sequence) between Mk1 and Mk2 rifles that occurs in june-july 1949. Although this seems to imply that they finally stopped making Mk1s (at number PF 89,xxx) in July 1949, it would not surprise me at all if a few Mk1s turn up with 1950 dates.

Thank you. Now i have to look for 49 and 50 dates also.