Quote Originally Posted by Col.Colt View Post
This was the first no 4 I have seen with hollowed out bolt . Can I assume the 4 digit serial number begining with "K" indicates production at BSA ?

It would be a correct number for a very early BSA - around 1941/2. All of the later BSA production had the 5 digit number commencing with a "3". If your rifle has a 1944 date, then possibly that was an FTR (factory rebuild) date.

Photos will reveal all!