Hi Flint,
BSA resumed air rifle production after the Great War in 1919. They offer two new models of "The BSA Standard Air Rifle". The very first rifles to be produced used up some stocks of pre-war parts, so often dont totally conform to the spec of the new rifles, but once these parts were used up, then they went over to fully spec'd productions as follows
BSA Standard Air Rifle No1 Bore - this was a short cylinder, 39" long gun in .177 cal. ( it had an L prefix to the serial number on the trigger block)
BSA Standard Air Rifle No2 Bore - this was a 45", long cylinder, heavier gun in .22 cal ( it has an S prefix on the serial number on the trigger block)
( Dont forget trigger blocks are fully interchangable between guns - leading to mix ups (ie S prefix to the serial number, but gun is in .177 cal etc etc)
In 1921/22 BSA introduced a long cylinder 45" gun in .177 cal, designed for target shooting (as shooters wanted something heavier than the standard L prefix guns). These guns have a CS prefix to the serial number, and are generally known as "Club Standards"
The L prefix guns are commonly known as Light or Ladies Pattern guns ( this stems from Lincoln Jeffries, inventing the smaller, lighter size for use by Youths and Ladies, and marketing it as such in his adverts of the time)
Here is a thread I started a while back, which details all the .177 models which were produced by LJ and BSA ( if you are the kind of collector who wants to find EVERY model type out there) Good luck with your search
http://www.airgunbbs.com/showthread....uot-Collection