I would put that rifle later than 1928. It has the final pattern stock with the angular pistol grip configuration, combined with the BSA letters raised in the checkering. This stock didnt come into manufacture until the early 1930's.
The serial numbers on these later BSA's were not related very closely to dispatch dates or indeed production periods so it is sometimes the case that consecutive serial numbers could have left the factory up to three years apart
Most of the books claim that it IS possible to precisely date all standards using the serial number. This is not the case with the later production guns.
The only way to precisely date the guns is to refer to the remaining surviving sales legers, and John Knibbs has those.
Lakey