470Rigby,
My 1916 BSA catalogue reprint (from Skennerton) shows that Metford rifling was still offered in their sporters even then.
Some tips to date BSA Lee Speeds is whether the marking on the receiver strap under the bolt handle is either "BSA Co." or "BSA&M". BSA sold its munitions division ("M" in "BSA&M) in 1896, so any BSA&M rifle is prior to 1897.
Another indicator is the presence of the sliding tang safety ala the earlier Ruger Model 77 rifles. The sliding tang safety on the BSA's carrys a patent date of 1897.
Another tip to date Lee Speeds is to look at the magazine and floorplate. The military model carbine around 1917 or so had a distinctive magazine with an odd attachment on the side up on top. There is a cutout in the side of the floorplate to accomodate that attachment. Having this arrangement would indicate a post-1898 rifle.
Other than that, dating them gets tough.
Concerning the Rigby Lee Speed, Rigby may have been the retailer of a Lee Speed, and would state so on the barrel rib or on top of the round barrel or dustcover as the A&N ones are. I have a Lamb & Adler marked Lee Speed on top of the barrel rib as they were the retailer of this rifle.
These are just my humble observations and I am sure there are more qualified people in this forum with more knowledge of these rifles than I.