As a bit of interest, BSA had a zillion of these sights in stock when they closed and half a zillion were acquired by P-H......where they languished unsold and unwanted until one day.................. P-H got the contract to supply a bastardised, unloved and really unwanted Mauser bodies target rifle to the UKCadet Forces in place of their old No4 target rifles. The procurement chaps had forgotten the mnemonic KISS for Keep It Simple Stupid that day and instead of just re-issuing them with L39's that a) they surreptitiously acquired from their local TA units and b) they were already using in the Cadet competitions and c) were a x10 cheaper option, they went full steam ahead and ordered the P-H L81 target rifle. Alas......., the order didn't include competition sights. So back to the drawing board. They came up with a backsight that consisted of a converted No5 backsight. Yes....., I know that the calibrations didn't match the L81 bore, m/v or, well....., anything really. You couldn't make it up. People sat there, open mouthed, including me who used to beg and borrow the occasional No4* or L39 to use in comps. But they did. The end result was that it was doubly useless but worse, the Cadet Forces had to then purchase brand new, purpose made competition sights. And just GUESS where they had to buy these new and VERY expensive comp sights from.........? Yep....... P-H!
That's why there is a glut of No5 sights....... Another useless bit of history
*My sons school used scopeless No4T's as their target rifles, purchased cheaply in the 50's, fitted with spaced P-H 5C sights