I had my 300s from the late Alan Bray shop in 1973 [ish], and I was told to always tip it forward after each shot as this relieved strain on the cocking arm system. I didn't always do this and I never noticed any difference in POI, after all the gun is in the same relative position internally whichever way it is cocked. A little while later I had occasion to contact ASI the then importer and I asked the question, with the same reply, it is recommended to tip the muzzle down and re lock the action after each shot, for the same reasons that I was given originally.
Hope this is of some help.
ATVB
abellringer