Convergence to 200, all guns. Fire at a solid target only at D350 or less. Dont bother with HOs or snapshots, get solid solutions.
The .303s are much maligned, for several reasons.
#1 The vast majority of players experiences are formed by the MA where ac with 20mm or .50 cal batteries are the standard. LAs, 109s, Spits, P-51s, Tiffies...
#2 Most CT setups are 1942-45 and dont have the Hurricane I or Spitfire I to begin with, save the BoB or BoF.
...this leads to the very wrong tactic of firing at "typical" AH gun ranges of D400+, which will yield nothing with .303s, and the mythology begins..."they are BBs"..."they are useless"...ect ect.
Get in close and make it count. Dont get caught low without some backup, you wont escape multiple 110s alone.