[PeterVerney]

ISTR that harmonisation of our Mosquitos in 1952 was two guns at 350 yards and two at 250 yards. Giving an idealised firing range of 300 yards. Of course in practise, firing at drogues and at ground targets, there was only time for a quick squirt at about 350 yards with the range rapidly decreasing. Bear in mind that firing on the target was not permitted at less than 30 degrees angle off for fear of ricochets hitting the tug.
When we switched to the Meteor NF with wing mounted guns I think similar harmonisation applied. Incidentally I do remember an incident when a wing commander, eager to get a better score, closed to a lower angle off and bounced a shell clean into one of the tugs engines. Ball ammo of course, but made a horrible mess of the engine and as we only had one aircraft modded to tow a flag that put an end to the fun.
In any instance scores were not marvellous and it was not unknown for a pilot to score a blank while over 15% on air to air was considered reasonable and over 30 very good.