Always learning on the forum !!

Many thanks to Keith aka Rockdoc.

Source: 13pdr Shell Identification

On 21/02/2011 at 02:49, Rockdoc said:

The 13pdr 9cwt round was for AA work. The gun it fitted was the sleeved-down 18pdr that retained the 18pdr breech, allowing the 13pdr shell to be driven by the charge for an 18pdr. This increased the muzzle velocity from about 1,600 ft/s of the 13pdr 6cwt (i.e. the RHA gun) to about 2,100 ft/s. The case should be swaged down like the RH example in John's photo.

Keith

Wkikipedia QF 13 pounder 9 cwt

Very clever idea, though must have been a Quartermasters nightmare with Ordnance phoning him up "there appears to be a problem with your ammunition indent, you have ordered 13 pounder shells which are for a RHA gun, 18 pounder cartridges which are for a RFA gun, and you are a Quartermaster in the RGA".

No wonder everyone is looking a little bemused: