I'm just browsing Wikipedia, and the article on the Australian QF 25-pounder short mentions that both British and Australian variants of the 25-pounder were capable of firing "propaganda" shells. The wiki sources this claim to Peters et al.; The Oxford Companion to Australian Military History.
I've never heard of artillery being used for such purposes, but I'm assuming we're talking about some kind of leaflet dispenser here? Were these really developed and issued to regular artillery units? Were they ever deployed, and how would they have been used in practice?
They are briefly mentioned in the Official History by General ISO Playfair as being utilised in the Tunisian Campaign, and fired onto Axis positions to reduce enemy morale, often in conjunction with more conventional leaflet drops from aircraft, and were also utilised during the campaign in North-West Europe.
To achieve this, Allied forces converted their base-ejection smoke shells - which usually expelled smoke canisters - into carrying canisters of propaganda leaflets, although these were somewhat unreliable due to the propellant charge potentially igniting the leaflets, as well as the rigours of impact on printed matter. The Germans on the other hand, developed a specialised 105mm shell for the delivery of their own propaganda, the Weiss-Rot Geschoss, utilising a split tube that would fragment in mid-air and scatter the leaflets.
Playfair, History of the Second World War, IV: The Mediterranean and Middle East: The Destruction of the Axis Forces in Africa, (HMSO, 1966)
Hogg, Ian, German Artillery of World War Two, (Frontline, 2013)