SPG Stun, or lack thereof

Draschel: The earliest examples of stun, are Bison and stock gun on Grille and SU5. They have 150mm howitzer, but it is hard to use them because of short range. The only artillery gun with less than 150mm yet still has  stun capability, is Crusader SPG, which has 139mm  (5.5in QF) gun that can stun. All other artillery cannons need 150mm bore size for their stuns. When using artillery, stun is only delivered with primary HE that deals the high radius effect. Alternate HE rounds, with more pen and flatter flight, will not stun but cause more damage and have more penetration. The earliest practical artillery cannons for stun include top gun on Grille, SU122A, M41. I think Tier 6 is even better, as SU8 , AMXF3, M44 are nice for their tier.