Largest gun that will fit on a tank

So I was looking at our glorious Spacebattles logo and noticed the tank barrel on that image is a lot longer than I remember it being on the T-34-85. Which got me thinking, what's the largest gun

Hobby Boss Russian KV 'Big Turret' Tank Vehicle Model Building Kit : Arts, Crafts & Sewing

Tim Mee Dominator BIG TANK for Action Figures 22in long Olive Green – BMC Toys

What's the biggest caliber cannon ever mounted on an armored vehicle like a tank? - Quora

FV4005 - War Thunder Wiki

Largest caliber gun? : r/WorldofTanks

What is the largest caliber gun ever to be fitted onto a tank? - Quora

The Movie Star Ripsaw Mini-Tank Has Reemerged Unmanned And Packing A Big 30mm Cannon

TankHistoria - The FV4005 'Stage 1' was mostly a proof of concept for the L4 gun. The 183 mm L4 was the biggest task-specific anti-tank gun ever built, a record that still

Special Rules – GF9 World of Tanks