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

The americans may have a big gun but we have the biggest gun : r/tanks

South Korea to hold largest defence show in bid to boost global sales

WOTB THE LARGEST GUN!

What tank has or had the largest gun? - Quora

Tank Archives: Big Gun for a Big KV

What tank has or had the largest gun? - Quora

155mm Gun Tank T58 - The Biggest Iron - Ground - War Thunder — official forum

How Nazi Germany Created the Biggest Tank of World War II

French Char 2C: The 'Berry' Big Tank of WW1

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

Tim Mee Dominator Big Tank for Action Figures - 22in Olive Green - Made in USA : Toys & Games

Schwerer Gustav - Wikipedia