Go take a look at howitzers and you will see that they traditionally have shorter barrels, due to the lack of a need for higher pressures and longer ranges. Howitzers bring the big bore to short range combat / demolition. Historically, they were not very effective against AFVs due to their inaccuracy and low muzzle velocity. Did just great against their intended targets - buildings and infantry (especially with the anti-personnel high explosive rounds).
This one looks like a long-range gun, an artillery piece. No one saw an issue with it over at CGL? Otherwise, I have no quibble and would love to commission a piece for my fan-made TRO [[link]
However... it's nearly finished.