Would larger ASW rounds improve reliability or depth performance?

Would scaling an anti-submarine round up to an 18-inch gun improve its dud rate or survivable depth?

No clear advantage is expected in either respect; purpose-built mortars already fire large anti-submarine bombs without requiring a full 18-inch naval gun.

Purpose-built anti-submarine mortars can already reach roughly 12-inch calibre. Their short barrels and high firing angles avoid some of the difficulties associated with a full-size naval gun. Squid, Limbo, and Swedish mortars are cited as examples of this approach. These are relatively short-range weapons, and their large bombs do not establish a reason to adopt an 18-inch gun tube.