NOTE I reset my splits almost immediately upon starting the run. The real splits can be found at (https://imgur.com/a/xKCf57F).

Instant Reload Glitch claims another WR. This level isn't quite as easy as L3, since the barbettes have considerably more HP than 15 shots of the fifth weapon (crazy dragon, 15*250 = 3750, barbettes have base 6000). Some use of weapons 3/4 is required on these, unless your units come to back you up in time. I was able to use the splash of crazy dragon on both a boss and barbette, saving ammo and quite some time. Not sure about improvement on this run.