I forget exactly how you do it. You switch to the mortar as you're going prone or something. This was in v0.2 or something so I'm sure it's fixed by now.
That's because you play a vampire in a house full of zombies who want to eat you. D (The name os a Sega Saturn game...1 letter XD) is a VERY good Survival Horror Game. VERY good, you should look it up sometime, maybe even get it on a ROM