The launcher is the smallest pipe bill in the whole mortar setup. It takes one metal pipe, and then every craft of shells takes another, whether you load HE shells or fragmentation shells. Before a Level 3 bench, all of those pipes are loot from barrels, crates and recycled guns.
So plan the research as a set. The mortar blueprint alone gives you a launcher with nothing to fire. Learn it together with the frag shell, which gets the most out of each pipe, and leave HE for later.
Watch out
Don't craft the mortar with your last pipe. A mortar with no shells is high quality metal standing in the yard, and the recycler only hands the pipe back half the time.
If what you want is a hole in a stone wall, the pipes belong in rockets: mortar shells barely scratch buildings.
