You speak slightingly of the Projector, infantry, anti-tank (PIAT for short). Also known as a Spigot mortar. This was basically a tube with a spring loaded rod in it, and a shoulder piece at one end. (mind you, you did not want to place it against your shoulder when you shot it). You compressed the spring (if you were charles atlas) put the bomb in until it rested against the rod, made sure that you did no lower the barrel too far, because the projectile would slide back out, pointed it in the general direction of the enemy, and set the thing off. This sent the bomb in the general direction of the target at a somewhat leasurely pace. All you needed now was 3 minutes and a block and tackle to reload because you probably missed.
The disadvantages of this weapon (?) are pretty clear. Short range, slow reload, inaccurate, and needing a lot of physical strength (though it is not in itself very heavy), to say nothing of the projectile falling out of the barrel if you pointed it down.
It did have a couple of advantages...
No backblast - you can fire it inside a building and not have a problem, also the firer was much harder to spot.
Unpowered projectile meant that the the bomb followed a ballistic course.This meant that you could use it for indirect fire, and it was used that way. It was also used to attack the deck armour of AFVs in this manner.