I get what you are saying, but the PIAT was launched by a spring.
It had explosives in it also, it was hoped the explosive discharge of the round would recock the PIAT, sometimes it did sometimes it didn’t.
Common misconception, the PIAT was more like a mortar, with a moving striker. It is believed (i think) that it has no charge, because it could be used inside buildings unlike bazookas etc.
The spring pushed against a 12 lb (5 kg) steel canister and rod that rode up the barrel and struck the rear of the bomb, igniting a small propulsion charge. The heavy bolt and rod, known as the spigot, was used primarily to damp out the recoil of the round leaving the barrel. The charge was also intended to reset the spring, meaning that the weapon had to be cocked only once, by pulling up on the tube while standing on a handle mounted at the rear.
The wiki.