Airsoft Mortars.
Three main types. Static, safe and dangerous.
Fields will sometimes have deactivated or home built airsoft mortars. They don’t do much aside from being an objective to capture in the game. Home built versions are commonly made of PVC and can look quite realistic.
The difference between safe and unsafe all depends on the construction of the materials of the launcher and the projectile. Most mortars are home made with some people making great looking and functioning ones , they fly far, “explode” on contact, however get one in the head and you will be visiting the Emergency ward. PVC pipe is the most common construction material, for a static display this is fine however, I will advise against using it for the launcher. Copper or steel pipe is much stronger and are much more durable. Caution on the projectile itself. A heavy bomb will fly more accurately but there is much more danger to the other players. See the video below.
A review of a commercially available airsoft mortar airsoft mortar. by FuzzyDicePimp has a good review of the device. Though this is called an airsoft mortar it look like an item that is for range use only, the projectile is quite heavy and and Mr pimp mentions the amount the bomb imbeds into the ground should be an indicator that it is a less than safe for game use.
A safety note. Keep your hands clear of the muzzle of the launcher when you drop a bomb down the tube. When the projectile is exiting the tube any fins can cause quite the injury. On a real mortar it can cut off a hand. Seriously, Knew a guy who had to escort a recruit to the hospital with half of the other guys hand wrapped in a rag. Thankfully airsoft mortars are much safer however i still wouldn’t want to be looking down the tube when it goes off.
When working the mortar its best used as a team, one guy aiming one firing, will increase accuracy and rate of fire. Make sure the legs are spread wide, on solid ground and as level as possible for best accuracy.
Also here is directions on how to build your own airsoft mortar, It uses PVC so use at your own risk and discretion.
Here is a hell of a good airsoft mortar. Constructed of steel and looks durable. The only concern on the safety of the rounds, they look like pyrotechnic and heavy.