Primarily in the uk there is little to no use for 'scenario weapons' such as mortars, grenade launchers and RPGs
In uk scenarios we don't use things such as the 'tanks' and 'demolition' characters
(In tfd scenarios we have used demolition squads but ours are different *)
In the us certain scenarios use nerf rockets or special paint colours to eliminate tanks or to count as destroying a bunker or building
* in tfd we like things that go bang and/or make smoke, accompany that with our sponsorship arrangements and our technical guys building gadgets we can put working props into the hands of players. This also brings in safety issues and we have to manage what pyro is used and how it is used
Nerf rockets may seem like a nice little soft toy, but there are risks that go with them. When these are used in the us they are accompanied by rules and often literally a accompanied by Marshall's to observe the rules and safety (Marshall's either accompany the rpg/mortar teams and/or the tank/bunkers)
There are commercial launchers, and there are plans and guides on how to make them. These could be spring loaded but are more often full on compressed air versions of potato guns. You could damage yourself building one
In addition to nerf rockets they have been built for (and even if not designed for) firing smoke grenades or flashbangs
These are particularly risky - they are launched with more power then a throw, (consider being smacked in the mask with a launched smoke grenade) and in the case of a flashbang come with the risk of detonating in the launcher
There have been cases of using commercials produced launchers for smoke at British scenarios - but only by trusted users in specified circumstances
If you safely built one you could present it to a site owner / event organiser and see what they think of it. They may put it into the scenario, but in general play there is no real use in them
