The Lee-Enfield Grenade Launcher Can Launch Alternative Projectiles.

There is a grenade launcher attachment for the Lee-Enfield rifle (.303 British) that can be used to launch alternative projectiles, like tennis balls.

The cup design of the Enfield launcher offers a more flexible assortment of projectiles as compared to the spigot design of the M1 launcher. Whatever you can stuff into the Enfield launcher can be a projectile.

In the following video, Brandon Herrera demonstrates this flexibility.