Quote History Quoted:
A demil tube can fire a trainer rocket because the trainer is shorter than a live rocket. I wanted one to let people shoot tannerite with.
View Quote
Not really. Most demil'd RPG7s have a rod welded through the firing pin hole. You need a firing pin to shoot it. Some of the subcal rifles have a removable fake 'launch motor', and some don't. If you have one with a removable launch motor, and if your launcher is pinned behind the firing pin, then yes, you can use the subcal adapter. Not many RPGs are demil'd like that.
Also, the rifling on the adapters (at least the ones that I have seen) is super deep. The purpose of this is to vent propellent gas from a standard round past the bullet, so the bullet has lower velocity and ballisticly matches the trajectory of an RPG projectile. With the reduced velocity, I would not be confident that it would initiate the tannerite.