Well since they are shooting nerf howlers, which are relatively light, it would be difficult to get a cannon so large to have significant recoil.mattyzip77 wrote:Instead of making the cannon look like its recoiling hard, why dony you make a cannon that actually does have a badass recoil??? Just sayin>>> :sign7: :sign7:
The first idea that pops in to my head is having the inline cannon on some low friction tracks with a large pneumatic ram; or perhaps two smaller ones. Have some air divert out the barrel in to the ram(s) so that they extend and push the gun back on its tracks. Seems pretty straight forward to me, how well does it suit your design? I imagine there would be some difficulty with timing the air being diverted in to the rams so that it is in sync with the projectile firing. Perhaps you can have an auxiliary tank just for the rams.
The other option is just to have the gun on low friction tracks and see if whatever recoil is present is enough to push it back. I doubt you would get an 88-like recoil from this as the gun would roll back rather than shoot back as with a ram.
Edit: Look up homemade camera dollys for ideas about low-friction tracks.