I've made this because though Jake's shell catch for the goblin was a cool innovation, I've had very mixed results when it comes to the shells sealing with the muzzle. I had the same issues with this silly-booster. I've found the ejector for the silly pilot to be more reliable and unlike the goblin this model has the space for it.
I'm pretty happy with it at this point so I'm putting it here, though the geometry is kind scuffed.
Assembly is pretty much the same, just tie in the ejector with 3mm elastic. Its easiest to push the elastic through the bottom of the body, then through the ejector, then tie your knots.
The author remixed this model.
Doubled up the silly pilot ejector then hollowed/added to the silly booster shell housing to accommodate the new ejector. Also lengthened and modified the original catch.