How does a NERF DOUBLESTRIKE work?

I am filming this because Covid-19 won't let me leave the house...So what else to do but take apart a nerf gun.

[lisianepiazza]

Do You have a idea on how can we mod this gun to shot gel balls and with hight capacity, which means whe goin need a way to the piston cylinder to move a little to backwards to alow balls to enter the barrel and then foward again to seal ?
If the cylinder movent cant happen then how about instaling a shot tube at the piston like the daisy red rider ?