Ok here goes I will try to simplify my theory down a bit so everyone can understand: basicly energy cannot be created or destroyed, it can only be converted, eg kinetic into heat, chemical into kinetic ect. Knex guns are no exception, the enery has to come from somewhere, in most guns this takes the form of pulling back a pin or rubberbands to create potential energy, this is released when the trigger is pulled, this potential energy is converted into kinetc energy and this is how the bullet is fired. A semi automatic gun is required to fire every time the trigger is pulled, but the energy still has to come from somewhere. RBG's take this into account as each band is pulled back and has potential energy stored, however many knexer's opinions differ on whether this is truly semi automatic, many calling this type of gun a psuedo semi auto. Other guns use the energy imparted on pulling the trigger to create the potential energy to power the bullet, this is considered to be a true semi auto, however the main drawback of this system is that the amount of energy that can be transfered from the trigger to the bullet is very limited, therefore this type of mechinism has limited power. So if the problem is energy how do we solve this? one possible answer is to have an extra source of energy, such as a motor or a winding system that puts extra energy back into the system, however this approach will not give you a "true" semi auto as you will have to have an external source of energy, that and the fact that knex motors do not have the power and torque needed for this system. So what's your opinion, do you have anything to add?