it would take almost a entire new gun thing to render a airsoft gun into a working model that would fire live ammo.
With respect to an AEG, you are correct. But with a GBB rifle, at face value you are not.
I did see this on the retailer-in-question's website, I found this new release by them:
Now we at Airsoft Outlet Northwest, being the rational individuals we are, went out and had a gunsmith check the true compatibility of these replicas and found the following information:
* The WE TTI M4's lack any sort of functional gas tube which is integral to an AR15's operation
* The upper receiver of an AR15 fits onto the lower of the WE TTI M4
* The stock trigger pack in the WE TTI cannot strike the firing pin of a AR15 bolt
* The body of the WE TTI lower is several mils thinner than an AR15 lower, and shims would be needed for any AR trigger pack to work
* The trigger pack of an AR15 appears to be able to fit onto the lower receiver of a WE TTI M4, one of the AR15 trigger pack retaining pins is impossible to insert without major modification, and the hammer isn't operable with the WE TTI lower.
So essentially these Airsoft replicas cannot even operate an AR15 trigger pack without heavy modification with a precise tooling system operated by someone who knows the specific measurements to drill and tap the WE TTI lower receiver.
To me this doesn't sound like it's feasible within "a short period of time".
So apparently it is not as easy as it appears at face value to convert a GBB M4 lower to function a real steal M4 upper