Google who?-300ft on 1 joule?-that would be something! As a matter of interest who did the other 'study'(Illustrations) you refer to? And at what fps/bb weight -I'm only wondering because at no point in the illustrations is the bb trajectory straight(even on exiting the barrell)
The first one was just to show how a ball bearing travels down a barrel.
While the other was showing how it bounces (And how the increments increase).
And search "LRB airsoft barrel"
And I was wrong, you can supposedly get 300ft with a gun shooting 350fps/.2g
However there are some hop-up units you can make that give the 300ft with a fairly straight trajectory.
E.G. the R-hop or the G-hop. In the summer, I'll be making a G-hop or two and might have a go with an R-hop in another gun (Maybe my sniper rifle)
Here is a G-hop - around 280ft shots on .79 of a joule (Makes the hassle of an LRB pointless and this is more accurate)
Or you can a buy ready-made R-hops online, they won't be as good as the G-hops you can make (My opinion).
Or for G36's (Won't work for any of my other guns for some reason) you can simply shave off the nub on conventional rubbers. and it'll add a little more range due to more uniform spread, flat hops are best though.
I am amazed at how un-informed we are in comparison to our American counter-parts. I wish we had easier access to compressed air up here, then I'd make a 50rps Polarstar engine powered BB gun which can be bumped to 500 fps when playing in England.
The only problem with all of this is that the shots will land like a butterfly, you most definitely won't feel them.
To OP, I would recommend Ultimate barrels but I wouldn't Guarder