Thanks for this great mod! I am just wondering, why not wrap the two holes on the barrel with tape then just cut away the tip, wouldn't this give you a longer barrel to fit the dart in? By the way, I saw it at target in Canada for just $8.99! (But I haven't pick one up yet...)
I did mod my pyragon, but the arm broke wasn't because the bumper. It just lost a little plastic on top, so the arm is still long enough to load the gun, but can't fire disks out. If proton's arm isn't as long as pyragon, it couldn't work at all (even they have similar mechanism)