THese things are great.
So far, MadBull is the only off-the-shelf manufacturer I've seen selling a reasonably priced PSG1-length tightbore that isn't so tight that it lams up on 5.95mm pellets when it gets cold outside.
I'm looking at you, EDGI.
The barrel is lightweight due to its construction, and with the addition of a bore-up cylinder and used in conjunction with a proper hopup, will turn just about any standard-gearbox gun into a pretty hellacious DMR or countersniper weapon.
I currently have one of these in my King Arms L1A1-SLR shooting about 360FPS on .20s. I regularly load G&G .28's because of their precision and extra mass, and can group less than 15" at two hundred feet.
HIGHLY recommend MadBull's barrel series to anyone looking for a core upgrade.
Good material (7074 alloy aircraft aluminum)
Easy drop-in installation, as expected
It won't get the newspaper in the morning.
Madbull doesn't make a 618mm core for my RPK or a 116mm core for my Vz. 61.