Mines just a 300mm GBB/VSR CJ barrel I had spare when I tried it in my Striker AS01
I think Tokyo Marui cut their stock barrels differently. So after market buckings dont work with their stock barrels. I tried to put a TNT bucking on a stock TM HK45 barrel and wouldnt fit at all.
This is most likely due to a stock barrel, being designed to with with a bucking with a standard contact patch, not one like Maple leaf, or TNT.