Madbull ultiamte hopup, double feeding issues
 

I have a madbull ultimate hopup, with a guarder clear rubber, and a Mad Bull 6.01mm Ultimate Tightbore Barrel. theres no fitting issues in the hopup itself. I used a water based lube to assemble it, and its all lined up properly. At first I thought the hop was set too low, but even at its max setting its double feeding.

Im also having troubles getting mags to sit properly.

I don't have the double feed issue, but my mags I have to give an extra shove to get them to seat and feed. Not to mention that since I installed it my FPS went up to 465fps with 0.20gr bb's.

Re: Madbull ultiamte hopup, double feeding issues
 

Use the supplied blue madbull rubber. I tried the clear and it will tear. It fits too loose over the mb tbb that it will move and eventually tear.

I tore up my blue rubber, had to replace it. The aluminum barrels arent the same as the teflon ones there slightly bigger, theres no movement in the rubber at all.

Madbull ultiamte hopup, double feeding issues
 

What I meant by the clear fits too loose is not only over the barrel but also inside the hopup. The lips of the rubber done sit flush. That's what tore on mine. The nozzel is actually what caused the tear.

If the mb blue rubber fits snug on your inner barrel then that would be for the better.