[1tonne]

You said you have issues with double feeding. This is an easy fix. Get a new spring for the black part in the hopup that moved up and down and allows bb's through. If the spring is getting weak then it tends to let 2 bb's though. This is common when using a Deep Fire 55 round mag. (You can use a spare spring from a selector switch/cut off leaver from an AEG if you have one spare)
When a mag gets old the springs inside them tend to weaken and this can be a common cause of miss-feeding (not feeding). Pull the mag apart and stretch the spring. (They can be difficult to put back together so don't stretch it too much). Also clean the inside of the mag with a bit of silicone spray and then wipe it all off again. Mag can get residue in them that can makes the bb's get stuck. It's a similar residue like what you get in your inner barrel.
If these tips don't work then it is not the mags. It is an issue with the gun.

 

[1tonne]

Yip. The TM mag and the JG mags are the best. I prefer the TM mags as the spring is a little longer and so it keeps it's strength for longer. But I use both JG and TM.

 

[1tonne]

I actually read the opposite. Apparently the 55 round ones have a spring that is too strong and causes double feeding and jams. I guess it overpowers the small spring behind the double feed preventer in the hop up. That's exactly why I don't like this system. It's an unreliable balance of springs, while the L96 can't feed another bb without a deliberate bolt cycle.

The extra strong spring in the Deep Fire mag can overload the little spring in the hopup especially if the hopup spring is not new. So you could say that it is partly because of the mag and partly the hopup spring. If you use normal 30 round mags you will not have the issue. If you do it would be once in a very blue moon.
Most people would say the VSR hopup is a good hopup apart from the right hand curve.
But to be honest, I changed my hopup to an Action Army one and now I do not have feeding issues with the hopup. Only issues with the mag if the spring is old.