[ThunderCactus]

So a regular problem occurred to me with my vector; I'd fill the 49rnd mag with propane and it would only get 20 rounds out before getting empty.
Okay well no big deal, I'm no GBB expert but I'm fluent with all things mechanical so no problem.

Just so happens I have a PAIR of vectors (one HK with cqb valve, one US all stock), so first thing I did was rule out the gun.
Same results on both guns. Chances of the exact same failure on both guns at the same time, slim but possible.
Take both air nozzles apart and find nothing amiss.

Try another mag, and it works perfectly. fired 60+ shots on both guns.
Okay perfect, I've got one good mag and one bad mag, perfect for testing!
swapped valves, air nozzle seals, feed lips, same effect. Inner brass fill tubes are the same length as well.
Real head scratcher at this point.....
Two of the exact same mags, interchange the components and for some reason it doesn't work the same....

Only thing I hadn't swapped out was the fill valves.
Well, only one thing to do! Swap out fill valves and sure enough, that's the damn issue.

Now, how can a fill valve be a problem? Really wtf.
I don't see how it could be an issue since you're pouring propane liquid in, and the gas pressure is forcing the liquid down.
Maybe there's a swelled Oring or fouling slowing the flow of liquid propane, and the liquid is turning to vapor which prematurely pressurizes the mag? I don't actually know enough about pressurized gas physics to say for sure. All I know is I need a few new fill valves lol