Magazine FPS issues

[Memphishills]

I am having a weird problem.

Worked on my amoeba last night to fix some compression issues. Upon testing the gun with a PMAG, I was getting the ~360 fps I was expecting. When I put in one of my Lancer Tactical Socom L5 mags I dropped down to ~275 fps. Thinking this was weird, I tried some CYMA mags and it went back up to the ~360, went back to the Lancer Tactical - ~275.

Now I have 10 of these mags at home (L5), and I tested each one, and they all drop the fps by ~70-100 fps.

I have also tested PMAGS, CYMA, Generic high caps, and a Lancer Tactical Troy mag (which is nearly identical in design to the L5) and all of those mags hold at the appropriate ~360 fps.

I used the same brand BBs for testing, all mags were tested from the same bag of BBs and my L5 mags have never been oiled, and are not dirty.

So I'm pretty stumped.

It's probably also important to note that the L5's feed fine, and fired every round without issue. No misfeeds, no double feeds, shot clean through the mag.

Any suggestions?

[ThunderCactus]

We have the same issue happen on PTWs, the springs aren't strong enough to feed or the followers are jamming up the mags.
Could be a tolerance issue too, but most likely the springs are too weak.

[RainyEyes]

Gonna take a shot in the dark here and ask that you turn the hop-up off completely (disengagd). Then try again.

The bb's might be pressing up against the hop-up too much causing it to lose fps. If there is a magazine spring tension difference between the two brands, then it might be the case that one is feeding bb's too hard into the hop-up.

This was the case for my aeg with a low-fps set up where my m90 spring shot 180 fps when the hop-up was engaged too much. Shoots 270~ with it off...