Magic Box Springs
 

Anyone know what kind of FPS I would get with a Magic Box M120 spring in a KWA KR9 (309mm inner barrel)?

Thanks

Well M120 usually means 120m/s or about 400fps.

depends on gun setup and spring manufacturer though... unless someone has first hand experience with the specific brand. Spring ratings are can only be somewhat reliable and relatable within the same brand, if you go x vs y brands, it could be different. I've seen one brand of m120s do 400 fps, I've seen some do 430, and that will also change with barrel length, bore and cylinder volume. If you have an extremely heavy piston or light weight piston assembly, that can also alter fps numbers a bit.

stock vfc springs in m4s which are m100s will get 400 fps when you put a 6.03 bore barrel on them.

With a shorter barrel and assuming it's 6.05 you're probably going to be around 370-380 at a guess.

By far the worst brand of cheap parts you can get.

I had random FPS from M110 and M120s in the SAME gun with them.

Avoid at all cost.

Yes, so that's why I said *about* 400FPS. Even the same spring can be significantly different in a different gun.