[becklr1]

The regular 11mm spring you can get to that rate at the top end of the line. http://x-fire.org/etop/bolt_sp.html

Then there is the 13mm line as well. http://x-fire.org/etop/bolt_sp_thicker.html

I was able to record 450 with a VSR 250 and a .25 BB with a 550mm 6.01 barrel.

You can buy right from them as well using email.

Good luck!

 

[becklr1]

Check the links I posted it says which is 11 and 13.