The average velocity of a stock HL gun is 80fps. I do not drill holes in the barrels, that is a myth that plays out when you measure velocities. I'm using Systema and Mad Bull airsoft barrels cut down to size, 207mm for the correct length for a Pershing and 234mm for the Tiger. Haven't figured the Panther or M41 out yet.

VS and Marui units use a breach with an actual hop up feature in them. This imparts the spin on the round when it leaves barrel and causes the upward trajectory. Using the .20g bbs makes for flatter trajectories and sacrifices velocity. Ohh, A stock VS A6 airsoft unit averages about 135fps. So does a Heng Long unit with a Systems 6.04mm barrel!

As for springs, I bought some from my local hardware store and ordered 8 from Century Spring Company. My goal with the parts is to arrive at my goal with parts that everyone can obtain so they may replicate the same performance, even years later. Right now I can consistantly break a paintball against a hard verticle surface from 13 feet. I want 15! Because of their smaller diameter the paintballs velocity averages 150fps during testing with the Systema 6.04mm barrels.

Other things to test out is the return spring on the outside, the diameter of the nozzle, use of spacer and or guide rods and lubrication. Tests with more powerful motors haven't contributed to a performance gain.

Anyone got a lathe? The weak link in these things is the breach, I'm constantly breaking them, in the stock airsoft units! Would be great if someone could turn them out in aluminum or a more durable plastic/polymer.