I recently got a KA (WA system) M4 GBBR. It was simple enough to swap out the high power valve blocker for the included low power valve blocker using the included instructions. Problem is I'm not sure if it's enough. It might still be shooting over 400 fps with a .2g BB. I have a plan for a DIY mod, but if there are tried and true methods for further reducing power I'd like to hear them.
I don't have a chronograph, but I'm planning on using my computer to conduct a sound test. I'll fire at a hard surface fixed a known distance away from my replica, record audio of my gun firing, and look at the waveform to find the time difference between firing and ricochet. I'll use the time and distance to calculate the average velocity. Then I'll move the target closer and calculate the new average. After a few data points have been collected at different distances I should be able to find the limit of the velocity as the distance approaches zero. That should approximate the muzzle velocity.
If I estimate it to shoot over 400 fps with a .2, I'll try modding my high-power valve blocker to look like my low-power valve blocker but slightly more-so. I don't want to modify my low-power valve blocker since it at least gets me close to a safe velocity and I don't want to risk damaging it.
So to those knowledgable about gas guns: does this seem like a good idea? Horrible idea? Is there a better method out there? Any feedback would be appreciated.