FX Impact M4 tuning advice!

[Benji1989]

Hi everyone. I'm a long term lurker but don't post very often. I have an impact M4 and was wondering what the optimum length of the C1 from the block is? It's a 700mm sniper in .22. I have a slug power kit to fit but won't be using the tungsten hammer or soft return spring if I can get 34gr slugs up to 1000fps and then lower for accuracy without too high of a reg pressure.
Also wondering if anyone can explain what the realistic differences are between the two hammers in the picture. They weigh a similar amount but the black delron part(C3?) is quite a bit longer on one of them than the other. Has anyone got any info?
Thanks in advance!

 

[Vetmx]

First, did you measure your C1 before you removed it? That’s where I set all my guns back to when I reassemble them. They all are a little different from gun to gun. The main thing about that measurement concerns getting back close to previously recorded tunes in your notes. If your gun was 6mm when you took it apart and you reassemble it at 7mm, your VLA setting will be different this time. Not the end of the world as long as you don’t venture too far beyond the general setting zone of the C1.

Second concerning your hammers, don’t worry about it. The delrin is there so you’re not metal on metal hitting the C1. I have three extra hammers in with my stuff and the Delrin is different on all three.

 

[rickschowengerdt]

I just went through the same thing. Resetting the C1. I called UA and ask the technician what the distance should be. And the reply was for optimum distance should be between 5.8 and 6.2 mm with the valverod seated all the way back into the valve body., if you can get there. I hope this helps.