FX FX IMPACT M4 - Hammer Upgrade

[Irish shooter]

I am currently tuning my M4 Impact to shoot 37gr Zans. I recently upgraded my hammer to the Huma Air 8.5-gram hammer and changed the pellet probe and hammer spring.

In the first instance, I achieved great results with slugs going 935- 955fps with my reg set between 120-125. Then I realized I forgot to change the valve spring upgrade and the rubber ball. When I added these, the speed dropped drastically to 830 even with my reg pressure up at 145.

I changed back to the original stock valve spring, and it's back up at 935 with reg pressure 120. which I'm happy with.

I don't understand how the lighter spring upgrade and the rubber ball cause such a drop in speed.

Do I need the rubber with the valve spring with an 8.5-gram human air hammer?

 

[Hobbyman2007]

The valve was bouncing off the stop. I think you have too much valve dwell and are wasting air. I’d bump up my regulator pressure to 150 and try it again. The shot cycle should sound like a snap not a swoosh. This is just my opinion though and could be totally off.

 

[Irish shooter]

The valve was bouncing off the stop. I think you have too much valve dwell and are wasting air. I’d bump up my regulator pressure to 150 and try it again. The shot cycle should sound like a snap not a swoosh. This is just my opinion though and could be totally off.

if I turn up my reg to 150, would I not be using more air than my reg at 125??

On another note perhaps don't need the rubber ball. I have just read on the Huma Air website the below on the valve spring. Looks like I don't need the rubber ball.

"When using this valve return spring in the M3 or an impact where the 720 plenum kit is fitted, the rubber ball should not be used. The new valve adjuster already has a rubber buffer installed, and adding this ball will result in a reduced stroke and loss in power."

 

[airman_o]

@IrishCracker I just did exactly the same, tuning for 33 grain slugs (in .22). At first I changed hammer, hammer spring and valve return spring. But in this setting I was overpowering the valve. After that I kept the 8,5gram hammer with the original hammer spring, and the original valve return spring. This works great.
Also, als you just indicated: I would do without the rubber ball.

Can you still reduce power with the macro/micro wheel with the stronger hammer spring? I would not, hence the change.
In the current settings (130 bar) I can reach 980 fps maxed out, which I reduce to 960 fps with lower tension on the hammer spring. Seems to shoot like a laser with very low ES.

 

[greenbeans]

I am currently tuning my M4 Impact to shoot 37gr Zans. I recently upgraded my hammer to the Huma Air 8.5-gram hammer and changed the pellet probe and hammer spring.

In the first instance, I achieved great results with slugs going 935- 955fps with my reg set between 120-125. Then I realized I forgot to change the valve spring upgrade and the rubber ball. When I added these, the speed dropped drastically to 830 even with my reg pressure up at 145.

I changed back to the original stock valve spring, and it's back up at 935 with reg pressure 120. which I'm happy with.

I don't understand how the lighter spring upgrade and the rubber ball cause such a drop in speed.

Do I need the rubber with the valve spring with an 8.5-gram human air hammer?

Leave the rubber ball out. M4 has it built in into the adjuster.

 

[Hobbyman2007]

Higher regulator pressure do not always make for higher air usage. For the most part it’s actually less. If you tune your rifle with the hammer maxing out the valve like you had , the valve is open longer than necessary. With a higher regulator pressure , you can have a higher shot count as the valve does not need to be opened as long to make the same power. It’s a balancing act.

 

[UDABEGGER]

Why different hammer weights . I go on the idea of increased reg pressure will at some point need a heaver hammer to get added power from reg increase . What am I missing in my thinking ?