FX Impact M3 Compact with Heavy Valve Return Spring?

[Squirrelmageddon]

My Compact .22 came with the heavy valve spring. It's 1mm OD wire and the standard spring is .75mm OD. Can any other Compact owners chime in on what spring came in their Compact? I don't know why the Compact came with the heavy spring labeled (harder spring on .22 sniper). I'm thinking it was a fluke.

 

[Vetmx]

It would make sense because of the barrel length and FX anticipating what Americans are going to try to do with the gun. I have a 600 and two 500mm Impacts but never compared the valve springs. I’m a firm believer in using what FX puts in my gun when it comes to the valve spring and weight of the hammer. But I do see your concern. You’ll know when you start tuning it.

 

[Squirrelmageddon]

FX support confirmed that the compact is supposed to be using the softer #1301 spring. No wonder my tunes are way off stock settings.

 

[carlos_hathcock]

It would make sense because of the barrel length and FX anticipating what Americans are going to try to do with the gun. I have a 600 and two 500mm Impacts but never compared the valve springs. I’m a firm believer in using what FX puts in my gun when it comes to the valve spring and weight of the hammer. But I do see your concern. You’ll know when you start tuning it.

So I have a buddy who is knowledgeable with Impacts helping figure some things out and he felt my stock (harder) valve spring was too strong and limiting my valve's adjustability. Today we tried the softer spring and it gained about 35 FPS even though the adjuster had been out to 5 1/2! It doesn't make sense to me that a 700mm would want a harder spring, which I believe would give shorter valve dwell, and a shorter barrel would want a softer spring. Couldn't a longer runway make use of greater dwell? What am I missing? Some balance or harmonic consideration? It still shot well at 100 yards.
Anyway, I've got some more fiddling to do but it seems the rifle can make more velocity now with less effort simply by removing the bottle and shroud, unscrewing the valve adjuster, and swapping the spring. My buddy seems to think FX sells the rifle with an 18 grain pellet in mind while I'm shooting 25+ grain slugs.

 

[Vetmx]

Gaining 35fps is easy if you don’t mind wasting air. That includes all guns. I could take apart a Chinese budget rifle, put a weaker valve return spring in it and pick up velocity. I’ve never had a 700mm barrel. But if I did and noticed my velocity kept increasing as I backed the knob out past the last line, then I would switch to a lighter spring. I can only speak on behalf of what comes in the 500 and 600mm M3’s. The spring is fine. And I have used a 600mm at times on the one gun that was purchased as a 500mm. A 700mm with certain reg settings and projectile weights could be a whole different animal and benefit from a lighter spring. You’ll know if you went too light when you take a look at your rubber balls inside the valve knob. If they are smashed, that’s not good because that means you’re relying on them. You’re blowing right through the spring rate like it’s not even there.