Tuning FX M4 .22/.35 BC Data & Starting Tune Settings

[OZFeral]

G'Day Everyone,

New to the forum and recently picked up an FX M4 800mm in both .22 and .35 calibers. I'm diving into the world of precision air gunning for hunting and want to get the most out of the rifle.

I'm currently in the process of gathering data to feed into my ballistic calculator (Alpex 4K) and would greatly appreciate any insights the community might have on the ballistic coefficients (BCs) for various grains of slugs and pellets commonly used in these calibers. I've already started checking manufacturer websites and some review sites, as I understand BC is specific to the projectile.

In addition to BC data, I'm also looking for general starting points for regulator and hammer spring tension for different projectile weights and types in both .22 and .35. I know these settings are highly individual to the rifle and the desired velocity, and a chronograph is essential for proper tuning. My plan is to start with conservative regulator pressures (around 120-140 BAR for pellets and potentially higher for slugs) and mid-range hammer spring settings, then carefully adjust while monitoring velocity to find the sweet spot for accuracy and consistency. I'm also mindful of balancing power with shot count.

Given the STX barrel system, I'm aware that different liners and projectiles might have unique optimal settings. Any experience or data you can share regarding specific slug/pellet combinations and their associated BCs, along with approximate starting regulator and hammer spring settings that have worked well for you on your FX M4 (.22 or .35), would be incredibly helpful in speeding up my initial tuning process and minimizing wasted ammo.

Slugs and Pellets Purchased:

Brand​	Type​	Caliber​	Type	Grain​	Batch​
JSB	Exact Hades	.35	Pellet	77.16
JSB	Exact	.35	Pellet	81.01
JSB	Exact Jumbo Heavy	.22	Pellet	18.13	84060024
JSB	Exact Jumbo RS	.22	Pellet	13.43
JSB	Hades	.22	Pellet	15.89
NSA	HPFB	.35	Slug	93
JSB	Knockout MK II	.22	Slug	25.39

Thanks in advance for any guidance you can offer! Looking forward to being an active member of the community.

OZFeral.

 

[6gun]

I need to preface with my gun is a 22 m3 700mm with a tungsten hammer. M3 to m4 won't have any significant bearing on what I write. You the barrel length might have you running a bit fast.

I was super cautious like you when I got it too but I can say fear not. If you do not exceed the max pressure in the manual you'll be safe, maybe not the power you want immediately but the gun won't be hurt. I'd start at 140 but your light pellets are probably not going to be useful

Projectile data - strelok has the best data set imho and you can still get the calculator from the Russian guys website. The app stores dropped his app for political reasons unfortunately. Hard Air magazine has some good listing's too.

22 tune. The hammer weight will dictate your performance envelope to a degree. I went down the increased spring rate route and it was too violent and inconsistent for me, so I went the heavy hammer route. Another user put it this way "the tungsten hammer doesn't really start to find it's groove till 150 bar" i was trying to stay lower for a shot count reason but it wasn't in harmony. I set the reg to 150 and I got the harmony and precision I wanted. That said, the combo at that pressure allows me 1 pellet and at least the 3 slugs I wanted to shoot.

Jsb monster redesign /heavy hades 25gr
Patriot javelin 23gr
NSA 31gr
Patriot javelin 34gr

What caliber did your gun come in from the factory? The 35 got a heavy hammer in the m3 era and the 22 came with a rather light one.

If you strive to tune the best you can it's going to be a bit of an adventure for you. I hope all this is of some use to you.

Just for fun.
700mm 22
150 bar
VA 4th line.
Micro 3.5
Power wheel-(1) jsb monster/23 javs
(8) 31 nsa
(9) 34 jav.
Everything is around 980fps except the 23 jav going a little over 1k. The trajectories are similar enough for the intended use of the projectile that it made me think the calculator was busted.

 

[markhooper]

I guess this probably doesn't belong, but I have heard about the bc calculator before being unavailable because of political reasons.. so is the attaman ap16 compact.. now if we could just get the moderators on the forum to remove the political reasons why we can or can not get a certain thing it would be awesome.. but again that's wishful thinking..

if any of you moderators read this you are doing a awesome job with this site..

I guess I'm just lamenting that we even have to be affected by political things even if we don't care to.
hope you all are doing great. have a great evening
Mark