New hammer spring in crown mk2

[Gambler]

In my attempt to try and get decent fps out of my crown mk2 i have bought a stiffer spring from huma air.
Out of the box i cant get the crown to shoot more than 890 with 13.4gr at 140bar and max internal HS adjuster.
Someone told me that I May have a weak spring so I bought one from huma.
I have also drilled a bigger TP in my barrel from 3.5mm to 5mm and that didnt do anything to my fps.
But now I see that the air go into a hole in my pellet probe and out and that has to be the restriction that holds everything i do back, so Will this new spring actualy help me in this matter or is a slug/pin probe a better upgrade?
It dosent help with bigger hole in my TP when the hole in the probe is much smaller?

 

[madeintheuk]

You should get more speed than that. I found issues with my speed in my brand new mk2, and found out the spring had broken. Put a new one in, and I can get 25.39 22cal jsb to 930 in a 380mm barrel with reg at 145. I think that’s plenty for stock spring.

That heavier spring will give you some tougher cocking too. I would have got the heavy hammer kit huma Carries if you really want to test. It allows you to use different weight hammers without needing a heavy spring.

 

[gfmiller58]

I ran into an issue with my Crown, you may want to check. The front adjuster wheel restricts the airflow. Mine had worked loose and while showing max power was actually restricting the air, reducing power. Good luck.

 

[DNF]

Something else is going on, you should be damn near supersonic with 14gr @ 140 reg and max HS.

 

[Raider03]

Hi, what caliber is the crown?

 

[Gambler]

Ohh, .177. But as I can see, there is no point in having 5mm tp hole when the hole in pellet probe is 3mm?

 

[DanT55]

I would try turning your reg down to 110 or so and work up. You may need more hammer weight as well at 140 which seem way high for .177.

 

[Gambler]

So I should get 900+ fps at 110bar ?

 

[Raider03]

I had my MKI crown setup with a 500mm 177 barrel. I was able to get 960fps with 13.43 JBS Monsters.
The reg was set to 130bar.
With the hammer wheel at MAX and the hammer cock, the distances from the end of channel the fine hammer adjuster rides in to the hammer adjuster was 18.76mm.
I did install a Huma dual transfer port on the barrel.
I will post a photo to better explain that distances measure...

 

[Raider03]

From my notes ( not saying this the best tune, but your MKII with a larger plenum should be able to easily reach this velocity )

 

[madeintheuk]

So if your hammer spring is ok. Try tuning like this;

Lower reg as said to about 110b
Max out hammer spring preload with both wheel and Allen key.
Put in chrono, and slowly raise reg pressure till it plateaues in speed. This is the max your rifle will get in its current config. Then, dial the hammer down till you get your desired speed. This will make for a super efficient tune at the speed you want, but more importantly, you’ll figure out if your gun is capable of that speed. Remember, at 145b, that hammer has to hit the valve much harder to get it to open. If the hammer isn’t heavy enough for that pressure, your speed will decrease bc you’re over the plateau (knee).

Try this and get back to us with your results. Good luck.

 

[Gambler]

Ill try those numbers tomorrow and report back

But I have bad feelings on my madbull chrono also, like last time i used it i shot 870-890 with 13.4gr but I had one as high as 980 and one down in 550 range, but they still hit same spot on my 50m target.

 

[madeintheuk]

Sounds like a chrony issue for sure. That’s a huge speed spread not to lose even a little poi.

 

[18.13]

Sounds like reg is way too high, I have my .25 at 115b

 

[Gambler]

So if your hammer spring is ok. Try tuning like this;

Lower reg as said to about 110b
Max out hammer spring preload with both wheel and Allen key.
Put in chrono, and slowly raise reg pressure till it plateaues in speed. This is the max your rifle will get in its current config. Then, dial the hammer down till you get your desired speed. This will make for a super efficient tune at the speed you want, but more importantly, you’ll figure out if your gun is capable of that speed. Remember, at 145b, that hammer has to hit the valve much harder to get it to open. If the hammer isn’t heavy enough for that pressure, your speed will decrease bc you’re over the plateau (knee).

Try this and get back to us with your results. Good luck.

I have tried this now and I caps out at 135-140bar at 880-890fps with 13.4gr if I go 145, 150 the fps drops again

 

[madeintheuk]

I have tried this now and I caps out at 135-140bar at 880-890fps with 13.4gr if I go 145, 150 the fps drops again

So did you remove your hammer spring and check for damage? That would be my next step.

That little break was all it took. Put the new spring in and I was off to the races.

 

[Gambler]

I have not taken it out for a look, ill try tomorrow

 

[Gambler]

The spring looks ok so I dont know.
I get 830fps with 110bar and 890 with 140bar, same hammer settings. On 140bar i get around same fps from 11-23 on my hammer wheel tho.

 

[madeintheuk]

That’s usually too much hammer if the speed stays the same. Try going up to 150. That’s about max on the crown reg. See what the speed does. Also, make sure your transfer port in on its highest setting, and your barrel is properly seated.

 

[Gambler]

If I go 150 (i have tried 160 too) the fps drops to 650-700