Tuning First time trying tune my Dreamline .25...got questions

[Hummer57]

After watching a few YouTube videos I decided to try and tune my Dreamline for JSB 33.9 pellets. It was shooting the 25 Here. Pretty well, 1” at 50 yrds.. Chrono was around 870 for those. So I increased my regulator to 135/140 bar and started adjusting the HST. Screwed it all the way in and the lever wouldn’t cock. So I backed it out 3 turns and it cocked. Chrono was 830ish. Started increasing one turn at a time, after two turns it wouldn’t cock(lock). Backed it out all the way , 440 FPS. Went in two turns at a time until I got to 800 FPS. Two more turns and I was all the way in and was at 740 FPS. Started turning out two turns, now it won’t lock up. So I started over, 4 turns out in the 780 range. Finally got it to 860 FPS consistently.If I go more FPS drops. I did this numerous times and occasionally the bolt wouldn’t lock and I had to go through the process again. I can’t get my FPS over 866. What am I doing wrong???

 

[Glem.Chally]

You dont need that much spring, its hitting the valve so fast and hard its snapping shut again fast leading to lower power. Less is more to an extent with spring vs a moderate reg pressure. 870 with those pellets is almost 60fpe, you might be expecting too much speed from those pellets assuming your gun is stock.

If you want more power raise the reg a bit and stay a turn or two from max hammer spring. You don't really ever need to use that much preload (to the point it won't cock) its overly hard on things for no reason.

 

[Hummer57]

Ok, thanks. It is stock, no mods. Of note, it started out a tuned .22 from Spaw. I bought it used and the the owner put a .25 barrel on it. I’ll leave it where it is. I’ll shoot it today if it gets warm enough here and see how it groups. Do you think it’s worth buying one of those hst lock washer the guy was selling on hi video? Relatively inexpensive and the screw is very easy to turn. Thanks again!

 

[Glem.Chally]

Ok, thanks. It is stock, no mods. Of note, it started out a tuned .22 from Spaw. I bought it used and the the owner put a .25 barrel on it. I’ll leave it where it is. I’ll shoot it today if it gets warm enough here and see how it groups. Do you think it’s worth buying one of those hst lock washer the guy was selling on hi video? Relatively inexpensive and the screw is very easy to turn. Thanks again!

For the price of them I grabbed one also, might as well.

 

[Clifton]

I'm surprised you got 870 fps with 34G, 57 fpe on a stock gun. I had to add plenum and port the transfer port and could only get 59 fpe. The plenum add 15 fps by itself with the 34 g jsb's.

 

[Hummer57]

 866 was my max but could get 860 consistently. The 34 JSB had about a 3” drop from 30 yrds to 50 yrds. I went back to 25 gr JSB it’s shoot 1” groups at 50 yrds. How difficult is it to add a plenum?

 

[caesar]

It takes 5-10 minutes to add the plenum. Very easy. Airgundepot has a video on it for tube and bottle variant. 860 with 34gr is better than I was doing with a stock configured gun too. That’s more than the specification says the gun is capable of.  nice power! You *should* be able to get 34gr Heavies accurate at around 830-850fps. They seem to like slightly lower speeds than 25.4 Kings. 

 

[Clifton]

The 34 JSB had about a 3” drop from 30 yrds to 50 yrds.



That shouldn't be. Take a read of the first and try the second calculator. 

https://www.airgunnation.com/topic/what-distance-to-zero-in-scope/

http://www.airguns.net/trajectory.php