Tuning Diana Chaser .177 pistol, 150 shots

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nobody1

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Sep 4, 2021
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WA, United States
I like CO2 air guns as .177 pistols, lower powered and with lots of shots for target shooting.

I prefer CO2 pellet (as opposed to BB replicas) pistols, and my favorites are Diana Chaser and the Crosman 2240.
Diana Chaser is better all around than the 2240.

I have tuned a .177 Chaser pistol to shoot 150 shots on 1 CO2 cartridge.

With 7 grain pellets the first 90 shots were in the 340-360 FPS range, and shots 90 through 150 were in the 360 to 430 FPS range.
Yes, the velocity climbed up to about shot 135 and peaked at 425-430 FPS then went down and reached about 340 FPS at shot 150.
The temperature was in the 60-70 range.

I have almost got bored shooting all those shots in one session but wanted to count the number of useable shots.

To tune it that way I used a shorter and stiffer hammer spring, so short that it rattles in the air gun.
 
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I have replaced the spring last year.
I do not remember the dimensions.

The main thing is to have a ticker wire than the original hammer spring.
If the original hammer spring has 0.8mm wire then try using 1mm wire.

Initially cut the new hammer spring (with a ticker wire) close to the original hammer spring.
Shoot a few shots and measure the velocity.
At first the velocity may be higher.
Keep cutting the hammer spring (less than 1 coil) and measure the velocity.

When you get to the velocity range you want then stop cutting.
 
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Hold_Over said:
Are the mechanics of the chaser similar to or the same as the airbug?
Click to expand...
The mechanics are the same, possible exception would be the triggers in the latest Chasers. Formerly the Chaser and Airbug shared the same Diana DIT trigger, but the lastest Chasers seem to have a similar, but slightly different trigger as they have eliminated the adjustment screw in the trigger bow of the Chaser. The Airbugs still use the DIT (that would be AKA the "Diana Improved Trigger"). Though the DIT is easier to adjust, both triggers can be tuned for a very crisp/light pull.
 
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nobody1 said:
I measured the hammer spring I have.
These are the dimensions:
-wire 1.2 mm
-outer diameter 10 mm
-length around 54-55 mm

This spring was cut from a longer spring until I got the shot count I wanted.
Click to expand...
Hello @nobody1

Thanks for sharing this info. Can you give me the number of coils remaining in the 55mm length? By any chance do you know the material, ( stainless, piano wire, hard drawn ? ) , that would really help.

Thanks again,
ThomasT
 
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