All you guys that reload, check this for accuracy. I think it's pretty close to being right. Anyone that knows Marauders, have a look as well, it's my learning of the gun if you will!
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Tuning a Marauder, like reloading bulletsAs far as I know, there are three major elements to reloading for powder burners:
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Tuning a Marauder, like reloading bulletsAs far as I know, there are three major elements to reloading for powder burners:
- Bullet Weight = Mass
- Amount of powder = potential energy
- Speed that the powder burns = speed energy is released
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Tuning an airgun can be compared to reloading for powder burners like this- Bullet weight = Pellet weight. Heavier pellets using the same amount of energy (Powder) move slower. Lighter pellets, using the same energy (Powder)move faster.
- Amount of powder = Hammer adjustments = the amount of air (Powder) used for each shot. So, the Hammer Spring Preload and the Hammer Stroke adjustments are the equivalent of changing the amount of powder used for each shot.
- Powder burn rate = transfer port or Valve Metering Screw adjustment. Opening the port to allow faster air transfer from the air supply = faster burning powder and slowing the air transfer by closing the adjustment is the equivalent of using slower burning powder.
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Number of shots per fill are controlled by Hammer spring adjustments as the hammer spring adjustments determine how much air is used on each shot. Heavier hammer spring adjustments for more power uses air at a faster rate, and reduces the number of shots per fill. Lighter adjustments use less air and increase the number of shots per fill, but supply less energy per shot.
The velocity is controlled by the Valve Metering Screw. Closed means slower velocities while open means higher velocities
So, when tuning, decide what you want, higher velocities or higher shot count. By the way, my particular Marauder tops at about 35 shots per fill, no matter how it's adjusted. If you want max shot count, start at the Crosman recommended factory settings. In .22 it'll fire a 14.3 Premier Dome at around 830 fps. The chrony string I did shows 6 fps Standard Deviation, so it's an excellent setting to start with. The settings maximize shot count and are:
Caliber Hammer Tension Hammer Stroke Transfer Port
.177 1.5 5.5 2.125
.22 1.25 4 2.5
.25 5 4 4
In .22, the Crosman Premier Dome 14.3 flies at around 830 fps. The JSB Exact Heavy at 18.3 grain flies at around 750 fps. My goal is to get the JSB Heavy's to about 830 fps.I ran some initial tests where I adjusted the Hammer Tension, and upped the Valve Metering Screw to 4. This did achieve the 830 fps I was after, but at the cost of more air. Remember the .25 Marauder is rated at 16 shots per fill, and I wanted to have closer to 30, so back to the drawing board.
As a side note, I have used the Hammer Adjustments to get the JSB Heavy pellets to 830 FPS in the past, but only got 20 shots per fill, meaning I was wasting a lot of air. This whole experiment is to see if I could get the JSB Heavies to fly around 830 fps, and get more shots per fill.
So, using the reloaders comparison, my powder load per shell is the most economical I can use with the hammer tension and Preload set to factory Crosman specifications. The only thing left to play with is the burn rate or the Valve Metering Screw.
I set the Valve Metering Screw to 4, and the shot string of 30 averaged out at 842 fps, but with quite a variance is speeds. Standard Deviation was 21.83 with the high of 877 and the low of 801.
There could be other elements in play as well. The O-Rings could be a bit worn and such, so I'll look at replacing the o-rings and ensuring everhtying is properly lubed.Work will need to wait a while now, as my air tanks need to be re-certified. That'll take a couple weeks.
My next step may be a Huma Regulator. It's only $125 and should really even out the shot string and might give me a few extra shots per fill. It's all an experiment, so I'll keep you posted.