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Analysis HDD improvements on a MRod 25

May 26 2012 at 8:39 PM
Frank  (Login FS2020)

I just installed a Hammer Debounce Device (HDD) on my MRod .25. I took velocity, pressure and acoustic data before and after installing the HDD. I got moderate increases in shot count per fill (8 additional shots). The most significant improvement was that the velocity profile was much smoother (less shot-to-shot variance in velocity). The HDD produced a sweet spot of 11 shots from 2500 to 2100 psi with a standard deviation in velocity of only +/- 2.5 fps. From 2500 to 2300 the standard deviation was less than +/- 1fps for six shots.
My engineering analysis of the HDD performance can be found at
I also present a spectral analysis of the improvement in report acoustics.
I'm an engineer but somewhat new to air guns. I'm just starting to learn how to tune the MRod 25. Any advice is appreciated.
Frank, username = FS2020
ps: Does anyone have the differential equations describing the gas expansion and pellet velocity from an air gun reservoir? I assume this problem can be approached by placing a control volume around the expanding air. I'm working on solving it now, but I'm sure someone has solved this and programmed the differential equations already. I'm an old timer and still program in Intel Fortran.

This message has been edited by FS2020 on May 29, 2012 3:45 PM

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