These are shot strings from my MRod 25, before and after being tuned.  The best performance came from my stock MRod with a Hammer Debounce Device.   All of the shot strings are from 3000 psi to 2000 psi, except the shot string "Paul's Tune with stock barrel and TT Reservoir Extension" which is from 3200 psi to 1875 psi.

Even with the added air capacity from the Talon Tunes Reservoir Extension, with Paul's "deep tune" and the LW barrel I purchased from him, I now get shorter shot strings with less power.

 

Below is a report on my tests with my stock MRod 25, with and without a Hammer Debounce Device.  This was done before Paul's tune.

 

REPORT ON EFFECT OF A HAMMER DEBOUNCE DEVICE
ON THE PERFORMANCE OF A BENJAMIN MARAUDER .25
by Frank S., Username: FS2020, Copyright ©  May 2012

On May 25, 2012, I added a Hammer Debounce Device (HDD) from AoA to my Marauder 25 caliber.  I measured the pellet velocity and pressure in the Marauder as a function of the number of shots, with and without the HDD.  I also recorded the sound report (both amplitude and frequency spectrum).  I used JSB Exact King 25.4 grain pellets for all tests.  Data was taken for a pressure range of 2900 to 1600 psig, with pressure measured on the Marauder gauge. 

Shots per Air Fill

The chart below shows the change in pressure as a function of the number of shots, with the initial pressure at 2900 and the final pressure at 1600 psig.  Results show that the HDD added eight additional shots over the abovementioned pressure range.  The trend in pressure reduction was also more linear with the HDD.

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Trend in Pellet Velocity

The chart below shows the profile of pellet velocity as a function of the number of shots, with and without the HDD. 

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The HDD produced a smoother velocity profile (i.e., less variance in velocity from shot-to-shot).  Less shot-to-shot variance in velocity will produce a tighter POI grouping.   The smoother velocity profile produced a “sweet spot” of 11 shots from around 2500 to 2100 psi as shown below.  The standard deviation in velocity over this pressure range was only +/- 2.5 fps around the average velocity 850.8 fps.  At 100 yards, this standard deviation in velocity would cause a variance in the point-of-impart (POI) of only +/- 0.25” (assuming all other conditions are ideal).  Without the HDD, the standard deviation over the pressure range of 2500 to 2100 was +/- 12.5fps.  An even tighter sweet spot with the HDD was the six shots from 2550 to 2350 psi, over which the standard deviation in velocity was less than +/- 1 fps. 

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Muzzle Energy

The HDD delivered a 21% increase in total muzzle energy output over the pressure range of 2900 to 1600 psig.  The total muzzle energy was 1243 ft-lbf without the HDD and 1508 ft-lbf with the HDD.    The peak muzzle energy decreased slightly from 43.3 ft-lbf to 41.2 ft-lbf.

Sound “Report” Signal

The sound produced by the Maruader firing with and without the HDD was recorded on a laptop microphone at a sample rate of 44.1 kHz with 16 bit resolution of sound amplitude.  The sound signals with and without the HHD are shown below.  All sound recording settings were the same with and without the HDD, and the plotting scales are the same with and without the HDD. 

The FFT frequency plot just shows the strength/intensity of the sound at different frequencies. Think of a piano. The sound frequency of each key increases from the left to right. Keys to the left emit lower frequencies (more bass sounds). Keys to the right higher frequencies (more treble sounds). When many keys are played at the same time, many sounds at different frequencies are emitting at the same time.  An FFT frequency plot would show which keys are being played and how hard they're being played. Here's a Wiki link that might help: http://en.wikipedia.org/wiki/Audio_frequency

MRod25_sound_without_HDD.jpg

MRod25_sound_with_HDD.jpg

The total magnitude of the energy of the sound signal is reduced slightly with the HDD.  Shown below are Fast Fourier Transform (FFT) analyses of the sound report signals.  The FFT plots below show the magnitude of the sound signal at various frequencies in the audible range.

FFT_MRod25_sound_without_HDD.jpg

FFT_of_MRod25_sound_with_HDD.jpg

Most of the sound energy is three peaks around 1250 Hz, 5000 Hz, and 17000 Hz.  Most people can’t hear well in the 17000 Hz (especially if you’re older like me).  So most of the “noise” is in the 1250 Hz and 5000 Hz peaks.  Notice that with the HDD the peak at 1250 Hz disappears and the peak around 5000 Hz is significantly damped.  A hypothesis for the disappearance of the 1250 Hz peak is that this peak was caused by the hammer “bouncing.”  More research would be required to confirm this hypothesis.  In general, to my ears, the sound of the report was less shrill and less unpleasant with the HDD.  It sounded more like a “poof” than a “crack.”

SUMMARY

Addition of the $35 HDD from AoA cost $35 and took 15 minutes to install.  For a pressure range of 2900 too 1600 psig, the HDD produced the following improvements:

·        Increased the number of shots from 31 to 39 for a pressure fill of 2900 to 1600 psig.

·        Total muzzle energy delivered increased by 21% with the HDD.

·        The profile of velocity as a function of number of shots was much smoother with less variance in velocity from shot-to-shot with the HDD.  This resulted in tighter POI groupings.

·        A “sweet spot” was produced over the pressure range of 2500 to 2100.  The standard deviation of velocity was only +/- 2.5 fps about an average velocity of 850 fps over this pressure range.

·        An even better sweet spot was from 2550 to 2350 psi, over which the standard deviation in velocity was less than +/- 1 fps.

·        The sound report was reduced at all audible frequencies, resulting in a less shrill and unpleasant report.