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rsterne · Moderator

I spent some time the past couple of days seeing if I could record the signature of the muzzle blast and see if I could find evidence of hammer bounce.... I tried a series of shots with my 2560 HPA, and here are the results.... The time period shown is 0.1 sec (100 mS)....

I recorded the shot using a cheap microphone and an audio editing program called Audacity, and the result was a confusing mass of sound traces.... I tried various filters, and discovered that by using a low pass filter set at 89 Hz (a default) I got the above traces.... The resonant frequency is, in theory, about 33 Hz. for the hammer in my gun, so the filter was set high enough to capture that but eliminate all the "noise" of the blast.... Again, in theory, the 1/2 period that the hammer spends clear of the valve stem (based on it's weight and the spring rate) is theoretically about 15 mS (or less because of slight preload).... I did a recording of the hammer only (no air pressure) and the period was about 19 mS.... With air in the valve it should be shorter....

I can tell you that when fired, this gun sounds like the hammer is bouncing below 1000 psi, no question.... It MAY be bouncing at 1200 psi, judging by the sound, but it was hard to tell.... Above that, I can't hear any bounce.... I have no idea if the above traces can be considered reliable or not, although I did two of each and they were pretty consistent.... but it sure looks to me like there is hammer bounce occurring at the lower two pressures, not at the higher two pressures, and a transition is occuring at 1400 psi.... Incidently, the way the hammer preload is currently adjusted, the velocity peaks at between 1500-1600 psi at just over 950 fps....

This data is wide open to interpretation.... and I'm just offering my opinion of what I see in the traces....

Bob

Slavia · Moderator

I would agree with your interpretation. It definitely looks like those big spikes are being extinguished before 1400 PSI.

I have used the same setup with springers. I usually look at the overall shape of the sound envelope, which is in a way a mental low-pass filter. Thanks for the tip about letting the software do the work.

For those of you that might wish to try this, all you need is a $5.00 microphone plugged into the computer. The Audacity software is a free download - just Google "audacity" and you"ll find a zillion download sites.

radar · Silver Status Member

I hope you don't mind, Bob; I took the liberty of copying and reposting this image just so I could squish it down. I can see the patterns better, that's all.
There is two definite bounces there followed by two minor, that almost turn into one major pulse, then completely to one major pulse...

rsterne · Moderator

I would agree, the hammer bounce is pretty noticable in the first two, disappearing at 1400 psi, and gone by 1600 psi....

Bob