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PostPosted: Wed Apr 29, 2015 3:12 pm 
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Location: Burnstown, Ontario
So, I replaced the spring in my Crosman .22 Phantom, and it really packs a wallop compared to the old spring. Pointed pellets can go through 3/8" plywood and it's much louder. But I'm surprised it's only marginally above 500 FPS. I don't have a crony, but I recorded a wave file of it hitting a target 218 feet away. Subtracting 1,127 FPS for the speed of sound at 21C, it gets there in .392 seconds. I used a wave file editor to get that time measurement... I did the math twice. I'm only getting 556 FPS.

This sound right? The spring is supposedly the non-dumbed down version for this rifle. :?

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PostPosted: Wed Apr 29, 2015 3:17 pm 
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How far is your mic from the muzzle? How far from the target? Did you take that into account in your calcs?

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PostPosted: Wed Apr 29, 2015 3:24 pm 
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Does your Phantom have the bleed hole in the piston?....

Bob

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PostPosted: Wed Apr 29, 2015 3:57 pm 
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Also don't forget that the speed of sound is generally measured at sea level, so changes with altitude. And humidity affects it as well. Too many variables I would think for the Mic chronograph to really be accurate. I could be wrong but that's my opinion.


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PostPosted: Wed Apr 29, 2015 4:12 pm 
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Thanks everyone - here's some answers:

- The mic was about 4 feet from the muzzle... insignifiant really.
- I'm about 250' above sea level.
- Definitely no hole in the piston
- I'm 218 feet from the target

I was expecting almost 700fps because of this video: https://www.youtube.com/watch?v=wFCbU9QznJ0

Perhaps I am indeed getting that, but it could be the variables in my method are messing me up. I'll try and attach the wave file...

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PostPosted: Wed Apr 29, 2015 4:19 pm 
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It appears that you are measuring the time it takes for the pellet to get from the muzzle to target. The average velocity appears to be what you are calculating. The velocity at the muzzle will be higher, and the velocity at the point of impact will be slower (obviously). Your range you are using is approx 70 meters. I'm guessing that your initial velocity is in the area of 650-700 fps, maybe higher depending on the type of pellet you use. A real chronograph will give you a better idea of just how fast your new spring is. Just my .02.

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PostPosted: Wed Apr 29, 2015 4:25 pm 
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I haven't done any of the math, but have you taken into account the fact that the pellet slows down from the moment it leaves the barrel and that an average velocity is just that -- the average speed the pellet had from the time it left the muzzle to when it hits the target. If the average velocity is 556 fps, the muzzle velocity would be significantly higher.

Hawke Chairgun shows that a pointed Crosman 14.3 grain .22 pellet starting at 675s will take 0.369 seconds to travel 70 yards or 210 feet. At that distance, it will be going 483 fps.

This method of calculating pellet velocity is no substitute for results obtained using a chronograph.


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PostPosted: Wed Apr 29, 2015 4:27 pm 
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Have you tried chronoconnect?
And do you have the short or long piston? My phantom with a lube and tune and plugged hole was shooting 660 with 14.3gr pellets.

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PostPosted: Wed Apr 29, 2015 4:30 pm 
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Hominid wrote:
don't have a crony, but I recorded a wave file of it hitting a target 218 feet away. :?

that's way to far for a sound file, you don't need to be that far away....50ft will give you a much better result and a more
accurate sound file... :wink:

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PostPosted: Wed Apr 29, 2015 4:39 pm 
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DigitalFx33 wrote:
Have you tried chronoconnect?
And do you have the short or long piston? My phantom with a lube and tune and plugged hole was shooting 660 with 14.3gr pellets.


Don't know what chronoconnect is... I'll google it. And neither do I know what length of piston I have, but there was no hole to plug...

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PostPosted: Wed Apr 29, 2015 4:41 pm 
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Penage Guy wrote:
I haven't done any of the math, but have you taken into account the fact that the pellet slows down from the moment it leaves the barrel and that an average velocity is just that -- the average speed the pellet had from the time it left the muzzle to when it hits the target. If the average velocity is 556 fps, the muzzle velocity would be significantly higher.

Hawke Chairgun shows that a pointed Crosman 14.3 grain .22 pellet starting at 675s will take 0.369 seconds to travel 70 yards or 210 feet. At that distance, it will be going 483 fps.

This method of calculating pellet velocity is no substitute for results obtained using a chronograph.


This interestingly sounds close to what I'm getting, and I am using a pointed pellet.

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PostPosted: Wed Apr 29, 2015 4:46 pm 
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Probably a really obvious and stupid question, but... have you remembered to account for the fact that if the mic is at the muzzle location and you're recording the sound of the impact and measuring the difference between them... that the sound actually takes just as long to get back to the mic as it takes to get from the muzzle to the target? Not at all sure of the math needed to factor that in along with decreasing velocity of the pellet and other variables, but if you're taking the total duration of the sound as being the time it took for the pellet to get to the target then you're off by a LARGE factor. At a very rough guess, if your interval is measuring as 0.392 seconds, the actual pellet travel time is going to be closer to 0.25 seconds. Especially considering that you say it goes right through 3/8" plywood (what sort? rough hem/fir/spruce sort of stuff? hardwood ply?) it seems unlikely your velocity is as low as you're calculating. probably closer to 700fps or more.


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PostPosted: Wed Apr 29, 2015 5:19 pm 
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GerardSamija wrote:
Probably a really obvious and stupid question, but... have you remembered to account for the fact that if the mic is at the muzzle location and you're recording the sound of the impact and measuring the difference between them... that the sound actually takes just as long to get back to the mic as it takes to get from the muzzle to the target? Not at all sure of the math needed to factor that in along with decreasing velocity of the pellet and other variables, but if you're taking the total duration of the sound as being the time it took for the pellet to get to the target then you're off by a LARGE factor. At a very rough guess, if your interval is measuring as 0.392 seconds, the actual pellet travel time is going to be closer to 0.25 seconds. Especially considering that you say it goes right through 3/8" plywood (what sort? rough hem/fir/spruce sort of stuff? hardwood ply?) it seems unlikely your velocity is as low as you're calculating. probably closer to 700fps or more.


Thanks, I indeed did take that into account if you read my original post...

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PostPosted: Wed Apr 29, 2015 5:26 pm 
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DigitalFx33 wrote:
Have you tried chronoconnect?
And do you have the short or long piston? My phantom with a lube and tune and plugged hole was shooting 660 with 14.3gr pellets.


Well, isn't THAT one sweet app! I measured out a 20 yard target, configed my settings, and according to Chrono Connect, I'm getting 740 fps. Woo hoo!

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PostPosted: Wed Apr 29, 2015 5:55 pm 
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Pretty speedy for a .22 cal Phantom, especially as an average over 20 yards....

Bob

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