Is there something I'm doing wrong here or did the chrono somehow misread the shot?
Everything I entered in the GGDT matches up fairly well with the conditions I had, and everything was measured with digital calipers and a digital scale. I couldn't figure out the exact chamber volume or pilot volume, but they didn't seem to make too much of a difference so I guessed what was closest.
I used a 54 caliber plastic sabot, and trimmed it as much as I could. It weighs 0.58 grams.
GGDT
Chrono reading
The plastic slug stopped at 40 pages. It punched a circle through the next 60 pages, and tore another 80 pages after that.
The gun
Assembled
An unrelated shot: 15.4 gram 4 inch nail at 220 psi with a 30 inch barrel. Book is 750 pages.
Both books are old and not being used anymore.
GGDT isn't showing the same velocities I get with a chrono
- MrCrowley
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I'm not sure if you have entered some the GGDT parameters correctly either. Though, I don't think they will change the output readings by much.
'Outer diam' should be the inside diameter of your chamber and 'Inner diam' should be 0 unless the cannon is a coaxial in which case it is the outside diameter of the barrel. For this cannon, inner diam. should be 0.
Valve coef. might be more accurate if it were in the 35%-50% range. I'm not really sure about this as I've never bothered to calculate the flow of a valve in terms of litres per minute with a drop of 1 bar in pressure, but I usually go for a number in that above range and other members seem to as well.
I think you should get chrony readings in the 800-1100fps range. You might get close to the SOS but I doubt you will get much higher than that.
'Outer diam' should be the inside diameter of your chamber and 'Inner diam' should be 0 unless the cannon is a coaxial in which case it is the outside diameter of the barrel. For this cannon, inner diam. should be 0.
Valve coef. might be more accurate if it were in the 35%-50% range. I'm not really sure about this as I've never bothered to calculate the flow of a valve in terms of litres per minute with a drop of 1 bar in pressure, but I usually go for a number in that above range and other members seem to as well.
I think you should get chrony readings in the 800-1100fps range. You might get close to the SOS but I doubt you will get much higher than that.
(^"air blast prior to projectile exit. " Picture by Technician1002. From unrelated thread. link)
I've had high readings shooting too closely to the chrono. As in the muzzle an inch before the first gate.
- jackssmirkingrevenge
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Holy enormous pictures batman!
[youtube][/youtube]
The above is a very small chamber at just 100 psi, filmed at 1000 frames per second you can see that the vapour released is substantial.
Is steam dense enough to set off the optical sensor in a fire alarm?Is water vapor really dense enough to trip the chrono's eyes?
[youtube][/youtube]
The above is a very small chamber at just 100 psi, filmed at 1000 frames per second you can see that the vapour released is substantial.
hectmarr wrote:You have to make many weapons, because this field is long and short life
^Nice video
I redid the shot with the muzzle 3 feet from the chrono's first sensor and hit 1102 fps.
Learned my lesson here.
Based on this shot and another with a lead ball, my flow coefficient is somewhere between 30-50%. What are other people using in GGDT for the flow coefficient of their barrel sealers?
I redid the shot with the muzzle 3 feet from the chrono's first sensor and hit 1102 fps.
Learned my lesson here.
Based on this shot and another with a lead ball, my flow coefficient is somewhere between 30-50%. What are other people using in GGDT for the flow coefficient of their barrel sealers?
- Technician1002
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A high speed camera and the rule in the background did provide good data on the projectile speed as well as the shockwave expanding before the projectile emerged. Much of the "Steam" in that shot is applesauce from a broken projectile apple. In broke on the way in, so we shot it anyway. Most shots don't have that much applesauce in the photos from an air cannon. The leading edge of the sauce is near Mach 1. It surprised me. The average bulk is about 2/3 Mach 1