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GGDT accuracy with bb's

A place to ask general spud cannon related questions.
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GGDT accuracy with bb's

Unread postAuthor: Gun Freak » Mon Mar 29, 2010 8:05 pm

How accurate is GGDT with shooting airsoft bb's out of pneumatics? Or any cannon? I am getting unusually high velocities (521 fps on only 29 psi, and 993 fps on 120 psi). I used barrel sealing (co-ax). Thanks

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Unread postAuthor: DYI » Mon Mar 29, 2010 8:42 pm

You'll likely notice some trans-sonic flow effects that reduce efficiency as you approach the SOS in air. They're more problematic at low pressures where you may see steep drop-offs in efficiency above 600fps or so, but they're present regardless of pressure. 993fps at 120psi seems unreasonably high based on my experience, but 521 fps at 29 psi does not.

As far as I know, SOS and particle speed effects are not accounted for (or not very well accounted for, at least) in GGDT, so take any velocities nearing or above SOS with several grains of salt, especially at low pressures.
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Unread postAuthor: Gun Freak » Mon Mar 29, 2010 8:50 pm

Thanks.
message too short
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