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All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here! |
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08-30-2017, 10:02 AM | #1 |
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weight of SS spears
i need the weight per inch for 9mm and 10 mm spears in grams.
anybody know? I know 7mm weigh 8.24grams per inch 7.5mm= 9.12 grams and 8mm is just under 10 grams per inch I'm not sure if it just scales up - or if it's exponential easier just to weigh a spear and divide it by number of inches if it just scales up - then it would be 1.78(ish) per gram increase per mm increase in diameter . so 9 mm should be 11.8 g per inch and 10 mm 13.6 g per inch - anyone know it for any of these larger diameters?
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08-30-2017, 10:57 AM | #2 |
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Re: weight of SS spears
Do you want 9mm? or 11/32" and 3/8"
A 61" 11/32" Shaft weighs 720grams
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08-30-2017, 11:17 AM | #3 |
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Re: weight of SS spears
you have to use area of circle to calculate...
7mm = 38.48 sq.mm @ 8.24g = 0.214g per sq.mm 7.5mm = 44.18 sq.mm @ 9.12g = 0.207g per sq.mm 8mm = 50.27 sq.mm @ 10g = 0.199g per sq.mm assume average to be 0.21 grams per inch 9mm = 63.62 sq.mm x 0.21 = 13.36 g per inch 10mm = 78.54 sq.mm x 0.21 = 16.49g per inch |
08-30-2017, 11:26 AM | #4 |
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Re: weight of SS spears
Jason, the best advice is just to go out and get a big Water trough from your local Agricultural supply store. Get some Salt. Get a Hydrometer. Phil H. gave me that advice a long time ago. There's a ballast tank next to my sanding table.
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08-30-2017, 12:42 PM | #5 |
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Re: weight of SS spears
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08-30-2017, 02:04 PM | #6 |
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Re: weight of SS spears
Yeah, just use an online calculator, I've done that ballasting my airguns and they get you super close. If you want the weight in fresh water, you subtract the volume in cm3 from the total mass.
Let's say you have a 8mm x 160cm spear. It will weigh close to 630g. But it will also have a volume of 80cm3, so the spear will "weigh" (630-80) 550g in fresh water. And I guess about 2.5% less in salt water. (As always, there are smarter math guys than me out there, so if I am wrong please do correct me). |
08-30-2017, 05:46 PM | #7 |
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Re: weight of SS spears
I Love it...But how do you compensate for the reduced area of the point, and the increase for loading fins, or the decrease for loading notches...OH..and how about the flopper and pin..or two..and then there is the trigger loading notch/'s, !?
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08-30-2017, 06:33 PM | #8 | |
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Re: weight of SS spears
Quote:
Come on, Seatux. Jason asked a very specific, some would say overly so, question and some of us indulged him. Please allow us to do so I know 80cm3 of buoyancy makes zero real life difference but being nothing wrong with the exercise The exercise is actually the same for building a whole gun. I have seen people try to do the math upfront but forget that all parts of the gun, even the negative ones, still displace water and thus increase buoyancy. Last edited by Diving Gecko; 08-30-2017 at 07:04 PM. |
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08-30-2017, 07:25 PM | #9 |
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Re: weight of SS spears
I said I loved it!
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08-31-2017, 12:04 AM | #10 |
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Re: weight of SS spears
I have it long time back get it from a forum ,hope it will help
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08-31-2017, 08:16 AM | #11 |
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Re: weight of SS spears
Seatux the answer to your question is the Ballast Tank.
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08-31-2017, 09:38 AM | #12 |
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08-31-2017, 01:16 PM | #13 |
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Re: weight of SS spears
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09-04-2017, 07:55 AM | #14 | |
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Re: weight of SS spears
Quote:
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09-04-2017, 07:59 AM | #15 |
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Re: weight of SS spears
Jason, this is all only part of the puzzle. Even if you know exactly how much weight to add.. you still don't know where to add it.
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