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Old April 1, 2008, 03:29 PM   #1
hillbille
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help bp guys

heres one to scratch your head on. my son is in the pinewood derby thing, those wooden little cars, anyway the car can only weigh 200 grams, I was going to use 490 round balls I made for my 50 cal.. thing is how many grains(490gr) is there in a gram. I'm going to drill hole in the wood to put balls in what I need to know is how many balls to add. bottom line is how many grams does a 490 round ball weigh?
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Old April 1, 2008, 03:53 PM   #2
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15.43 grains per gram

490 grains = 31.75 grams
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Old April 1, 2008, 04:01 PM   #3
hillbille
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grymster one more please, is a 490 ball 490grains or 490 cal.?
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Old April 1, 2008, 04:18 PM   #4
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A .490 ball is 0.490 inches in diameter, or 49 caliber. Pure lead weighs 11.34 grams/cubic centimeter. The volume of a round ball 0.490 inches in diameter is 8.0756 cubic centimeters. Thus a .490 round ball weighs 91.58 grams. I think.
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Old April 1, 2008, 04:22 PM   #5
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Old April 1, 2008, 04:25 PM   #6
Jim Dandy
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Quote:
Originally Posted by mykeal
Pure lead weighs 11.34 grams/cubic centimeter.
No, the DENSITY of lead is approximately 11.34 g/cm^3.

Quote:
Originally Posted by mykeal
The volume of a round ball 0.490 inches in diameter is 8.0756 cubic centimeters. Thus a .490 round ball weighs 91.58 grams.
No, the volume of a 0.490" round ball -- (4*PI*r^3)/3 -- is 0.061600872 cubic inches. This is equal to 1.009457431919808 cubic centimeters. We'll call it approximately 1 cubic centimeter for this application.

A sphere with a volume of 1.0 cubic centimeter and a density of 11.34 grams per cubic centimeter has a mass of 11.34 grams. (Weight is about 0.11 Newtons.) This works out to about 0.025 pounds or 0.40 ounces or 175 grains. Check your scale and see.
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Old April 1, 2008, 04:32 PM   #7
hillbille
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mykeal don't know where you got that but thanks for the info I was going to go with about 7-9 but with what you say it is closer to 2. but thanks for the quick response and answers.
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Old April 1, 2008, 04:42 PM   #8
grymster2007
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volume of 1.2246 cm sphere = 1.0095 cm3

specific gravity cast lead = 11.35

11.35 * 1.0095 = 11.457 grams

11.457 grams * 15.43 = 177 grains

I think!

Jim Dandy gave the answer while my pea brain was still smoking through the question!
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Last edited by grymster2007; April 1, 2008 at 04:43 PM. Reason: slow
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Old April 1, 2008, 04:45 PM   #9
Jim Dandy
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Quote:
Originally Posted by hillbille
mykeal don't know where you got that but thanks for the info I was going to go with about 7-9 but with what you say it is closer to 2.
Uh, you better check those numbers again. The figures grymster2007 and I have provided are consistent with what Speer says their 0.490" round balls weigh: http://www.speer-bullets.com/default...1=3&s2=7&s3=23
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Old April 1, 2008, 05:30 PM   #10
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Jim Dandy and grymster2007 are right.

It is density (I knew that; my fingers didn't), and I still can't figure out how I got that first number. Pushed the wrong button somewhere.
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Old April 1, 2008, 05:34 PM   #11
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Old April 1, 2008, 05:37 PM   #12
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Old April 1, 2008, 06:17 PM   #13
hillbille
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ok so you are saying it is roughly11 1/2 grams, per 490 ball. which is back to the 7-10 range with the wood.
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Old April 1, 2008, 07:49 PM   #14
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Quote:
Originally Posted by mykeal
Jim Dandy and grymster2007 are right.

It is density (I knew that; my fingers didn't), and I still can't figure out how I got that first number. Pushed the wrong button somewhere.
We all have our moments. Hell, I had to figure and refigure to make up my mind I was right.
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Old April 1, 2008, 07:51 PM   #15
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Quote:
Originally Posted by hillbille
ok so you are saying it is roughly11 1/2 grams, per 490 ball. which is back to the 7-10 range with the wood.
Yes, the 0.490" balls are roughly 11.5 grams. However, you didn't state what the wood weighs.
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Old April 1, 2008, 08:10 PM   #16
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FYI:

I just went and weighed five (5) Hornady 0.490" balls on my Pact electronic scale; 178 grains, 177.2 grains, 177.6 grains, 177.5 grains, and 177.2 grains. This works out to an average weight of 177.5 grains or 0.025357142 pounds. My calculator says this is equivalent to 0.011501806 kg -- 11.5 grams.
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Old April 2, 2008, 04:13 PM   #17
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Before I could remember the formula for volume of a sphere (4/3piRcubed), I used a rough approximation of 52.5% of the volume of a cube with a side length the same as the sphere diameter. Don't really know how I could remember that and not the simple formula!!!

So how's the car coming hillbille?
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Old April 2, 2008, 05:46 PM   #18
hillbille
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six and one half balls put us just over weight. The balls took up to much space I drilled a 1/2 inch hole which the 490 ball just fit in but we could only get3-3 1/2 balls in, so I melted them poured them down the hole got not quite 6 1/2 in melted. all we need is paint then weigh it again with wheels and all on, if we are over i figured i could drill a small bit of lead out of hole. He has lost 2 years running but I let him do almost all the building and sanding, painting ect. some of these cars you can tell the parents did it all I know the kids probubly were'nt even in the same room. I think he has more fun building than winning, and thats what its all about, he is a good loser, something hard to come by in kids anymore. thanks for all the help from everyone.
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Old April 3, 2008, 12:28 AM   #19
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I remember when we built our pinewood derby car, there was a package of 2 pre-cast weights that were sold separately as an option for the car kit. I think that we had to drill the holes so we could choose where to place them. These weights were a little larger in diameter than a pencil and maybe 2 inches or so long, and they were designed to just epoxy in while keeping the car under the weight limit.
We ended up putting powdered graphite on the axles which really helped!
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Old April 4, 2008, 08:17 PM   #20
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i remeber that when i was a kid. use to use graphite on the wheels worked really good.
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Old April 5, 2008, 12:18 AM   #21
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polished the nails used for axles, kept working graphite into wheel by spinning each wheel on axle while pouring on graphite, smoothing out all the rough edges. just think hillbille , in a few years that boy will be tuning up your guns
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