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Posted: 5/15/2008 3:59:00 PM EDT
| what is the specific gravity of the M193 ball ammo? |
It's lower than the generally used figure of 10.7 to 10.9 for jacketed lead bullets. Hornady 55 grain FMJ/BT bullets and IMI M193 bullets have a specific gravity of 10.2. (Technically speaking, specific gravity is a unit-less figure, becuase the units cancel when dividing.) |
It's necessary for accurate barrel twist rate/gyroscopic stability calculations. |
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thanks for the SG info. is there like some guide online about different types of bullets and their respective SG's? the reason for the specific gravity question was to calculate the proper twist rate of a give rifle for a bullet. twist rate = ((180*calibar^2)/length)*(specific gravity/10.9)^.5 |
That's hellish with normal calculators: It's a good thing I have my Ti-86 in that mag pouch on my stock... What, no one else does that? |
When I was in high school, after walking to school in the snow ( quite an accomplishment in southern california ... ), we used slide rules and we liked it. |
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I would have used the term "density" and made it clear I was talking about the bullet itself. My first thought when reading the title was "is the guy looking to find out how much a particular number of rounds will weigh, or how many he can fit in a given volume?" Bullet density makes a lot of sense, but I always think of chemical solutions first when someone mentions "specific gravity." Maybe it's just my background... Is SG the more common method of describing this bullet feature? By the way, density and specific gravity are not identical: as noted, specific gravity is a unitless quantity while density is in grams per milliliter (or other mass per volume) units. In this application, they could both serve the same purpose. |
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well that sucks. just in typical fashion when you are really really wanting to know something on the net, there isn't an answer. i guess the only way to know is to dismantle various bullets, and take their measurements. i guess its safe to assume that most FMJ .223 rounds have a SG of 10.2. well for you guys that have 1:9 twists in your rifles a good bullet of choice would be the real NATOs; the green tips 62 gr for you other guys with 1:12 twists, the 55 gr bullet with the NATO powder loading or just a 55 gr FMJ bullet. |
If there were a very simple (and not terribly messy) method of measuring the volume of a bullet, calculating the SG would be trivial. As it is, you need a very precise graduated cylinder to get the volume of a .224" diameter bullet, and the wet-measurement process is not "mess-free." It's doable, but it's a pain. |
Ok, this is the second horribly nerdy thing I'll add to this thread: I have OODLES of graduated cylinders, beakers, and test tubes sitting idle after I sold my Bunsen burner. I might just calculate the average density of various projectiles when I get some time. Edit: And I'd like to add, no I did not have a meth lab. |
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I lernd to sypher usin' ma fin'gers an tows......wa's herder sprcilly sins I don lost ma tow one winner dew to foss. Winner in Ha'wae is tuff.  Aloha, Mark |
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it got to thinking. you know the mass of the bullet and the graduated cylinder,so put the bullet in a graduated cylinder, fill the graduated cylinder up to the 10 mL mark, and weigh the graduated cylinder with the bullet and the water in it. with this mass you just got subtract the mass of both the bullet and graduated cylinder. doing this will give you the mass of the water which will be less than 10 g (we will call this mass X). now that we have X, do this fomula 10-X=A. A will by in grams but not to worry we can convert it to mL's. since water density is 1 g/mL, we can use this to convert the mass of A to mL. A is the volume of the bullet. sounds weird but will work and simple than explaining it |
Kind of late to pick the twist rate after the barrel is on the gun. That's a kindergarten math problem. |
It's an easy problem, just not easy to type in on cheapo calculators. |
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That is a very simplified form of the stability equation that doesn't take into account the weight distribution of the bullet. Much more complex formulas exist for calculating gyroscopic stability which should typically be 1.5 for most applications. http://www.nennstiel-ruprecht.de/bullfly/gyrocond.htm#header Online calculators exist that requre specifics of bullet geometry to get more accurate results. http://www.riflebarrels.com/products/software.htm http://www.riflebarrels.com/articles/bullets_ballastics/bullet_design.htm I have been working on some solid copper turned bullet designs for my personal use and have used these extensively. The results for calculated BCs and stability seem to agree well with data from barnes bullets. |
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