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Author Topic: Home for a while  (Read 179 times)

Offline Dutch-Hunter

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Home for a while
« on: November 02, 2018, 11:50:15 AM »
Working on my probable last rifle project. My yearning to have a .243 pill leaving the muzzle at over 5000/fps. More about this later. While running the numbers I found an interesting elevation tid-bit. While doing a flight time analysis and trajectory tracking I found that the pill will slow to transonic speed at 2445 yards at 6000 feet in elevation. At sea level the transonic conversion is reached at 1970 yards.

Next question is how gravity affects the pill at various elevation change.
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Old enough to know better!
TO old to care!

Offline Madgomer

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Re: Home for a while
« Reply #1 on: November 02, 2018, 12:35:58 PM »
Sounds like a fun project DH - what is your current max muzzle velocity you've reached with the .243?   

Gravitational pull does decrease with altitude, but it's pretty slight within the realm of where we'd be shooting without the aid of a breathing apparatus.  If I did my math right, between sea level and 6000 feet you'd see about a 0.06% (six one hundredths of a percent) change in gravitational pull on the pill - I arrived at that by just doing a ratio of earth's radius squared and the radius at 6000 feet above sea level squared.  Sorry, couldn't help myself.

Based on the link below you might have more variation in gravity based on latitude than on altitude.
http://curious.astro.cornell.edu/about-us/42-our-solar-system/the-earth/gravity/93-does-gravity-vary-across-the-surface-of-the-earth-intermediate
One of God's greatest gifts to us is
the great outdoors - get out there
and enjoy it!

Offline Dutch-Hunter

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  • Location: Dunn County, Wisconsin, US
  • Doin' what I love!
Re: Home for a while
« Reply #2 on: November 02, 2018, 12:58:39 PM »
Hi Mad, Presently the highest 243 muzzle velocities for the pill weight I have are the 243 Catbird pushing a 95 gr pill at 3575 fps, and a 243WSSM pushing a 90gr at 3325.

The muzzle velocity that I'm plugging into the equations is 5150. Like any build it must be built around a projectile. I have found a monolithic 90gr with a coefficient of .510. Have to use monolithic because of rational failure of frangible pills. I'm still playing with numbers. So far it looks like I'll need a 1:14.5 twist rate to achieve a stability factor of 1.52. This puts the rotational pill speed at 248,300 and is why the frangible pills will not work. The monolithic pill maker "believes" the one I'm going to use "should" hold together.

Now I'm waiting to talk to the barrel manufactures.

The gravitation pull is very minor compared to the coriolus effect at ranges beyond 1500. Then direction of flight must be taken into account.
Gun Geek! Proud of it!
Old enough to know better!
TO old to care!

Offline Hunt Master

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Re: Home for a while
« Reply #3 on: November 05, 2018, 05:02:57 AM »
Wow... and when I look at the Matrix all I see is blond, brunette, redhead...
If you can't be hunting....  Be here...  --9-8-7
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