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Drag Function question.

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Unread 05-22-2009, 06:54 AM
JBM JBM is offline
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Join Date: Jan 2004
Location: New Mexico
Posts: 113
Re: Drag Function question.

Originally Posted by Bullet bumper View Post
JBM Said ,
" My MPM program doesn't use drag functions at all except in output" .

Then can you explain to me please why your Modified Point Mass program has an input entry for the specific drag function ?
Because it lists the BC on output in the coefficients section. It can't do that without know what drag function to calculate the BC for.

(This is an old thread!)

JBM Small Arms Ballistics --
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Unread 05-22-2009, 07:23 AM
Platinum Member
Join Date: Jan 2004
Location: Blackfoot, Idaho
Posts: 8,826
Re: Drag Function question.

JBM, Thanks for awakening the "old thread"......

Good read.

Sorry I don't understand one iota of the technical jargon but appreciate the results.

You're doing a good work.

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Unread 06-08-2009, 01:39 PM
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Join Date: Aug 2005
Location: Murray, Ky.
Posts: 1,285
Re: Drag Function question.

Hey guys I know this is an older post but I was shooting with some friends of mine this weekend and we had a discussion about this very thing. I was shooting my 338 edge with 300 gr smks running right at 2917 fps. My balistic program that I use sugested that I use the g5 model and it was dead on out to 600 yds that's as far as we can shoot right now. They were shooting anything from 22-250 to 6.5-284, using berger vld's and smk's but they had to use the g1 drag model the g5 had them shooting way low. Why would the g5 be right on for me and so low on there's .

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Unread 06-09-2009, 05:17 PM
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Join Date: Jan 2009
Location: Oregon
Posts: 18
Re: Drag Function question.


For those distances/cartridges I would not expect different drag curves to produce significantly different results.

For instance, here are some results of one of my 6.5x284 loads, comparing
1. Using Sierra provided multiple G1 BC/velocity values
2. Using just top Sierra G1 BC value (0.595)
3. Using top Sierra G1 BC value converted to G5 BC with G5 drag curve
4. Using top Sierra G1 BC value converted to G7 BC with G7 drag curve

2775 fps Sierra 142gr MK, sight Height 1.8. ICAO standard conditions.

This is generated with some software I wrote, but you could easily compare with any of the other packages out there.

Drop (in) 600 yd 1000 yd
1. Multi-G1 -82.2 -322.3
2. G1 -81.4 -314.7
3. G5 -82.0 -321.5
4. G7 -81.5 -316.2

I would suggest using the Sierra multi-BC values where you have them with the G1 curve. If you have a vendor supplied or measured BC for another drag curve then use that. Converting a G1 BC to another drag curve is just another place to introduce some error, since most of the time you don't know the velocity range over which the G1 was calculated.

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