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Standard deviation vs. spread on velocities (Read 21635 times)

JLouis Frequent Elocutionist Offline Posts: 10625 Joined: Apr 8^th, 2009	Re: Standard deviation vs. spread on velocities Reply #60 - Nov 4^th, 2018 at 6:24pm	Print Post
	Pretty much grasped it at the beginning of your last post and what I apparently missed Dellet or just simply went over my head at the time. I am not sure where the one good group came from it was several over that long period of time working up to my personal goal. The best .190 but really meaningless with the exception of it helping the 5-5 shot group average on that specific practice target and really of no other value to me at the time or even now.

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Dellet Frequent Elocutionist Online Posts: 1303 Joined: May 19^th, 2017	Re: Standard deviation vs. spread on velocities Reply #61 - Nov 4^th, 2018 at 6:52pm	Print Post
	This really is not all that difficult. BC is a number based on time of flight, reduction in speed over time, and drop over distance. This all happens outside the barrel. Your ES will be determined inside the barrel. Your very own numbers on the print out show that the vertical spread expected would be about .220”-.225” based on an ES of 15fps. 1510-1525 fps. That is with both a G1 of .400 and .420. The farther you move the target back. The more those inconsistencies will matter. Those numbers may change as I took an educated guess at your bullet length and used 1.175”


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JLouis Frequent Elocutionist Offline Posts: 10625 Joined: Apr 8^th, 2009	Re: Standard deviation vs. spread on velocities Reply #62 - Nov 4^th, 2018 at 7:59pm	Print Post
	Agree Dellet probably boring to some and maybe a bit interesting to others. I tend to think it informative to share the data for those who tend to think their BC always remains the same as well as everything else of which it never does. Just recently someone shared some data and it showed the BC changed ten times on the printout yet stated it always remained the same so it can get a bit a confusing for some or just plain boring and meaningless to others and thanks for your own input I appreciated it.

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JLouis Frequent Elocutionist Offline Posts: 10625 Joined: Apr 8^th, 2009	Re: Standard deviation vs. spread on velocities Reply #63 - Nov 4^th, 2018 at 8:14pm	Print Post
	That is correct the bullet I ended up using was .963 in length, 1-16 alloy, around 195grs and a Darr cylindrical Flat Nose bullet. The barrel twist rate was 1-15 and the data shown was for one of the five bullet designs I was testing to derive at the most consistent design for the intended purpose. The load used ended up being 13.9 grs. of 300MP and the primers the same as is noted on the printout. I sure do wish we could finally get off the entire record subject but I also wanted to clarify what ended up being used. JLouis
	« Last Edit: Nov 4^th, 2018 at 8:48pm by JLouis »
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Dellet Frequent Elocutionist Online Posts: 1303 Joined: May 19^th, 2017	Re: Standard deviation vs. spread on velocities Reply #64 - Nov 4^th, 2018 at 8:21pm	Print Post
	Using the length of 1.165” from Frank the numbers of the spread don’t change much. But to try to tie all this in for the OP, using Franks bullet and the numbers off JL’s printout. Dominik was shooting around 1150-1300 fps. In theory the best case scenario with an ES of 50 1150/1200fps. That would make it hard to have less than 1” vertical spread. Something else that is not helping him, is he is shooting at possibly the worst velocity window, hard to pick a speed where there’s is more turbulence.


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Dellet Frequent Elocutionist Online Posts: 1303 Joined: May 19^th, 2017	Re: Standard deviation vs. spread on velocities Reply #65 - Nov 4^th, 2018 at 8:54pm	Print Post
	frnkeore wrote on Nov 4^th, 2018 at 8:38pm: Why not post that print out? Dellet, Actually, for 200 yard shooting, the most used velocity (1450 fps), in our sport, is the worst for wind drift. A short, flat nosed 1175 fps bullet, will get below the speed of sound, before 200 yards and possibly increase it's BC in the process. A 1450 fps bullet, usually stays supersonic to 200 yards, loosing more of a percentage of the starting velocity, giving more wind drift. If it's a flat nosed, low BC bullet, it can get into the transonic range, causing tipping, from the buffeting. Frank I will admit to being on the low end of the learning curve there with cast bullet shape. But the OP started at 1150 and worked up. For finding pressure limits and general load info it makes perfect sense. Or looking for a bullet that buffers the transition speeds well. I don’t think I would choose to shoot for maximum accuracy in the 12-1400 MV window. Or are there specific designs that work well there?


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frnkeore Frequent Elocutionist Offline Posts: 7659 Location: Central Point, OR 97502 Joined: Jun 16^th, 2010	Re: Standard deviation vs. spread on velocities Reply #66 - Nov 4^th, 2018 at 9:15pm	Print Post
	The only design that sheds the least velocity, at supersonic speeds, is the spitzer. Above SS speeds, you have to penetrate the shock wave (sharper point the better) and it takes a lot of power, to do so. Below SS, you need laminar flow to reduce drag and it takes less power to get to the target, because, it's not pushing the shock wave. Sharpe points, aren't as effective at subsonic speeds. The air needs to flow around the point, at sub speeds. Frank

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