Author Topic: What is "SD" in relation to handloading  (Read 228 times)

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Offline Grendel

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What is "SD" in relation to handloading
« on: March 22, 2019, 07:58:26 PM »
Noob question: What's 'SD'?
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Offline eastman

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Re: What is "SD" in relation to handloading
« Reply #1 on: March 22, 2019, 08:36:23 PM »
Noob question: What's 'SD'?

Standard Deviation
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Offline Grendel

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Re: What is "SD" in relation to handloading
« Reply #2 on: March 22, 2019, 09:43:02 PM »
Noob question: What's 'SD'?

Standard Deviation

Thanks. And how is that used or relevant in this context?
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Offline Boris_LA

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Re: What is "SD" in relation to handloading
« Reply #3 on: March 23, 2019, 12:26:34 AM »
Noob question: What's 'SD'?

Standard Deviation

Thanks. And how is that used or relevant in this context?
Smaller SD indicate better consistency and less velocity spread shot to shot. That leads to better accuracy potential and tighter group. Smaller SD is one of the desired indicators. SD less than 20 is good, single digits is excellent. Another valuable statistical number is ES - Extreme spread. Smaller is better.

Offline Grendel

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Re: What is "SD" in relation to handloading
« Reply #4 on: March 23, 2019, 07:02:23 AM »
How does one go about calculating the SD of a given load? Is the difference between what you get velocity wise and what the book says you should get or something different?
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Offline painter

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Re: What is "SD" in relation to handloading
« Reply #5 on: March 23, 2019, 07:29:08 AM »
It only applies to the group of rounds fired over the chronograph. Has nothing to do with the load data.
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Offline Grendel

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Re: What is "SD" in relation to handloading
« Reply #6 on: March 23, 2019, 08:30:08 AM »
Thanks.
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Offline Chuck in Indiana

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Re: What is "SD" in relation to handloading
« Reply #7 on: March 23, 2019, 09:01:44 AM »
Where's that popcorn emoticon?  :) A couple of days ago, I loaded some Berrys 124 HBRN with 4.2, 4.4, and 4.6 of N330 @1.142". I don't have a chrono, though.. I'll probably just pick the one I like. Maybe I can get out today.. the weather has forgotten how to stop blowing.
« Last Edit: March 23, 2019, 09:42:57 AM by Chuck in Indiana »

Offline Boris_LA

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Re: What is "SD" in relation to handloading
« Reply #8 on: March 23, 2019, 05:43:36 PM »
To make it clear, SD and ES are attributes of ammo consistency and indicate a good loading technique/components with less variables.
Its not always directly translate to the ammo/barrel downrange accuracy. Very consistent ammo in the particular barrel loaded to the wrong average velocity, may make a larger group than slightly less consistent ammo, but with velocity optimized for given barrel.
Correctly optimized for your barrel velocity AND a consistent ammo with low SD and ES = ultimate goal.

Offline 1SOW

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Re: What is "SD" in relation to handloading
« Reply #9 on: March 23, 2019, 09:05:26 PM »
What Boris said!
Sometimes the ammo with other than the "best" numbers  won't give the best results. :-\

Offline Grendel

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Re: What is "SD" in relation to handloading
« Reply #10 on: March 23, 2019, 10:08:34 PM »
I asked this in my own thread, but never got an answer: My Lyman manual has the abbreviation(s) SD & BC under a picture of the bullet. What's that all about?

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Online tdogg

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Re: What is "SD" in relation to handloading
« Reply #11 on: March 23, 2019, 10:25:07 PM »
That's describing the bullet's sectional density and ballistic coefficient.

Not really needed for Pistol loading but both are used to characterize in flight performance.

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Offline Grendel

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Re: What is "SD" in relation to handloading
« Reply #12 on: March 23, 2019, 10:28:33 PM »
That's describing the bullet's sectional density and ballistic coefficient.

Not really needed for Pistol loading but both are used to characterize in flight performance.

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Tiny

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Thanks! But: what's it mean? is bigger better, or smaller sweeter?
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Offline Boris_LA

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Re: What is "SD" in relation to handloading
« Reply #13 on: March 23, 2019, 11:23:33 PM »
Sectional density is pure bullet material/build characteristic like hardness in the lead cast bullets. The important for pistol ammo reloading is only the external material (Jacketed, Plated, Lead) and shape/size. No good/bad SD numbers.
Ballistic coefficient is related to shape/weight of the bullet and how the shape affects the flight and loss of the velocity and energy down range. Larger is better as it provide less vertical drop on the distance. Boattail long rifle bullets have better BC and don't loose their energy as fast  as low BC airgun diabolo-shaped pellets with high drag. Pistol bullets not much better and generally have low BC.
External ballistics that calculated using BC is not part of your general pistol reloading tasks. Its only for your information.
Useful information in the manual is the reported tested powder charge (min-max) and achieved velocity at the OAL they used for testing.
You can safely start with their min reported charge and compare your velocity results to their to see how much your barrel is different from testers and if you are in the same velocity range.

Online tdogg

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Re: What is "SD" in relation to handloading
« Reply #14 on: March 24, 2019, 01:52:01 AM »
Sectional density is the bullet weight divided by the cross sectional area.  A larger number indicates it carries more energy while travelling.  Meaning it has more knockdown power and is less affected by the wind.

Ballistic Coefficient is a metric to characterize how much drag/energy loss a bullet encounters during flight.  The larger number indicates that the bullet will carry a flatter trajectory or will have less bullet drop at distance.

Neither of these practically matter at normal pistol distances.  If you start shooting pistols like Joe L, then you might start needing to pay attention to these metrics!

I'm not a ballistician and no I didn't stay at a Holiday Inn last night :).

Cheers,
Toby

 

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