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Old January 12, 2002, 03:21 PM   #1
Peter M. Eick
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Are large differences in SD between guns common?

I was out shooting 9mm a few days back and I noticed with the same run of reloads the following averages for standard deviation for different pistols:

Sig 210-6 average sd 12 fps
Hk p7psp1 average sd 33 fps
Hk p7psp2 average sd 23 fps
Hk p7 average sd 19 fps

These are all with the same reload run (berry 115 rn with 6.0 grns power pistol, starline brass, cci500 primers). All measurements were from 20 shot strings at about 10 feet with a 35p chrono.

I was expecting some small variations say 2 to 5 fps, not that big. Also I did notice that each guns velocities were very consistent, ie: the high and low and average were very close.

Any insights?
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Old January 12, 2002, 07:33 PM   #2
kurt IA.
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I would say that yours were normal, Each gun is a law unto ti's self, what shoots great in one may not in another, even the same make and model.
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Old January 12, 2002, 08:22 PM   #3
C.R.Sam
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I'd say your four were unusually close for a random pick of four different guns. Easy to get greater spread from two identical guns.

Like Kurt said, each is different critter.

Sam
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Old January 13, 2002, 02:15 AM   #4
WESHOOT2
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".....but NOT always....."

This quote comes from a Speer Manual (#12?). There's an article along with it about the same load in four specimens of the same gun; variation in velocities -- over 200fps.

I use a few matching pairs for ammo testing; ALL GUNS ARE ALWAYS DIFFERENT (and I still remember the time a friend finished a new 6" 1911, brought it over for chrono testing, and found it significantly slower-shooting than his 5").

Just read an article of discovery, where the shooter found his higher-deviation load more accurate than his low-SD ammo.

"Testing required"; all the rest is guessing...................
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Old August 19, 2002, 01:43 AM   #5
kidcoltoutlaw
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sd ? for weshoot2 or anybody else

what is a good sd .have you ever loaded with the chronograph to get a low sd.then shot it on paper to see what it would do .if so did it work.esp with a rifle for long range work,thanks,keith
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Old August 19, 2002, 06:56 AM   #6
bfoster
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Peter,

You may find the sd's fall in a different order if the load is changed: bullet weight, powder, and primers all factor into producing low variabilities.

But as weshoot2 mentions, loads with the lowest sd's dont always shoot best, many benchrest riflemen have observed this.

Bob
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Old August 19, 2002, 08:13 PM   #7
WESHOOT2
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THERE ARE NO GOOD NUMBERS

Paper? or meat?

If paper (target) only, then the only numbers that might matter are a Power Factor like IPSC or IDPA, and the measure of your impacts.

If meat, terminal performance is based on the number, so low deviations are required to confirm correct bullet performance.

I test both ways.

I don't know nuthin' about long guns; I'm a rifle "Frosty".


Don't get hung up on numbers, because what really matters is usually accuracy first, and for meat-shooters low deviations second.
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