Are large differences in SD between guns common?

Peter M. Eick · January 12, 2002, 03:21 PM

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?

kurt IA. · January 12, 2002, 07:33 PM

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.

C.R.Sam · January 12, 2002, 08:22 PM

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

WESHOOT2 · January 13, 2002, 02:15 AM

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...................

kidcoltoutlaw · August 19, 2002, 01:43 AM

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

bfoster · August 19, 2002, 06:56 AM

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

WESHOOT2 · August 19, 2002, 08:13 PM

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.

January 13, 2002, 02:15 AM	#4
WESHOOT2 Senior Member Join Date: February 20, 1999 Location: home on the range; Vermont (Caspian country) Posts: 14,324	".....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................... __________________ . "all my ammo is mostly retired factory ammo"

August 19, 2002, 01:43 AM	#5
kidcoltoutlaw Senior Member Join Date: April 13, 2000 Location: bluefield Posts: 735	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 __________________ It's not just a gun it's the symbol of freedom

August 19, 2002, 08:13 PM	#7
WESHOOT2 Senior Member Join Date: February 20, 1999 Location: home on the range; Vermont (Caspian country) Posts: 14,324	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. __________________ . "all my ammo is mostly retired factory ammo"

January 12, 2002, 03:21 PM	#1
Peter M. Eick Senior Member Join Date: August 3, 1999 Location: Houston, Texas Posts: 2,991	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? __________________ 10mm and 357sig, the best things to come along since the 38 super!

January 12, 2002, 07:33 PM	#2
kurt IA. Senior Member Join Date: February 19, 2001 Location: Iowa Posts: 141	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.

January 12, 2002, 08:22 PM	#3
C.R.Sam Senior Member Join Date: October 29, 1999 Location: Dewey, AZ Posts: 12,858	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

August 19, 2002, 06:56 AM	#6
bfoster Senior Member Join Date: October 13, 1998 Location: N. of Fords Switch, OK, USA Posts: 297	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