Ammunition & Hand Loading > Cartridge and Shotshell reloading

Pistol Standard Deviation

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SemperFiGuy:
A variance in muzzle velocity should have little or no effect on lateral [side-to-side] point of impact.

If velocity variance has any effect on POI at all, it will most likely show up in vertical POI variance.   However, in the case of a handgun at 25 yards, POI variances due solely to velocity variances are probably not even measurable.

Some of the factors which affect variations in muzzle velocity are
variations in:
>primer brand [unless all ammo is loaded w/same primer batch]
>primer flash hole diameter
>cartridge case headstamps [different manufacturers]
>case cleaning
>bullet weights  [weigh your bullets to 0.1gr and see what you find]
>bullet seating depth
>powder charge [unless each load is weighed to 0.1gr]
>bullet seating depth
>bullet crimping
>barrel warp under heating
It's almost impossible to separate the effect of these different variables on velocity variance.

Now, a 30ft/second SD for muzzle velocity means that the entire population of your shots experiences a variance range of 180ft/second.

Example:   Assume standard distribution and an average MV of 1000ft/sec.   Then the velocity range for all shots would be 910-1090ft/sec, with an occasional flyer above or below this range.

Which is a pretty hefty variation, but probably other factors [trigger pull, etc.] would have more effect on POI.

Final Analysis:   The primary purpose of a handgun is personal protection.   What shows on your target will work for you.   Just fine.

sfg

OnTheFly:

--- Quote from: OnTheFly on June 13, 2013, 06:47:01 PM ---My reloading friend chrono'd some commercial ammo and he said the SD was much lower. Waiting to hear back from him on how low that number was.

Fly

--- End quote ---

I misspoke.  He only looked at the data on commercial ammo.

Fly

OnTheFly:

--- Quote from: abbafandr on June 13, 2013, 06:57:26 PM ---Reloading, shooting and statistics :o  May I be excused, Mr Fly, my brain is full :laugh:

--- End quote ---

Ok...I must admit that I am a little bit of a CDO math geek.  Maybe not as much as JTH, but more than most.   ;D

Fly

OnTheFly:

--- Quote from: SemperFiGuy on June 13, 2013, 09:13:05 PM ---A variance in muzzle velocity should have little or no effect on lateral [side-to-side] point of impact.

If velocity variance has any effect on POI at all, it will most likely show up in vertical POI variance.   However, in the case of a handgun at 25 yards, POI variances due solely to velocity variances are probably not even measurable.

Some of the factors which affect variations in muzzle velocity are
variations in:
>primer brand [unless all ammo is loaded w/same primer batch]
>primer flash hole diameter
>cartridge case headstamps [different manufacturers]
>case cleaning
>bullet weights  [weigh your bullets to 0.1gr and see what you find]
>bullet seating depth
>powder charge [unless each load is weighed to 0.1gr]
>bullet seating depth
>bullet crimping
>barrel warp under heating
It's almost impossible to separate the effect of these different variables on velocity variance.

Now, a 30ft/second SD for muzzle velocity means that the entire population of your shots experiences a variance range of 180ft/second.

Example:   Assume standard distribution and an average MV of 1000ft/sec.   Then the velocity range for all shots would be 910-1090ft/sec, with an occasional flyer above or below this range.

Which is a pretty hefty variation, but probably other factors [trigger pull, etc.] would have more effect on POI.

Final Analysis:   The primary purpose of a handgun is personal protection.   What shows on your target will work for you.   Just fine.

sfg



--- End quote ---

Thanks SFG.  Very interesting information.  Since you listed "bullet seating depth" twice, does that mean it has twice the effect as the other items you listed?  ;)

Fly

GreyGeek:

--- Quote from: OnTheFly on June 13, 2013, 11:09:19 PM ---CDO
--- End quote ---
CDO???

(IF it's good then I'm that too, because I LOVE math and physics.  Taught it through DiffEq at the college level for a decade. )

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