SD and Accuracy

Guy B. Meredith · June 16, 2001, 08:06 PM

What does your experience tell you about the relationship between Standard Deviation, Extreme (velocity) Spread and accuracy? I know about theory, but what has real life experience shown?

I am looking at developing a low velocity (about 900 fps) load for .357 magnum cases and started with the loadings recommended for AA#2. I wanted to get my feet wet and I normally use AA#2 for .38 spl. SD averaged about 25, Extreme Spread up to about 105 fps. Offhand shooting created 2" hole at 15 yards, but I am not the ultimate in accuracy myself.

I am now checking out AA#7 and may go back to AA#5 for lower cost and versatility in .38 spl and .357 magnum.

After working in the 4.8 gr range so long, dumping in 10 gr of anything makes me tense. Oh well, I trusted the charts for the 4.8 gr AA#2 for .38 spl, I trusted the charts for the 5.8 gr AA#2 for .357 magnum, I suppose I should trust the charts for the 10.5 gr AA#7 in .357 magnums.

Just seems like such a lot of powder...

WESHOOT2 · June 17, 2001, 09:46 AM

"Should I use chronograph data to tell me if my load is 'accurate'?"

..or should I use my gun?....

FACT = SD, ES, AD, etc., WILL NOT tell you if a specific load is accurate from a specific gun.

I demand low deviations from my defense ammo so I can expect correct terminal performance, but when seeking ACCURACY ONLY I have learned to trust the gun. Chrono data means zilch if the bullets enter the same hole.

June 16, 2001, 08:06 PM	#1
Guy B. Meredith Senior Member Join Date: August 29, 1999 Location: Salem, Oregon Posts: 1,581	SD and Accuracy What does your experience tell you about the relationship between Standard Deviation, Extreme (velocity) Spread and accuracy? I know about theory, but what has real life experience shown? I am looking at developing a low velocity (about 900 fps) load for .357 magnum cases and started with the loadings recommended for AA#2. I wanted to get my feet wet and I normally use AA#2 for .38 spl. SD averaged about 25, Extreme Spread up to about 105 fps. Offhand shooting created 2" hole at 15 yards, but I am not the ultimate in accuracy myself. I am now checking out AA#7 and may go back to AA#5 for lower cost and versatility in .38 spl and .357 magnum. After working in the 4.8 gr range so long, dumping in 10 gr of anything makes me tense. Oh well, I trusted the charts for the 4.8 gr AA#2 for .38 spl, I trusted the charts for the 5.8 gr AA#2 for .357 magnum, I suppose I should trust the charts for the 10.5 gr AA#7 in .357 magnums. Just seems like such a lot of powder...

June 17, 2001, 09:46 AM	#2
WESHOOT2 Senior Member Join Date: February 20, 1999 Location: home on the range; Vermont (Caspian country) Posts: 14,324	WELCOME TO MY WORLD "Should I use chronograph data to tell me if my load is 'accurate'?" ..or should I use my gun?.... FACT = SD, ES, AD, etc., WILL NOT tell you if a specific load is accurate from a specific gun. I demand low deviations from my defense ammo so I can expect correct terminal performance, but when seeking ACCURACY ONLY I have learned to trust the gun. Chrono data means zilch if the bullets enter the same hole. __________________ . "all my ammo is mostly retired factory ammo"