Is it just my impression but do typical magnum handgun loads have a high standard deviation in velocity readings?

For instance, typical full power loads in my high power rifles will deliver standard deviations of 0.5%-1.5% of average velocity (10 round sample population). FWIW, two .458Lotts and a .450Ackley consistenty deliver the lowest SD readings of all my weapons. Some Lott loads show an extreme spread of only 15fps!

The .357s, .44s, .454 and .475 all usually deliver 1.5%-5% SDs, especially with powders like H110, W296, and 2400. It typically doesn't affect the accuracy of the load but makes me wonder if I'm consistently missing something. Perhaps flecks of lubricant are tripping my chrono sensors?

Problem is that SD`s can have absolutely nothing to do with accuracy.It is a meaningless number and I do not worry about it.

High deveation seems to be a funtion of slow powders, and short barrels. I've shot the same ammo in revolvers, and then carbines, and the variation goes way down in the longer tube.

Lies, damn lies and statistics....

How accurate is the load?

My most accurate loads run around 3-5moa, plenty run around 4-6, and my plinkin' ammo usually runs about 8-10moa. None of these involve lapping the guns, perfecting bullet fit, tuning crimp etc. - they're all just load and go.

I don't worry about SD if the load groups well, more just a point of curiosity.

Interesting about the slow powder and barrel length, Kaboom, thanks for the info!

Yeah, the numbers mean little for accuracy that most expect from a revolver yet there is something to it.
Too strong a primer in the smaller cases like the .45 ACP, .44 and even the .45 will move bullets different amounts before good ignition so your case capacity is always changing.
Using a Fed 150 in the .44 can cut groups by 2/3's. They also reduce groups in the .45 Colt.
SP primers in the ACP from a revolver will cut groups.
Next is case tension, it must be good and even from case to case. The worst problem is too soft a cast boolit that gets sized when seated or the brass is opened too much with a Lyman "M" die, etc. Soft boolits also slump into all kinds of shapes different then what you cast. Believe it or not, fast powders are harder on boolits because pressure rise is too fast. What is called a low pressure load has slammed the boolit all at once before it moves much.
Then crimp! Bullets can move out in other chambers from recoil with low case tension so the first thing done it to make the crimp harder. That will break the tension more and start to bulge brass below the crimp.
Soft boolits can also be sized by the crimp that will not fully open so you get gas cutting and leading just like shooting a boolit too small.
The revolver is easy to load for but there are things you just can't do, things that will be OK in a rifle. The revolver bullet is free to move before any resistance is met.
Barrel length has little to do with high numbers or accuracy although recoil is higher and can move bullets easier. Slow powders just burn more in front of the gun instead of in the gun. What happens while the bullet is still in the gun must be consistent.

Six chambers ? Six different accuracy results !Set up six targets ,fire 5 rounds per chamber ,one chamber per target. Interesting results !
Lots of other variables too ! And the poor SD and BC of handgun bullets make them slow down quickly ! But the 200m steel ram can still be knocked down !

A load with good internal ballistics can be inaccurate but a load with poor internal ballistics will not be accurate. However, at typical handgun ranges it is many times difficult to tell the difference if just shooting off hand.

With a 10 shot test string (excellent BTW) I look at both the SD, the ES and on target accuracy with groups fired at 50 yards with hunting revolvers. Accuracy is dependant on the quality of the firearm and how well the bullet fits the throats and is suitable for the twist and velocity used at. I've found over the years with magnum loads in magnum revovlers the really accurate loads will have an ES less than 100 fps (preferably less than 70 fps) and the SD should be 25 - 40% of the ES. For example; the last 10 shot test of my .44 magnum FTBH with the classic keith load of 22 gr 2400 under the RCBS 44-250-K bullet gave an ES of 39 fps with an SD of 13 fps. Those 10 shots went right into 3" at 50 yards from a sandbaged rest which is about the best my tired old eyes will do. H100 under the 240 XTP runs an ES of 60 -70 fps with SDs in the mid 20 fps range.

If you have ESs over 100 fps then you're using the wrong powder with whatever bullet.

Larry Gibson

Lot's of good answers above. Basically the proof is in the target, and by that I mean a 10 shot group and non of this "called flyer" nonsense. If you want to egt serious then you can certainly plot the bullet impacts on a plotter at your hand so that you can try to correlate high velocity variations with POI. Good luck!
For high power rifle at long ranges, 600 yards plus, SD can be a good predictor of performance but I don't think that is true for the less precise handgun shooting. BR shooters also use statistical measurements just to eliminate another variable.
Peter.

quote:

Originally posted by mete:
Six chambers ? Six different accuracy results !Set up six targets ,fire 5 rounds per chamber ,one chamber per target. Interesting results !
Lots of other variables too ! And the poor SD and BC of handgun bullets make them slow down quickly ! But the 200m steel ram can still be knocked down !

The six target test is incredibly enlightening! I have done it with my GP100 and as you say, there is a great variation from chamber to chamber with accuracy and to some degree of point of impact.

Havn't tested that with my Oehler yet but when i get it up and running, I will do the test. Not that it matters at 25 - 50 yds much, but it will be fun to experiment.

quote:

A load with good internal ballistics can be inaccurate but a load with poor internal ballistics will not be accurate. However, at typical handgun ranges it is many times difficult to tell the difference if just shooting off hand.

With a 10 shot test string (excellent BTW) I look at both the SD, the ES and on target accuracy with groups fired at 50 yards with hunting revolvers. Accuracy is dependant on the quality of the firearm and how well the bullet fits the throats and is suitable for the twist and velocity used at. I've found over the years with magnum loads in magnum revovlers the really accurate loads will have an ES less than 100 fps (preferably less than 70 fps) and the SD should be 25 - 40% of the ES. For example; the last 10 shot test of my .44 magnum FTBH with the classic keith load of 22 gr 2400 under the RCBS 44-250-K bullet gave an ES of 39 fps with an SD of 13 fps. Those 10 shots went right into 3" at 50 yards from a sandbaged rest which is about the best my tired old eyes will do. H100 under the 240 XTP runs an ES of 60 -70 fps with SDs in the mid 20 fps range.

If you have ESs over 100 fps then you're using the wrong powder with whatever bullet.

Larry Gibson

My loads with the .44 with a 320 gr LBT will have a SD of 11.5, MAD of 9.9, ES of 29 fps and under 1" at 50 yards.
Control of case tension and crimp.
Yes, the numbers are important because they define how you load.
Now think some more! I have worked loads that have much smaller numbers yet would not group.
That is why a chrono is never used to look for accuracy. Leave the thing home, then see what your velocity is AFTER you find accuracy. Ignore the other numbers because if you try to improve them your accuracy might just go away.