How much should the velocity vary in 9mm during a chrono test?

[tazman]

I haven't had access to a chronograph before and don't really know what to expect. I know there will be some variation but I am not certain how much.
I will grant that I am not doing a lot to reduce the variables. For instance I am using mixed brass and using a powder measure to throw charges. Neither am I weighing the boolits so they match perfectly in weight. The accuracy is quite good though.
I got extreme spreads of 40fps with the heavier boolits using slow powder and as high as 80fps differences with the lightest that I shot using the fastest powder.

My question is how much variation in velocity will there be with this type of situation in a 9mm pistol for a 10 shot string?
Is this usual or is it too much variation?

[williamwaco]

Those are good variations.

I am not saying they can't be improved but they are good readings and that is not enough variation to affect accuracy.

[FergusonTO35]

I consider a max spread of 5% to be ideal. I have also found that most factory ammo produces larger spreads than reloads. My current defensive load has a spread of 4%.

[Scharfschuetze]

I just worked up some loads for my 9mm pistols in June using a new style of truncated cone boolit of 124 grains cast fairly hard. These loads, other than the Unique load, are all works in progress and are fairly light. All will eventually be worked up to hopefully 1150 fps if accuracy and safety allow.

Here's a summary. These are all based on 10 shot strings:

Tight Group: Es 28 at a velocity of 1015 fps
Green Dot: Es 57 at a velocity of 1033 fps
Winchester 231: Es 47 at a velocity of 1000 fps
Herco: Es 82 at a velocity of 1000 fps
Unique: Es 68 at a velocity of 1160 fps

Unique, as usual, works very well in the 9mm; but it has never given me the best ballistic uniformity. Tight Group is living up to its reputation of good ballistic uniformity and clean burning. Other than the Tight Group, these are all pretty much "old school" powders and really provide good predictable performance.

The mature Unique load from my High Power at 25 yards.

[tazman]

Thanks guys. I really had no Idea what possible problems I might have been looking at and simply not understanding.
I won't be concerned about it now.

[rintinglen]

My rule of thumb for pistols and revolvers is anything under 50 fps ES for 10 shots is a keeper, but I have shot some pretty good groups with stuff that was closer to a 70 fps spread. I worry more about accuracy than velocity.