Chronograph Loads and Extreme Spread

[03lover]

What would be considered a reasonable Extreme Spread for hand gun loads running 700 fps to 1000 fps?

As an avid shooter and reloader, I am familiar with many rifle loads and what to expect when chronographed.

More recently I have been running some of my light and mid-range 357 Magnum loads over the chronograph and the extreme spread, "ES" of many of these loads seem quite high. Some powder puff loads have an ES of 14 & 15 % and one at 18% of the average velocity. These loads run average velocities of 750 fps to 800 fps.

A load using a 145 gr. cast wad cutter over 4.0 gr. of 231 gives me an average velocity of 782 fps and ES of only 24 fps, only 3% of the AV. Another load, a 150 gr. cast round nose boolit over 4.0 gr. of 231 ran an average velocity of 747.5 fps and the ES was 44.8 fps for 6%.

I figure the higher the ES is, the less ballistic uniformity I have and that usually means less accuracy.

I have other 357 mag. loads to run over the chronograph that are known to be accurate and some that are what I call inconsistent. The inconsistent ones will sometimes shoot very tight groups and other groups are not much to talk about. This happens when five consecutive ten shot groups are fired.

It will be interesting to see what the chronograph will tell me about these loads.

I have several other hand gun calibers I intend to chronograph. They run from 38 Special to 9mm,38 Super, 45 ACP and 45 Colt. Would the acceptable ES be pretty much the same percentage for all calibers?

[wiljen]

I would think anything where the ES is <50 for hand gunning should be fine.

You have to remember that the ES is the absolute difference between highest and lowest which means each individual shot falls within half that of the mean for the group.

A maximum of 25fps faster or slower isn't going to change your group size by much and you can go stark raving mad searching for loads with a single digit SD only to find they don't shoot any better than the ones with a double digit SD.

[Rocky Raab]

At usual handgun ranges, ES has little if any detectable effect on accuracy. That sounds counter-intuitive, but it's true. You'd have to have some shots that merely fall out of the muzzle to affect accuracy inside 50 yards or so.

That said, a load with a low ES and a single-digit SD WOULD be more accurate at all ranges and is desirable on its own merits. A poor (high) ES and SD are indicative of some underlying incompatibility or inconsistency of loading technique, and should be investigated for that reason alone.

One can see high ES in loads using mixed brass, variable crimp, inconsistent primer seating, poor powder charge weight control, poor seating depth control - or simply poor choice of powder/bullet. Chronographs point to such things with glaring clarity. Check and eliminate such factors one by one and loads can improve magically. If not, it is simply a bad load combo that should be abandoned.

[mike in co]

i dont get to concerned on pistol data, just velocity. remember is a number based on a large sample say 1000 or more. we typically only do 5 or 10, so while its nice to have low numbers for consistancy, in a pistol and short range dont worry too much.

and it is not a percentage(%)...its a number. sd and es. one is just the spread and the other is...well its too early on a sunday morning to got into it.... lets just say its statistics and our sample size is too small.

mike in co



(rocky...no that is normallllllllll)

[Rocky Raab]

Even too early to type well, huh Mike? LOL!

[excavman]

A couple years ago I decided to chrono my favoite Sharps load. I load the 45-70 with 12 gr of Unique behind a 408 gr cast of ww + 5% bar solder hoping for 1100fps. The first round clocked in at 1102, second at exactly 1100, and the third came in at 1097. I quit right there, didn't want to ruin a good string. Needless to say that rifle shoots one hole groups at 50 yds.

Larry

[03lover]

Thanks guy's,

I do develope my hand gun loads with accuracy in mind first. When I find a load that gives me good accuracy, I always try the same load with at least three different primers. Quite often, a particular boolit and powder combination will prefer one primer over another and shoot even better. I also find some primer/powder/boolit combinations are more or less sensitive to powder position that often causes vertical stringing of groups.

It has been quite recent that I have started to chronograph many of the hand gun loads that I have developed along with loads still in developement. That is when I started to see some loads with ES figures that shocked me. Most of my rifle loads are much higher velocity than my hand gun loads yet the ES of the rifle loads are much lower.

Thanks again for the imput.

[mike in co]

i dont claim to know it all...there are lots of issues with hand gun ammo and numbers.

we shoot short distance and typically at large(body sized) targets....so we see little need for extremely small groups....go ask the bullseye guys.

but
case length, mixed cases, neck tension, crimp consistancy, primer seating, powder measure that throw plus or minus 0.1 suck when the case volume is so small.

in revolvers variation from hole to hole in the cylinder.

in semi's...no one seems to overcome the difference in the first round hand loaded by releasing the slide maunally vs the semi auto feed from a fired round.

yes most of my rifle data has smaller numbers than my pistol ammo.

but no issues with accuracy in my pistols either......most is less than 25yds, one match at 50 where rifles are always 100yds or more(exception for 3gun rifle).

mike in co