Hi All,

I have been reloading 38s for a couple of years and today I had the opportunity to chronograph one of my loads, 158 gr, SWC with 3.8 gr. Win 231 fired out of a 4" barreled S&W model 10.

The data from 6 shots was

<TABLE style="WIDTH: 96pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=128 border=0 x:str><COLGROUP><COL style="WIDTH: 48pt" span=2 width=64><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; WIDTH: 48pt; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right width=64 height=17 x:num>742.5</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; WIDTH: 48pt; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent" width=64>ft.sec</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right height=17 x:num>777.6</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent">ft.sec</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right height=17 x:num>809.7</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent">ft.sec</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right height=17 x:num>806</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent">.0 ft.sec</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right height=17 x:num>776.5</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent">ft.sec</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right height=17 x:num>765.7</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent">ft.sec</TD></TR></TBODY></TABLE>
<TABLE style="WIDTH: 204pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=271 border=0 x:str><COLGROUP><COL style="WIDTH: 104pt; mso-width-source: userset; mso-width-alt: 5046" width=138><COL style="WIDTH: 100pt; mso-width-source: userset; mso-width-alt: 4864" width=133><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; WIDTH: 104pt; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" width=138 height=17>Mean</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; WIDTH: 100pt; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent" align=right width=133 x:num="779.66666666666663">779.6666667</TD></TR></TBODY></TABLE>
<TABLE style="WIDTH: 204pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=271 border=0 x:str><COLGROUP><COL style="WIDTH: 104pt; mso-width-source: userset; mso-width-alt: 5046" width=138><COL style="WIDTH: 100pt; mso-width-source: userset; mso-width-alt: 4864" width=133><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; WIDTH: 104pt; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" width=138 height=17>Standard Deviation</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; WIDTH: 100pt; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent" align=right width=133 x:num="25.243507416101295">25.24350742</TD></TR></TBODY></TABLE>

According to my manual, the Mean is pretty close to the published value(783ft/sec) but I was a little suprised at the range of values. I have a single stage press and recheck the powder weight every 5-10 rounds, so I'm pretty certain the powder weight is within 0.1 gr.

Is it typical to see this range in velocity or is there something I'm not doing correctly. Bad crimp?

TIA

Tim
Rocklin CA

I looked back at the exact load I chronographed a year ago and it is almost exactly the same. My SD was 24.8 and average vel was 785. I used HP38 powder though which is an exact substitute for W231.

Yes, you can get a velocity range like this. However, you can also look at the data and see that you have an extreme spread of just under 60 fps. Or, in other words, your shots are all plus or minus 30 fps of your average (this is somewhat what the standard deviation is telling you, but the sample is too small to make it meaningful).
Trying to weigh the powder won't make a difference. This could be due to the pressure for the powder being slightly sub-optimal, or variations in the impact of the hammer on the primer, or differences in crimp and neck tension due to different lots of brass, or all of the above.
Personally, I use a powder measure to throw all of my pistol loads, and they work fine.
Lastly, you might be getting some chronograph errors depending on the type you are using. If it is a box on the table beside you the muzzle blast can sometimes cause problems (although you usually get much stranger readings - trust me, a .44 doesn't help the chronograph box work well).
Are they accurate? If so, don't worry too much.

Thank you all!

Being an engineer (SW engineer at Hewlett Packard) I'm like to understand data and why things happen.

Happy reloading & shooting!

Tim

That's actually a very good result. Look at it another way and your velocities are within 4% of the mean. That's quite good considering all the other variables involved. Even if you took the "NASA approach" and individually selected each and every component through rigorous analysis of every one (and spending a couple hundred bucks per round!), you wouldn't be able to tell any difference whatsoever from shot to shot.

Think back; were you ever aware of even the slightest difference shot-to-shot before you put them over a chronograph? No. Groups make you happy? Yes. Well, nothing has changed.

Tim,

As Rocky said, that's pretty reasonable. If you want to play with making it still more consistent, there are steps you can take, but whether they have practical value is questionable? Your sample, as Al said, has no real statistical significance. Statisticians usually figure it takes about 30 samples to get a bell curve distribution that is reasonably symmetrical, and that is a string that is certainly practical to undertake with the .38.

If you want to improve consistency just to satisfy your curiosity, you can trim your cases to equal resized length to make the crimp more consistent. They should all be the same brand and lot and have had the same number and kinds of reloadings made with them so the brass work hardening level is the same. You could try Federal 100M small pistol match primers to see if that makes a difference? You could have your cylinder chambers reamed to matching maximum dimensions (a standard revolver accurizing step). There's an outfit called cylindersmith.com (http://cylindersmith.com/) that does it for under $40. You could try a faster powder to get more complete burning in the barrel. Since the case has a lot of unused space in it, you may find the simple act of pointing the gun skyward to get the powder over the primer before leveling it to fire will improve ignition consistency and tighten your stats?

Main thing is to have fun.

Think back; were you ever aware of even the slightest difference shot-to-shot before you put them over a chronograph? No. Groups make you happy? Yes. Well, nothing has changed.

:D:D, I have learned to never chronograph a load, until I've found the best accuracy mix. When I'm feelin' good about that, I check the speed. Most loads come in a bit short of your "wish", and variation from day to day can be surprising. But when they're all in the middle, who's to complain. I'm pretty sure I never got within 25fps of a listed load velocity, and 100fps +/-, is more like reality.