How to get most consistent velocity?


August 9, 2010, 01:20 AM
I am doing some research work with a .357 Mag chambered single-shot. The loads we are using fill the case about 50%. Would it be better to reduce our velocity range by going to a .38 Special or .38 Long Colt case to decrease the free volume? Would the bullet jump from the shorter cases be counter productive? Thanks for your insight.

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August 9, 2010, 07:04 AM
Powder choice can make a big difference. A good crimp can help. A heavier bullet can help. A .38 case vs the .357 cases can help a little. Powder choice is going to make the biggest difference by far. What velocity range and bullet weight are you shooting?

August 9, 2010, 11:14 AM
why not use a high volume powder such as H-110 or trailboss? you can get max velocity or plinking loads.

August 9, 2010, 11:50 AM
The current charge is roughly 7 to 8 grains of Unique with a 124/125 gr FMJ.

August 9, 2010, 01:18 PM
You worry too much.

I don't think Unique is particularly position sensitive as long as your load is generating sufficiently high pressure to burn. Your 7 to 8 grain load should be getting around 20,000 to 25,000 CUP, which should be plenty for good burn.

In loading them in a break-barrel single shot, they are probably getting the powder jarred to the front of the case every time when you drop them in the chamber the same way each time.

Your quest for accuracy might be better served with all the fine reloading details like proper case neck tension, consistent crimping.
And maybe even better bullets then 125 grain FMJ.


August 9, 2010, 10:47 PM
The goal of this exercise is to get a nominal 124 gr 9 mm FMJ to 456 m/s with a 7 m/s acceptable tolerance (+/- 1.5%). In English, that means 1496 fps +/- 23 fps or the shot is worthless. The .357 Mag chambered gun has a 34" barrel and a receiver/barrel size capable of handling .50 BMG, so overpressure is a meaningless term.

Here is the current recipe:

CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR assume any liability for any damage or injury resulting from use of this information.


Starline .38 Long Colt Brass (soon to be sorted by weight)

Federal Small Pistol Match Primer

7.2 gr Unique topped with 4.0 gr Cream-of-Wheat (to fill empty volume)

Winchester nominal 124 gr .355" 9 mm FMJ using only 125.0 gr specimens seated to 1/8" depth

Lee Roll Crimp

With this combination, I am doing a pretty good job of staying in my tolerance zone- much better than using the .357 Mag brass. However, there are still some issues:

Bullet Spin- The .38 LC brass seems to be designed for .358"/.357" lead cowboy bullets and does not like to grab the .355" FMJs, even with a taper crimp die. The bullets still spin and move back and forth a little bit after crimping with enough force to indent the jacket. Any ideas?

Should I use a card wad between the powder and Cream-of-Wheat to prevent any mixing?

Just FYI- The .38 LC brass shows no pressure signs after even such an extreme load. Good stuff!

Steve C
August 10, 2010, 01:01 PM
Winchester nominal 124 gr .355" 9 mm FMJ using only 125.0 gr specimens seated to 1/8" depth

The correct bullet diameter for the .357 mag and .38 spl is .357" for jacketed bullets and .358" for lead. I have tried using .355" 9mm bullets in .38 spl but never was able to get any accuracy out of them. Changing your bullet to the proper diameter will likely do more to improve accuracy than any thing else. The quality of the bullet is generally considered to be responsible for most of the accuracy in reloaded ammo.

August 10, 2010, 01:42 PM

You either need bigger bullets, or a smaller resizing die, or smaller expander.

If you are sizing the .38 Colt in a 9mm sizing die, it should already have the correct expander for .355" bullets. The expander should be at least .002" smaller then bullet diameter.

But regardless of that, I don't think you need to use cream-of-wheat, oatmeal, granola, kapok, dacron, card wads, or anything else.

If the bullet has proper case neck tension, which you don't have now, the powder will burn very consistently without filler.

If you don't have proper case neck tension, no amount of crimp will help at all.

Excess taper crimp can actually make the case neck tension worse, not better.

It will squish the lead core bullet, then the harder brass case springs back a little and the soft lead doesn't.


August 10, 2010, 01:54 PM
The goal of this exercise is to get a nominal 124 gr 9 mm FMJ to.....1496 fps +/- 23 fps

I think I would go back to .357 brass and try N110 or AA #9, which will be a compressed load, doing away with having to fool with the filler.

Actually, with that bullet and a 34" barrel, you should be able to achieve your velocity with N105, N350, or even N340.

9.1 Grs of N340 and a 125 Gr .357 diameter bullet (near max by Viht PDF) gave me an Average 1295 FPS from a 6" barrel with an ES of 28 and an SD of 11 last time I chronoed it. That was at 95% fill in a .357 case. It should fill up your .38 Long Colt brass and be even better ES & SD wise. 9.1 is under max, so you may get 100% fill in a .357 case. This load has always given me good ES & SD numbers, shoots like a laser, and should give you your velocity in a 34" tube. If it doesn't I would go with a slower Viht powder.

A WSP primer and 9.1 Grs of N340 in .357 Mag will give in the neighborhood of 1275 to 1350 FPS from a 6" tube, depending on the bullet, the crimp, and the gun. (Jacketed and plated)

This load appears safe in my gun using my load procedures. Check manuals and use at your own risk. Start low, and work up.

And do like rc posted to get good neck tension. All the info up front would have helped get better answers sooner.

August 10, 2010, 01:59 PM
+1 on the .357 brass in a .357 chambered test gun.

Using those way shorter .38 Colt cases leaves a lot of .380" chamber for the .355" - .357" bullets to rattle around in before it gets to the rifling.

That will allow gas blow-by, and inconsistent pressure & velocity.

And thats what you are trying to fight with the filler & stuff isn't it?.


August 10, 2010, 02:00 PM
A 124gr 9mm FMJ is the only bullet we can use in this research effort.

We had good luck with crimping the 9 mm in the .357 brass- there was just too much free volume and velocity variation.

The .38 LC brass is much thinner at the the case mouth than the .357 brass, and would not crimp well even with a 9 mm taper crimp die.

After this round of testing, I think we may try a different bulkier powder to better fill the .357 cases.

Thanks for your input!

August 10, 2010, 02:08 PM
Check the expander in the .357 die.
It is too big for .355" bullets.

Turn it down to .353" or so, or replace it with a 9mm expander plug.

Taper Crimping is not the answer to consistency my friend.


August 10, 2010, 02:29 PM
I expand the .38LC brass just enough so I can hard start the 9mm bullets using finger pressure, and finish out using the seating die for consistent depth. They seem to be snug prior to entering the roll crimp die. I tried varying the degree of crimp, but that did not work very well- still loose.

August 10, 2010, 02:37 PM
Hoo Kay.
One more time!

Check the expander in the .357 die.
It is too big for .355" bullets.
Turn it down to .353" or so, or replace it with a 9mm expander plug.


August 11, 2010, 10:44 PM
Well, I followed your folks advice and sized the cases using a 9mm sizing die. The crimp works much better now. :)

Here is load now (target velocity 426 +/- 7 m/s):

Federal Match Small Pistol Primer

.38 LC Starline brass (only cases with the same weight within .1 gr are used)

6.7 gr Unique

Index card over powder wad

5.0 gr Cream-of-Wheat

124.9 gr Winchester 9 mm .355 FMJ seated to slight compression.

We fired 5 shots and got 425, 422, 421, 422, 424 m/sec- Great precision and within the allowable tolerance for velocity, even with the .357 Mag chamber jump!

Thanks for your help!

August 12, 2010, 12:50 AM
Back in the 19th century, and well into the 20th, one common technique among target shooters was to first seat the bullet into the rifle’s rifling, then insert the cartridge case with the powder charge into the chamber. Much like the way a heavy artillery piece is loaded.

For certain, this would make moot the effects of neck tension and bullet jump.

August 12, 2010, 07:39 AM
got 425, 422, 421, 422, 424 m/sec- Conversion to FPS is calculator is in the shop.

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