Erratic Muzzle Velocities on 9mm

Hoag

Hoag

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I was doing a new load work-up for my 9mm yesterday. I had shot a couple loads for accuracy and then shot them through the chronograph to check their muzzle velocity and to see if they would make IDPA Power Factor. One was fairly constant, but the other was very erratic. Both loads were smaller sample sizes (strings size) than I would normally do, and I know that a larger string size would tend to bring in the extremes and give a better overall view of the load, but I didn't have any more with me.

Here is the baseline of what I loaded.
2 loads. Both loaded on a Dillon 550B using a Lee Autodisk Powder Measure (it dispenses powder based on volume not weight).
Both loads were:
Range pick up brass
Campro 124 grain JHP bullets
CCI small pistol primers
COAL: 1.110"
The consistent load was 0.32cc (approx 3.7 grains) TiteGroup
The erratic load was 0.30cc (approx. 3.5 grains) TiteGroup.

Both groups were shot through a CED M2 chronograph.

.30cc String
1268
1276
1149
973*
1184
1141
1052*
1090
1146

Ave 1042
SD 91.4
ES 303
*These shots were recorded by the Chronograph as an "Outside the Velocity Range" errors.

.32cc String
1016
1044
1022
1036
1053
1031
1038
1032

Ave 1034
SD 10.9
ES 37

Does anybody have any thoughts as to what would cause the 30cc loads to range from 972fps to 1276fps with no identifiable trends? The only thing that I can think of is that this load may be approaching the point where there is so little powder in the round that it is burning at a different rate from round to round as the powder shifts inside the casing.
 
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Caused by inconsistant powder measure throws. Not an uncommon problem, I had the same problem until 10 years ago. Replaced the Lee equipment with Dillon.
 
I recently had a similar problem using a Lee powder measure. I had previously changed
it to the adjustable bar to try different powder loads using Titegroup.
3.4 Grains of Titegroup resulted in erratic loads. I don't have a chrony but
I could feel the difference.
Then I retried the same load but filled the powder hopper to the top assuming that more powder
in the hopper would make the charge more consistent. Problem solved.
I think that the Lee powder measure has a small hopper that needs to be kept full or close to full
to be consistent on small charges.
 
Too light a load (below Starting) and probably inconsistent. Going below suggested starting load which puts the powder below its intended operating pressure is the most common cause or inconsistent MV's. If Start Loads are "safe", below Start is not "safer", it's typically the opposite.
 
RePete said:
Caused by inconsistant powder measure throws. Not an uncommon problem, I had the same problem until 10 years ago. Replaced the Lee equipment with Dillon.
Click to expand...


Good equipment always help.
Make sure that the powder hopper is full of fluffed up powder. Keep it at the same level when loading.
I never keep the first 3 throws
 
Last week I got a squib in my NP34. The load was 3.6 titegroup with Berry RN 124 gr. The COAL was at around 1.125
The cartridge fired but the bullet got stuck in the barrel. 3.6gr appears to be dangerously under powered.
 
Kryogen said:
Good equipment always help.
Make sure that the powder hopper is full of fluffed up powder. Keep it at the same level when loading.
I never keep the first 3 throws
Click to expand...

Yup. I typically throw 10 charges back into the hopper. Then I throw 10 more and weigh them and get an average for the 10 charges. As I have found though, that obviously will not pick up inconsistencies from throw to throw.
 
plastic powder measures deal poorly with static electricity.
Rub everywhere with a bounce sheet prior to loading if air is too dry.
 
edojan said:
Last week I got a squib in my NP34. The load was 3.6 titegroup with Berry RN 124 gr. The COAL was at around 1.125
The cartridge fired but the bullet got stuck in the barrel. 3.6gr appears to be dangerously under powered.
Click to expand...

I think you may have a problem with your throw, or a missed charge.
 
Innercity said:
I think you may have a problem with your throw, or a missed charge.
Click to expand...
its possible. Hodgdon formal data lists 3.6gr as the starting load - this is why I used it in the first place. It is likely that something went wrong in my case (pun intended)
 
I've had good luck with those discs and titegroup.
Seems you get a good velocity for that charge but it is common to get erratic results with the smaller auto disc sizes...
 
Since the Disks stop at 3.3/3.4ish, I d say you used the adjustable bar which has been known to be flawed at minimum capacity (the slit doesn't face the hopper's hole properly).

I've been shooting 3.4 (.30 CC cav) for years in 9mm with a 125LRN, and it's a fine load; but I've also been planning on sleeving an other cavity with a section of plastic tubing for use with an older gun (a piece of adhesive label might work too).

If you really want to keep using the bar, you can shim/epoxy the cavity to move its opening (this will lower the max capacity).

modified_adjustable_charge_bar_brightwood_be.jpg
 
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kg said:
Since the Disks stop at 3.3/3.4ish, I ll say you used the adjustable bar which has been know to be flawed at minimum capacity (the slit doesn't face the hopper's hole properly).

I've been shooting 3.4 (.30 CC cav) for years in 9mm with a 125LRN, and it's a fine load, but I've also been planning on sleeving an other cavity with a section of plastic tubing for use with an older gun (a piece of adhesive label might work too).

If you really want to keep using the bar, you can shim/epoxy the cavity to move its opening (it will lower the max capacity).

modified_adjustable_charge_bar_brightwood_be.jpg
Click to expand...

I am using the disks, not the adjustable bar, but thanks for the tip if I do switch to the bar.
 
The Lee Autodisk system is quite good but does have problems with low charge weights of bulky powders. When I could find Alliant Promo I used it a lot because it was so reasonably priced and behaved almost identically to Red Dot. However, the charge weights were all over the place so I had to visually check each charge (I use a Loadmaster) to catch light charges. However when I use finer grain powders like Bullseye or 231 even the light charges are dead on. I think the bulky powders create a bridging problem with the smaller disks. Once I jumped my Promo loads up to 3.7 and higher the problem cleared up. I also tried the adjustable charge bar and it was even worse than the disks
 
Hoag said:
I am using the disks, not the adjustable bar, but thanks for the tip if I do switch to the bar.
Click to expand...

Uh-Oh! I've got to confess that I didn't read your whole post before answering. I would suggest a repeat of the 30cc test. The highest velocity might mean that you actually used the .34cc cavity (sorry, just trying to understand).

The irregularity might have happened because the powder had just been poured in the hopper (first cartridges loaded?), or because you used mixed brass.
 
bulky powders such as unique meter with more variation in the lee auto disk.
The adjustable charge bar deals poorly with small loads.
Also, one thing to note, depending on which side you reinstall the hopper, the hole in the charge bar might or might not be completely aligned with the hole in the hopper. It will work, but you will get variation. Double check this.

With the auto disk, no static, smaller powder flakes, and the hopper the right way, it works pretty well. I have it on my load development loadmaster.
 
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