controlling velocity deviation

sask farmboy

sask farmboy

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I am working up an idpa Load for a 38 special. trying to decide on my amount of powder.

I started with polished 38 winchester brass
sorted each case by exact weight (I have 2000 empties to pick from)
sorted out bullets by exact weight to get enough to do a small batch.
weighed each powder charge on a freshly calibrated rcbs 505 scale
checked overall length of each cartridge.
weighed finished cartridges to double check all identical weights
chamber checked each

reloaded on a dillon 650, with cci primers and 5.4 grains Vihtavouri n350, frontier 158 grain plated round nose bullet

I used a 6 inch revolver to check my velocity over a chronograph at ten feet, I even used the same chamber in the revolvers cylinder to try and eliminate variance.

my fps was from 607.9 up to 722.5. that's a maximum deviation of 114.6 fps can I assume the powder is the source of the deviation? what other variables am I not taking into account?

I am using an semi light/average crimp.would a heavy crimp give me more consistency?
 
That seems like quite the extreme spread. Where on the charts is V n350 for burn rate? Are you sure your chrono didn't #### the bed? I scoop throw loads with less variance than that. I'd try them over another chronograph, and if the loads do the same, switch powder, or bump the charge if possible (depending where you are compared to a max load). Some powders are more consistent when they're burning at a higher pressure.
 
phatman said:
cylinder - barrel gap? who knows - looks like you got everything else sorted out...
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SoBored said:
phatman might have a point, try shooting three bullets out of the same chamber. If they are still all over the place, you probably have a crimp issue IMO.
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I shot all of them from the same cylinder

I used a 6 inch revolver to check my velocity over a chronograph at ten feet, I even used the same chamber in the revolvers cylinder to try and eliminate variance.
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saskgunowner101 said:
. I'd try them over another chronograph, and if the loads do the same, switch powder, or bump the charge if possible (depending where you are compared to a max load). Some powders are more consistent when they're burning at a higher pressure.
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I am on the low side of the scale, but I also don't want to have to shoot +p to get consistency. i think I will experiment with my crimp and if that does not work then I will try a different powder because once I start using mixed unsorted brass and bullets of slightly varying weights then I would likely be all over the place again.

Hoping its not my crony. but I guess it would be prudent to check against a second chrony's results.

thank you guys for the suggestions.
 
I just checked the V site, and the powder burn rate chart at Hodgdons, and I'm thinking you need a quicker powder if you don't want to turn up the juice. Titegroup or Clays would bump up the pressure for a consistent burn, not much recoil, and not a high fps.
 
The other factor in such velocity variation could be the strength of the hammer fall on the primer. If the revolver was 'worked on' and the hammer spring lightened up, it is possible that it is not hitting the primers well, causing the variation.
I applaud your efforts, but far too much effort to develop a short range load. If you were shooting a 1000 yard target rifle, perhaps. It is your time, and you can spend it as you wish, but I would not.
If you are trying to match factory ballistics (approximately 158 grain bullet at around 800 fps) then you have a whole bunch of choices, such as bullseye, red dot, 700-x, 231, titegroup, all of which meter well enough and ignite very well.
 
saskgunowner101 said:
I just checked the V site, and the powder burn rate chart at Hodgdons, and I'm thinking you need a quicker powder if you don't want to turn up the juice. Titegroup or Clays would bump up the pressure for a consistent burn, not much recoil, and not a high fps.
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This is probably the issue - trying to use a powder at the low end of its pressure range often leads to inconsistency. Do other loads in that gun display less variation?

If you want a load that has an MV in the 700 fps range (which is very low, even for a mild 38 Special load), you need to be using a much faster powder such as Clays, or my favourite HP-38 (Win 231).

Of course if the load is accurate, then there's no problem, regardless of what the chrony tells you.
 
The other factor in such velocity variation could be the strength of the hammer fall on the primer. If the revolver was 'worked on' and the hammer spring lightened up, it is possible that it is not hitting the primers well, causing the variation.
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I tried them some in my 4.2 686 and it also had a big variance

I picked up some clays, some 231, and some wst. so I will experiment with those.

thank everyone for the help
 
Your care in prepping your ammo is superb (and far, far more than what is needed for this - though none of what you did would hurt.)

Variation in neck tension can have an affect, but Andy has offered the most likely explanation.

Choosing the fastest powder available to you (e.g. Bullseye) will probably give you the most consistent m.v.'s at the moderate velocities you seek.
 
Trying different primer brands can make a difference as well.
A heavier crimp will also boost your igniton pressures and create a more consistant powder burn.

Your case/load prep is definitely overkill for short range work.
But if you enjoy it, do it.

I do all of these steps and more for my shooting out to 2000 yards. This is where you NEED to control every variable imagineable! Its tough to do well, but extreamly satisfying when you produce MOA groups!

Straight shootin, and keep it fun!
 
Andy said:
Of course if the load is accurate, then there's no problem, regardless of what the chrony tells you.
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This is what I am after in working up a load - I really don't care how fast it goes - as long as it goes where I point the gun.

Now if I were shooting a lvl 3 - then I'd make sure it met min pf...
 
If there is a lot of room in the cases, perhaps the position of the powder in the case could be a cause. Did you try tipping the muzzle up before each shot so the powder is against the primer every time? Just a thought.
 
I only did that level of prep work so I could eliminate many of the variables so I could establish what type of powder I will be using for my regular loads(I will be making thousands of rounds), I will not be doing that kind of prep work for all the ammo, just my test loads. once I settle on a powder its back to unsorted misc brass with the powder measured by the powder dump in my Dillon.

I think it is worth the effort.
 
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