Seating force variance

[JFASH]

I'm using a km arbor press (with a force pack) and my problem is brass segregation. I would like to know when you group by seating force, how many pounds do you deviate from in a group? 1 pound, 2 pounds?
Thanks
Joe

 

[JFASH]

I don’t use a force pack however I do have a thought.
Color the ones that vary 2 pounds than note any difference on paper,
Report Back”
Please

Ill try that spj

I don’t use a force pack however I do have a thought.
Color the ones that vary 2 pounds than note any difference on paper,
Report Back”
Please

My cases are annealed lapua brass and I'm getting (at the most) a spread of about +/- 6 pounds. Im going to test this out saturday. I'll report back. Thanks spj.
Joe

 

[JFASH]

Do you use a bronze brush on the inside of the necks or nylon.

I started making a pass or two with the Bronze followed by a clean up pass with the nylon, I’ve since noticed a difference in seating force.
(More consistent)

I've been using a nylon brush but the next time i reload the cases, I'll try a bronze brush. Ive tried this with annealed and unannealed cases. Are you annealing?
Thanks

 

[JFASH]

Yes, i think im going to go the unannealed route next time.
Thanks

 

[JFASH]

Another question spj... do you clean your cases? If you do, are you wet tumbling or dry?
Thanks

 

[jds holler]

It is my sincere hope that a few pounds variance in neck tension will be of small consequence, considering the 50,000 + psi working pressure of a typical rifle cartridge. jd

 

[JFASH]

Thanks spj

 

[JFASH]

I'll report back

 

[mikecr]

It is my sincere hope that a few pounds variance in neck tension will be of small consequence, considering the 50,000 + psi working pressure of a typical rifle cartridge.

Not a variance of neck tension, but of seating force.
Even if you normalized seating friction, and removed neck up-sizing(yielding) with seating, the remaining correlation with pushing force of a bullet to spring back gripping force, is not 1:1. There is leverage in play here.
We currently have no way to actually measure neck hoop tension, which is what grips a bullet, and is overcome on firing pressure to release it.

There is also the leverage in powder's burn timing character. With this, relatively slight confinement adjustments significantly affect pressure peaks.

 

[JFASH]

Not a variance of neck tension, but of seating force.
Even if you normalized seating friction, and removed neck up-sizing(yielding) with seating, the remaining correlation with pushing force of a bullet to spring back gripping force, is not 1:1. There is leverage in play here.
We currently have no way to actually measure neck hoop tension, which is what grips a bullet, and is overcome on firing pressure to release it.

There is also the leverage in powder's burn timing character. With this, relatively slight confinement adjustments significantly affect pressure peaks.

Do you group by seating force? If so, what would be the max/min poundage that you deviate from?
Joe

 

[mikeinct]

We did this before. Take say 25 loaded cartridges. All that have been nylon brushed after the mandrel expanding. You said you are seeing about 7 lbs of force variance. Divide them up in 4 lots, in 2 lb increments. one lot will be random one from each group. Set a target out with 4 bullseyes. minus -2lbs from the avg. then the random lot, standard, then the plus 2 lbs group. Take your time & don't mix up your shots. one or two into each bullseye until you have shot all 4 bullseyes. A couple of shots per at each target each rotation. Start at the first lot & bullseye again. 2 more shots per bullseye. in a round robin fashion. go slow it takes time to shoot thru this. However you run this 3 5 6 shots per target. then report back...Mike in Ct. PS watch the wind flags

 

[JFASH]

We did this before. Take say 25 loaded cartridges. All that have been nylon brushed after the mandrel expanding. You said you are seeing about 7 lbs of force variance. Divide them up in 4 lots, in 2 lb increments. one lot will be random one from each group. Set a target out with 4 bullseyes. minus -2lbs from the avg. then the random lot, standard, then the plus 2 lbs group. Take your time & don't mix up your shots. one or two into each bullseye until you have shot all 4 bullseyes. A couple of shots per at each target each rotation. Start at the first lot & bullseye again. 2 more shots per bullseye. in a round robin fashion. go slow it takes time to shoot thru this. However you run this 3 5 6 shots per target. then report back...Mike in Ct. PS watch the wind flags

I'll try that also.
Thanks
Joe

 

[mikeinct]

I should spend more time at the bench. You know instead of this friggin desk...Mike

 

[mikecr]

Do you group by seating force? If so, what would be the max/min poundage that you deviate from?

I don't use a K&M or bullets for force measure.

This is a comparison, only indicative of neck tension(with all else normalized), and not a direct measure.
I happen to use a Sinclair mandrel die in which I've installed a load cell. My measure is of pre-seating forces, which I can adjust to matching -prior to seating actual bullets.
These numbers are dimensionless, not in pounds, and pounds in particular have no meaning here. All you need is to be 'on scale' (any scale) for the range of seating forces presented and compared.

What your numbers mean is a local matter, in no way correlating with anybody else (including those also using a K&M). Your necks are not the same hardness, your sizing not to the same interference fit, your seating frictions are different.
So when you wonder 'what do my numbers mean?',, they're your numbers, it's for you to explore.
It's been suggested that you group & shoot em. That's a logical next step.

 

[JFASH]

I also use a sinclair expander prior to seating. When i said pounds, i should've said "dial setting" on the indicator. The force varies slightly. I wonder if neck turning would make the numbers more uniform?
Thanks
Joe

 

[ratbuster]

Once when loading a few hundred 20 practical varmint rounds I decided to do a test to determine what effect seating force had on velocity. Of that lot I selected 5 each cartridges of heaviest and lightest seating force. Those 10 cartridges were the most extreme outliers, that is the 5 lightest were much much lighter than the 5 heaviest. The shocker was the velocities from the two groups were super close together and I saw no difference in group size either. Totally unexpected. Now I pay no attention to seating force.

 

[jds holler]

Once when loading a few hundred 20 practical varmint rounds I decided to do a test to determine what effect seating force had on velocity. Of that lot I selected 5 each cartridges of heaviest and lightest seating force. Those 10 cartridges were the most extreme outliers, that is the 5 lightest were much much lighter than the 5 heaviest. The shocker was the velocities from the two groups were super close together and I saw no difference in group size either. Totally unexpected. Now I pay no attention to seating force.

That^^^ is exactly the kind of info I'm interested in, and need to do for myself. I wonder if jam or distance from jam would make a difference in your results. jd

 

[ratbuster]

That^^^ is exactly the kind of info I'm interested in, and need to do for myself. I wonder if jam or distance from jam would make a difference in your results. jd

JDS

That's something I've not considered. Given there are so many variables when it comes to shooting for precision I imagine there are scenarios where results could be quite different than what I saw with my test.

 

[group therapy]

@Puzzaz01 should chime in and of course the mighty "guffey"

 

[jds holler]

F. Gufffffeeeeeeyyyyy wheeeeerrrrrreeee aaaarrrrrrreeeeee yoooouuuu.