Powder charge and seating depth

[cajun]

Actually you can find a forgiving load away from the lands.

More Bullet Jump Research!

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[Mikecr]

One more anecdote - when testing a barrel tuner, you WANT bad groups so you can really see how the tuner moves them. So you have to find a bad load to test the one particular thing you're changing. If you shoot one hole at 100, there's no real way other than going really far away to see the changes. If you shoot 3" at 100 yards you can see the tuner swing the group around. You want to see the effects of seating depth, so pick a charge weight that makes bad groups so you can see the group size move with seating depth. When you bring the depth and charge node together, you should have a resilient, long lasting load going forward that doesn't need to be tweaked for a while.

This is what I'm trying to relay to folks.
There is a saying I adopted while in the military: Broken is half way to fixed.
As in, it can be easier to define a problem when it's broke, than when it's not.

 

[WildRose]

Actually you can find a forgiving load away from the lands.

More Bullet Jump Research!

This is the 4th article in a series on some new research on bullet jumps. Here is a recap of the pr...

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This is true for some bullets as was mentioned. The ELD-M however does not have the Tangent Ogive of the Berger bullets. Bullets with the Secant Ogive are much more sensitive to seating depth than those with a secant Ogive.

That's why Berger developed the Hybrid Ogive line of hunting bullets so they'd be less sensitive to seating depth.

 

[6pakzak]

I agree with you, concentricity does make better groups. What I'm getting at is along the lines of one of Mike's points, if you want to test something get out of the node. So while a honed die is the best option long run, in the short run experimenting with the bushings and mandrels in a not-good place for concentricity is fine because you know you can tune out the effects induced by it because you've done it.

Let me try another way - accept worse groups while you're messing with the neck setting and deciding which spec to get a honed die for. The groups will get better when you start using the correctly spec'd die and runout gets better again. Or you might already have the spec, if you're happy with the bushing mandrel you have, order the die for that spec. But you just introduced annealing, so it might take a few loads to get to a consistent spec again.

One more anecdote - when testing a barrel tuner, you WANT bad groups so you can really see how the tuner moves them. So you have to find a bad load to test the one particular thing you're changing. If you shoot one hole at 100, there's no real way other than going really far away to see the changes. If you shoot 3" at 100 yards you can see the tuner swing the group around. You want to see the effects of seating depth, so pick a charge weight that makes bad groups so you can see the group size move with seating depth. When you bring the depth and charge node together, you should have a resilient, long lasting load going forward that doesn't need to be tweaked for a while.

I'm still at odds with finding powder charge at .020 off lands, if I find node at .060 off lands my pressure has increased, will this now effect my es, I'm thinking it will and if it does I may have to change charge and if that happens what's the point of finding charge at .020 off lands.

 

[Kmccord]

I'm still at odds with finding powder charge at .020 off lands, if I find node at .060 off lands my pressure has increased, will this now effect my es, I'm thinking it will and if it does I may have to change charge and if that happens what's the point of finding charge at .020 off lands.

You can try doing a seating depth test at the lowest charge for your cartridge, once you find the sweet spot for the seating depth, then worry about the powder charge.

 

[6pakzak]

You can try doing a seating depth test at the lowest charge for your cartridge, once you find the sweet spot for the seating depth, then worry about the powder charge.

The whole point was to find the charge first according to Eric Cortina and then find seating depth, I do kinda the opposite like you suggest, find depth and then charge but some say, including Cortina, that you are chasing your tail.

 

[Mikecr]

Or he's simply declaring what everybody has been doing for over ~100yrs..
Right? Where is the revolution?

 

[Kmccord]

The whole point was to find the charge first according to Eric Cortina and then find seating depth, I do kinda the opposite like you suggest, find depth and then charge but some say, including Cortina, that you are chasing your tail.

I just do what works for me, Berger also recommended seating depth test first at lowest charge then work on powder charge.

 

[6pakzak]

I guess no one really has an answer on will powder charge remain the same so guess the best answer is to try it out but I don't see powder charge staying the same if length gets shortened quite a bit, book calls for 2.225, .020 of lands is 2.290, it's shooting great at 2.225 but never tried it over 2.250 cause it sucked at that but maybe it will be outstanding somewhere between that and 2.290, I think Ill be chasing my tail, lol.

 

[QuietTexan]

I'm still at odds with finding powder charge at .020 off lands, if I find node at .060 off lands my pressure has increased, will this now effect my es, I'm thinking it will and if it does I may have to change charge and if that happens what's the point of finding charge at .020 off lands.

Is this in your Savage AR? Because there are two discussions here, the theory of how changing seating depth impacts pressure and timing, and the practical of what's actually happening with your current load.

In theory yes, moving a seating depth 0.040" could be enough to make an impact on pressure and muzzle velocity stats of ES/SD. Minor tweaking of 0.010" one way or the other might not push you out of a node.

Sounds like you already ran some loads seated progressively slightly longer from the book COL and groups opened up. This is a small case but also a small bullet, seating depth changes case volume more on large bullets/small cases. So in the specific case of your AR I'm not sure you could move the heavy bullets (70gn+ right?) you're shooting out long enough to feed to get to 0.020" off, so are you trying to do this just to find out? Or would you be ok single feeding to run the load?

 

[LongBomber]

I used to do a powder node first using 20 thou off. Then I ran seating depth testing in 10 thou steps, then finer to tune it in.

Now I just start with 3 thou seating depth steps from either max mag length or the lands (alex wheeler method of finding lands).
I find the spot where I find 2-3 seating depth steps give me the best 100y groups. Then seat in the middle of that and move to powder testing, usually I go from mid-book up to one or two grains over book max in .2gr steps. Stop if I hit pressure.
Most times that will give me a couple nodes, depending on the rifles use I go one down from or the highest node.

I take the middle of the powder node and the middle and +2 thou of the seating depth node. I load up 10 of each and see how they group. Shoot each 10 shot group at 300y. Usually that nets me a solid load.

There are a few things to start with where I agree with Erik's videos. Start with brass in a blue box whenever possible, pick bullets known for consistency.

 

[LongBomber]

I guess no one really has an answer on will powder charge remain the same so guess the best answer is to try it out but I don't see powder charge staying the same if length gets shortened quite a bit, book calls for 2.225, .020 of lands is 2.290, it's shooting great at 2.225 but never tried it over 2.250 cause it sucked at that but maybe it will be outstanding somewhere between that and 2.290, I think Ill be chasing my tail, lol.

The powder charge will most likely stay the same as seating depth changes. At least in the bottle necked cases used in LR stuff. Don't try that in a pistol.
I have shot quite a few ladders changing seating depth and moved more than .1" with no change to the powder charge node.
I have found that es/sd may change, although I am not a fan of the es/sd numbers 95% of guys spout. Not enough shots to mean much most of the time.

 

[6pakzak]

Is this in your Savage AR? Because there are two discussions here, the theory of how changing seating depth impacts pressure and timing, and the practical of what's actually happening with your current load.

In theory yes, moving a seating depth 0.040" could be enough to make an impact on pressure and muzzle velocity stats of ES/SD. Minor tweaking of 0.010" one way or the other might not push you out of a node.

Sounds like you already ran some loads seated progressively slightly longer from the book COL and groups opened up. This is a small case but also a small bullet, seating depth changes case volume more on large bullets/small cases. So in the specific case of your AR I'm not sure you could move the heavy bullets (70gn+ right?) you're shooting out long enough to feed to get to 0.020" off, so are you trying to do this just to find out? Or would you be ok single feeding to run the load?

Actually it is for my bolt gun which I'm shooting 55gr VMAX, crimp ring sits out pretty far at 2.290, I'll probably start .030 out from lands

 

[QuietTexan]

The whole point was to find the charge first according to Eric Cortina and then find seating depth, I do kinda the opposite like you suggest, find depth and then charge but some say, including Cortina, that you are chasing your tail.

There's no single way that works best per se, if it works it works. Some processes are more deliberate though, and use fewer components. It seems like people earlier were talking about parts of the process and not the whole thing though.

I personally have been using:

1. Coarse seating Depth
   1. Typically start at 0.020" off, back out in 0.040" increment (if needed, honestly for comp rifles where I single feed anyways I typically start here and don't do coarse testing unless 0.020" off doesn't work)
   2. Include book COL in the test if it's way short
   3. Look for overall group, specifically horizontal dispersion
2. Charge Weight
   1. Typically shoot at 100-200-300 yards with a chrono
   2. Look for minimal vertical dispersion (hopefully maintaining horizontal)
   3. Look for chrono flat spots
   4. Look for overlaps between the two (change powder here if needed)
3. Fine tune seating Depth
   1. 0.002" to 0.004" increments around the coarse depth (depending on how tight the coarse depth was and far I need to go)
   2. Confirm fine tune seating doesn't wreck the vertical/muzzle stats
4. Tuner
   1. Pick a bad part of the ladder and reshoot to see if the tuner moves the groups
   2. If it does, take the tuned setting and run the load from #3
   3. Tweak if needed

There are different seating depth testing processes being discussed here potentially because there's not a lot of details being provided. As many methods as I can think of off the top of my head in in a minute:

1. Start at X.xxx" off and back up at 0.xxx"
2. Start at 0.000" or some jam and back off
3. The Berger "Big Jump" Method - 4 intervals that are 0.040-0.050" off, then fine tune
4. Start at mag length and back off 0.xxx"
5. Use book COL
6. Seat bullet base to neck junction
7. Seat to a cannelure