Seating depth vs powder charge ladder tests

[broncman]

I have always wondered how much powder I could burn figuring this out...

So you choose a seating depth to try your powder charges and look for patterns and velocity consistencies. Then you choose a powder load to try for "fine tuning". So you play with seating depth and look for patterns and velocity consistencies AGAIN.....

WHAT IF some of the powder loads you passed over just needed a different seating depth and that changed the whole pattern group all over again!

I was testing some loads yesterday with just seating depth. Went from an almost 100% fill density, bullet off lands to bullet in the lands and same charge. This changed case fill density. Speed started high dropped as case fill changed as bullet was seated longer, then came back as bullet approached lands...

So.....chicken or egg?

A ladder type test for each charge weight with different seating depths.. All overlaid? I need to win the lottery to experiment with all this.

 

[savageshooter86]

I am getting my load finalized using a ladder. I shot at 600 yards at a 20 thous JAM. Worked up to pressure and looked for my accuracy "window". Established my guns safe maximum and found accuracy node at the same time. Now I am going to take the middle charge of that window and try about 4/5 different seating depths to see which the gun prefers. Once I have that, I may go +/- 0.1 gr to see if it tightens. Then if not satisfied may try slightly less and more neck tension

Run a ladder to find node. Run a second to verify(maybe a 3rd) then take that load and shoot for groups with a few seating depths.

 

[WyleWD]

What caliber rifle, barrel, length & Twist rate? Hunting rifle or target rifle? Scope type and magnification?

It is a good practice to run a ladder, but I've got a rifle right now that I ran 4 ladders on that it still shot in the virtually the same hole at 200yds in spite of a 1.5gr spread (5 loads at .3gr increments) on powder on 2 different powders and two different primers. So it is tough in that instance to come away with any real concrete conclusions.WD

 

[broncman]

Just playing the devils advocate a little.... IF nodes are velocity and pressure dependant, then when you change seating depth , HOW do you know that one of the powder charges you skipped over for the final tuning would not exhibit better accuracy from a seating depth change that you never tried ?

You picked a load by varying powder for a CERTAIN seating depth!
Or you can pick a load by varying seating depths of a CERTAIN powder load??

Both powder and depth change velocity. Chicken or egg so to speak when you get near case capacity etc...

So you have 2 different type nodes....

Vary the powder in relationship to same seating depth...
Vary the seating depth in relationship to same powder charge...

If one could test the possibilties of both approaches and graph the results, would the nodes overlap? Be the same?

 

[BoydAllen]

Working on the premise that accuracy nodes are "velocity specific" I would think that it would be interesting to record velocities of a powder charge workup at a single seating depth, note any velocity changes that are associated with changes in seating depth at a promising powder charge, and then do a test where any velocity difference was adjusted out by charge as step three. Do any of you have velocity data from changing seating depth and leaving charge constant? I would think that the biggest difference would be when going from seating into the rifling, or touching, to jumping bullets, but that is only a guess based on old reloading manual info.

 

[broncman]

I actually do have some limites data from my last barrel when I chronod same powder charge but different depths. My new barrel is broken in per Shillens recommendations. No more shots than their procedure so I got a great test bed! I chronod most of the shots during breakin.

I have about 3/4 grain spectrum that gives me acceptable velocity for the 215's before I am seeing pressure signs.


Soo... Gonna load 5 round groups in .2gr increments and a 5 rd group for .005 from lands, .010 and .015 in each powder charge. So that will be about 75 rds. One days worth of match ammo.

Gonna chrono each, catalog and use same poh for each one. Then compare targets and scan each one. Interesting to see the results I get.

 

[Lapua40X]

One of the greatest thrills of reloading is trying every conceivable combination of load/bullet seating arrangements and never being perfectly satisfied with any of the results; always seeking that elusive perfect combination. It's expensive but it sure is fun.

 

[jelrod1]

I've always thought of initial load devlopement as finding the middle of a node with all loads the same seating depth, fairly close to where I think I'll end up. The thought is that tuning depth afterward will still keep you in that and not have to find another. If initial work puts you on the edge of a node I could see where you might come out of it with further tuning.

 

[WyleWD]

Do any of you have velocity data from changing seating depth and leaving charge constant? I would think that the biggest difference would be when going from seating into the rifling, or touching, to jumping bullets, but that is only a guess based on old reloading manual info.

I did this very test on my 6xc just 3 weeks ago. Not a cloud in the sky, and done at 10:30 in the morning. Varied the depth from a soft jamb, just short of the lands, 3 thousandths off, 6 thousandths off, and 10 thousandths off. The average velocity only changed approx. 5 fps. from 10 off to soft jamb.

I found what I was looking for when I used just short of the lands, left the charge etc, the same and changed primers. WD

 

[BoydAllen]

Interesting...define soft jam, if you don't mind.

 

[6BRinNZ]

broncman - I think mikecr proposes that seating depth has a larger impact than powder % change and if I understand correctly he actually works on seating depth for best accuracy first.

I don't understand finding a powder charge, then a seating depth then tuning again with powder charge change....wouldn't the final powder charge change have just altered the harmonics and changed the "window"...maybe not?

 

[broncman]

Hopefully my test will create a map that will show those relationships. Working with a process engineer who is going to help me plot all the data I collect into several landscape type maps. Hopefully I can use these maps to overlay velocity data, accuracy, length and charge relatiinships.

I use these type data maps at work to track all kinds of machine, production, availability, and cause code data.

 

[savagedasher]

Here is a test I just tried with Quick load 6mm dasher case ol 2.400 100 % fill 2854 fps
2.402 99.9 % 2853
2.404 99.8 % 2852
Good Shooting Larry

 

[savagedasher]

Here is more play only with 90% fill 2.400 2585 2.404 90.1% 2584 so if the neck is being used it changes half. Good Shooting Larry