Seating depth node?

[OkieMike]

I wasn't sure how to phrase the title... So I just went with what is there.

Same rifle. Same brass. Same bullet. Same primers...

2 different powders... with a significant difference in charge weight and resulting velocity... But both are showing a trend of good groups at the same seating depth.

I didn't plan it that way. I just happened to notice a correlation while studying targets from different range trips.

Now, it is the same bullet. So it stands to reason that, at least theoretically, a given seating depth would work no matter what... But I really figured a 250 fps difference in velocity/pressure would change that.

Is it a fluke or is there something there?

Mike

 

[rijndael]

I have a couple of loads that work well across multiple powders at the same seating depth.

 

[kthomas]

Or plot twist: seating depth "nodes" don't actually exist....

 

[OkieMike]

Or plot twist: seating depth "nodes" don't actually exist....

Perhaps they don't. Maybe I just found the "sweet spot" that these bullets like in my gun.

I just called it a "node" for lack of a better description.

Mike

 

[bax]

Maybe it just accidently worked out that way. Dumb luck works too.

 

[OkieMike]

Maybe it just accidently worked out that way. Dumb luck works too.

I need to do a bit more testing before I can conclude it's a success... But no matter whether it's luck, science, or magic... I'll run with it if it works.

Mike

 

[Brentc]

It has nothing to do with luck. I've observed the same thing multiple times. Once you find a seating depth sweet spot with a particular bullet, it usually stays the same when testing different powders.

 

[russkim04]

Agreed with others on A bullet having a seating depth node. I've heard of this before from others also

 

[Aftermath]

What seating depth is actually doing...actual node or just pass/fail?

Not sure where to begin...but jump testing is something we all see a lot, and it typically the discussion goes back to bullet timing/barrel vibrations/etc...along those lines. one thing that has always hung in my mind is "forgiving" bullets...how are bullets "forgiving" if the whole idea of...

www.snipershide.com

I'm in the "it matters" camp.
My experiences, especially with the VLD, is that there is a distance from the lands that is better. That distance may very well be pressure related, too. I like to have the bullet traveling as fast as is safe...safe pressure. I start with bullets just barely off the lands and increase charge weight to find where I get pressure. Then I back off the charge so there is not any signs of pressure. Then I start seating the bullet deeper in 0.002" increments. I've always found a depth that shoots better.

 

[Brentc]

There is a load development method (Berger) based on this very idea. The method includes starting with seating depth testing at safe starting loads. Once you've found the best seating depth, you then work your powder charge for best performance. This method assumes that once you've found the sweet spot for seating depth, everything else can change but the seating depth remains the same.

 

[Aftermath]

There is a load development method (Berger) based on this very idea. The method includes starting with seating depth testing at safe starting loads. Once you've found the best seating depth, you then work your powder charge for best performance. This method assumes that once you've found the sweet spot for seating depth, everything else can change but the seating depth remains the same.

Yes. Once I find that seating depth, I then increase charge again looking for pressure signs and to see if I can squeeze more velocity out of the system. Pretty much can always get more velocity but usually at a loss of accuracy. I'd guess that about 80% of the time, that first go is the one I stick with.
Now...if components were more readily available, after finding that new pressure spot at the nice seating depth, I would adjust the seating depth again to try to find another at the increased velocity.
At the cost of barrel life.
It's all a bit of a trade off.
That first go around usually takes me about 100 rounds. I will have 100 fire formed cases and I'm dialed in for the life span of the barrel, pretty much, because once I find the CBTO, I don't chase the lands and I generally never try a different powder or bullet. If I want to shoot a different bullet, I grab a different rifle haha!

 

[OkieMike]

Thanks for all the replies.

I've got 4 rounds loaded at the (hopefully) magic seating depth and will test it as soon as I get a chance.

Normally I do 3 rounds but there was one primer left in the tray and one piece of brass left that had been fired one less time than the rest... So this will be a 4 round test.

This hobby is addicting... It's like solving a puzzle. The anticipation is killing me.

Mike

 

[Aftermath]

@OkieMike where in OK are you? I'm in Stigler, have family around Vinita.

 

[OkieMike]

@OkieMike where in OK are you? I'm in Stigler, have family around Vinita.

PM sent

Mike

 

[JAS-SH]

I wasn't sure how to phrase the title... So I just went with what is there.

Same rifle. Same brass. Same bullet. Same primers...

2 different powders... with a significant difference in charge weight and resulting velocity... But both are showing a trend of good groups at the same seating depth.

I didn't plan it that way. I just happened to notice a correlation while studying targets from different range trips.

Now, it is the same bullet. So it stands to reason that, at least theoretically, a given seating depth would work no matter what... But I really figured a 250 fps difference in velocity/pressure would change that.

Is it a fluke or is there something there?

Mike

Too many unknowns here. Impossible to tell with the limited information you have provided.

Forget groups for a moment. Which caliber? Calibers all behave different;y. Powder variables from switching powders alone can make huge differences in internal ballistics performance. A variation of 250 fps is suspect and might be dangerous. Different burn rates. Different powder case volumes. All of those are important variables that affect internal pressures.

Even different range days, especially in the winter where we have more temp and pressure variability.

Hope the seating depth is not too close to the lands. The closer to the lands, the less safety margin for error.


.

 

[Pat Jennings]

@OkieMike where in OK are you? I'm in Stigler, have family around Vinita.

I'm over the line in Goodman Missouri. My son is in Jay. He runs the emergency services there.

 

[Chickentoast]

I've also experienced the same: for a given barrel and projectile, there is a seating depth that works best, even loaded light or with a different (but appropriate) powder.

Also echo my favorite part of shooting is setting up and figuring out the multi-variable equations that yield our results.

 

[OkieMike]

I'm over the line in Goodman Missouri. My son is in Jay. He runs the emergency services there.

Years back I sold my furs over around Goodman.

Mike