seating depth question

S

Shadow9mm

New member
I am getting ready to do the berger seating depth test to find the sweet spot for a bullet. Does the same bulelt in the same gun always prefer that specific seating depth? how would changing powder or charge weight affect the seating depth? i wanted to check velocites and find a plateau in the curve to help keep my groups consistent but i will have to fine tune powder after seating depth due to the changes in seating depth affecting the velocities due to changes in case capacity and distance from the lands.
 
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how would changing powder or charge weight affect the seating depth?
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That would be up to you. And what you want the rifle to do with the ammo.

If I reading your intent correctly, you've asked half a question, which has a full answer, but not the answer I think you are looking for.

how would changing powder or charge weight affect the seating depth?
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I does not. Powder type or charge weight has NO EFFECT on the seating depth. Mechanically.

But, changing them might have an effect on where you WANT to seat the bullet. And this depends on what your rifle does.

It seems you are not loading to a set COL with a given bullet, but looking at "chasing the lands" seating to various distances off the lands, looking for the best groups you can get.

This is a different situation from "normal" reloading where a given bullet is loaded to a certain COL consistently. Bullets loaded to the cannelure, for example, will always have a consistent seating depth.

You're going to do a test looking for a sweet spot with a certain bullet. Fine. You've got a load picked out to use, no doubt. Fine. Use that load, and change ONLY ONE thing (seating depth) and you get useful results.

Change two things and you don't get useful results, very often, because you don't know which changes did what.

Change the powder type, or the charge weight of the powder you are using, and you have changed conditions and you have to start you series over.

When you are searching for that "n th degree" of accuracy EVERY change could be the one that improves your group, or possibly screws it up, and the only way to find out what the change does, if anything, is to shoot them.
 
Absolutely correct. If you leave your home and drive north for 10 miles, then drive south for 10 in your neighbor's car to arrive home again, what have you learned about your car?
 
44 AMP said:
That would be up to you. And what you want the rifle to do with the ammo.

If I reading your intent correctly, you've asked half a question, which has a full answer, but not the answer I think you are looking for.



I does not. Powder type or charge weight has NO EFFECT on the seating depth. Mechanically.

But, changing them might have an effect on where you WANT to seat the bullet. And this depends on what your rifle does.

It seems you are not loading to a set COL with a given bullet, but looking at "chasing the lands" seating to various distances off the lands, looking for the best groups you can get.

This is a different situation from "normal" reloading where a given bullet is loaded to a certain COL consistently. Bullets loaded to the cannelure, for example, will always have a consistent seating depth.

You're going to do a test looking for a sweet spot with a certain bullet. Fine. You've got a load picked out to use, no doubt. Fine. Use that load, and change ONLY ONE thing (seating depth) and you get useful results.

Change two things and you don't get useful results, very often, because you don't know which changes did what.

Change the powder type, or the charge weight of the powder you are using, and you have changed conditions and you have to start you series over.

When you are searching for that "n th degree" of accuracy EVERY change could be the one that improves your group, or possibly screws it up, and the only way to find out what the change does, if anything, is to shoot them.
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Ok took some time to think over it. I reload for 223 but have never gotten to tinker with seating depth due to magazine length restrictions. My new hunting rifle in 30-06 has a lot more room for playing with seating depth. I am coming at this from a bullet oriented standpoint, pick a bullet for a specific use, and get all the potential out of that bullet in my gun that I can. for example .308 150g Hornady Interlock Boat Tail for white tail deer. I was planning on a 3 stage testing process.
1: testing bullet seating depth for best accuracy with starting load
2: test a powder/primer combo to max for safety
3: take safe max load and work 2g down back up to max to check for a flat velocity
node for best ES
4: repeat steps 2 and 3 with the same bullet and seating depth as needed.

I was just trying to understand bullet seating depth. I was hoping like i said, each bullet would have a ideal seating depth window in my gun. That would allow me to work up a powder load independent of seating depth, making things a lot less complicated.
 
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If I’m reading your process correctly I don’t think you need step three because you can do that in step two along with the things you’re doing in step 2 just shoot them through a chronograph while you’re doing step two .

Although not the same I have a similar thread going here and I believe unclenick said something about his experience is once you find a good seating depth for bullet A it will tend to like that seed in death regardless of the other components used .

https://thefiringline.com/forums/showthread.php?t=607383
Unclenick said:
…..., I find the seating depth that is best for one load often turns out to be best for others with that same bullet (or sometimes a number of bullets), so I now look for that minimum group first, then try tweaking barrel time. At first, I assumed it would always work best to match barrel time, but for some reason, it isn't always so. The barrel time that is best can shift a bit with bullet seating depth, and I am not sure why. It may be the difference in timing with which the chamber starts to stretch as the bullet enters the lands, initiating a pressure wave pair. All I can do is running a second ladder after finding the best seating depth to see if it finds you a better sweet spot or not.
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If I did understand that correctly your idea of finding seating depth first with lower charge then working the load up seems like it might be a good idea . However I’m not sure I like the idea of doing that at the minimum charge . Only because it’s possible the minimum charge does not expand the case fully and I think I’d want all the internal ballistics to be the same as they likely will be with the final charge so I'd like my testing pressures be a bit higher then start loads

I think I’d load two rounds each in half grain increments from minimum to about halfway up the charge spectrum . If you don’t see any pressure signs all the way up to that final middle charge that middle charge is where I would do my seating depth test . the only problem I see is where are you starting the seating depth and which direction are you going to move the bullet ?
 
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Metal god said:
If I’m reading your process correctly I don’t think you need step three because you can do that in step two along with the things you’re doing in step 2 just shoot them through a chronograph while you’re doing step two .

Although not the same I have a similar thread going here and I believe unclenick said something about his experience is once you find a good seating depth for bullet A it will tend to like that seed in death regardless of the other components used .

https://thefiringline.com/forums/showthread.php?t=607383


If I did understand that correctly your idea of finding seating depth first with lower charge then working the load up seems like it might be a good idea . However I’m not sure I like the idea of doing that at the minimum charge . Only because it’s possible the minimum charge does not expand the case fully and I think I’d want all the internal ballistics to be the same as they likely will be with the final charge so I'd like my testing pressures be a bit higher then start loads

I think I’d load two rounds each in half grain increments from minimum to about halfway up the charge spectrum . If you don’t see any pressure signs all the way up to that final middle charge that middle charge is where I would do my seating depth test . the only problem I see is where are you starting the seating depth and which direction are you going to move the bullet ?
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I was planning on using the berger seating depth test for hunting rifles. shoot 2 groups of 3 at the listed distances off the rifling. one group is supposed to out shoot the others. then work .002 or .005 up and down from the one that shoots well to fine tune it.
off the lands
.010
.050
.090
.130
The idea of testing seating depth half way up makes sense.
https://bergerbullets.com/getting-the-best-precision-and-accuracy-from-vld-bullets-in-your-rifle/
 
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