I personally start a couple grains under book max and load starting at .020" from lands .003" increments going deeper until i find seating depth then fine tune through powder charges going up in .2-.3gr increments while watching for velocity node and signs of pressure. Seating depth is the macro adjustment, powder charge is the micro. Remember your case capacity/combustion changes with seating adjustments
Which comes first, the chicken or the egg? Charge weight or seating depth…
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If your gun doesn't like a particular powder, no seating depth will change that. The right powder for your particular gun and bullet combo makes all the difference in the world. Seating depth for me is only a fine tuning process.
I'd also add that Brian Litz knows what powder will be more forgiving already and seating depth is all fine tuning from that already forgiving starting base, which is the right powder and bullet combo for a particular gun.
The two rifles I shoot for long range I've had for several years over that time I know what seating depth will shoot, so I'm normally pretty close with that in which case I start working on a powder charge then fine tune with seating depth again
Wolf76
Well-Known Member
IME... the ideal seating depth doesn't change with powder or powder charges. This is why I start with this half of the equation. I can very quickly identify powders or charges that show promise.
I'll start .010 off the lands, and work rough increment charge weight first. Then rough increment seating depth. Then a finer tuning pass on charge weight, and a finer tuning pass on seating depth. Then primer seating depth testing in 1 click increments on the CPS. Then if I'm still not happy, I'll work with seating depth one final time.
Here's my experience and 2cents worth. Changing the powder charge changes velocity thus changing how and when the bullet contacts the rifling. I first find the best accuracy node by adjusting powder charge. Then I load up 50 of those rounds at a seating depth .005" off the rifling. At the range I have a single stage press with a Forster micrometer seating die installed in a rig that slides into my trailer hitch receiver. I shoot a 5 shot group write down the results along with that seating depth. Swab out the barrel, (not a cleaning, all my rifles shoot better when dirty) Next 5 I change the seating depth to .010" then repeat through all 50 rounds. changing seating depth in .005" increments. I pretty quickly see the groups tighten up really nicely at around .020". I use this method for 30-06, 308, 270win and 243win. I've never had to go through all 50 rounds. When I hit the seating depth that gives the best results I seat all the remaining rounds to the newly discovered seating depth. Keep in mind that it is the ogive that contacts the rifling, not the tip. Changing bullets types/manufacturer will necessitate changing the seating depth.
Powder first, seating 2nd, then powder again if seating changed
I find long range and benchrest are two different things and are tuned slightly different because the chamber dimensions are more precise with BR. The smallest ES/SD are what you are initially looking for. There are usually two nodes that will show small ES/SD. Choose the node with the highest speed as long as you don't see any pressure signs. I also start with the factory recommended CBTO measurement for seating depth and fine tune from there.
An ES/SD greater than a single digit really starts to show up when you get past 800 yards has been my experience depending on the caliber and bullet choice. This is especially true in the vertical since the horizontal has more to do with reading the wind. If you have a double digit ES/SD it becomes a crap shoot trying to guess both the vertical and horizontal dope to come up with a shooting solution.
An ES/SD greater than a single digit really starts to show up when you get past 800 yards has been my experience depending on the caliber and bullet choice. This is especially true in the vertical since the horizontal has more to do with reading the wind. If you have a double digit ES/SD it becomes a crap shoot trying to guess both the vertical and horizontal dope to come up with a shooting solution.
Yup! X2
PNWdude67
Well-Known Member
The first thing??? Neither seating depth or powder charge, I start with consistent neck tension and maintain that throughout the life of the brass with annealing and the case prep process. We don't clean primer pockets or get OCD about case weight, sorting bullets etc. We do trim and use an expander mandrel after annealing and full length sizing every firing to get as consistent neck tension as possible. Then find a moderate velocity node with a generous jump of at least .025 or .050 (maybe more) and can usually run it for the life of the barrel increasing powder charge as needed to stay at speed.
I know you can do it either way, and I started out finding charge weights first and then doing bullet seating depths, but I have come to believe two things. Its going to depend. What I think it depends on is 1) the specific rifle and chamber cut in that specific rifle
2) the bullet shape and type/design. Some rifles are going to be more sensitive to seating depth depending on their chamber set up and the type and design of bullet. So for example seating depth on Berger VLD's and seating depth on Sierra Gamekings or Lapua Scenars, or a blunter nosed type bullet may be very different in different chambers, but not vary so much by charge weight.
(You can vary charge weights and powders all **** day on a bullet your rifle hates, and you will just get mad and madder....)
I think now, it makes more sense to me to pick a charge weight 7-8% below max load area, and figure out a good seating depth for a specific bullet type and design and weight with a powder that's one of the known go to's for that caliber. Maybe in grosser larger seating depth changes like .01-.02 increments. Yes, and even try some different bullets in this phase too.
Then fine tune with different powders and charge weights, and then maybe come back to bullet seating and fine tune with
very small changes one more time, but making .005 kind of changes to bullet seating depth this time.
Change in bullets, design, weight, type, means re doing all this to some extent.
Now, if you are an F Class shooter like Brian Litz and you pretty much know your bullet type, design, weight, etc.
And its not going to change much for hunting, or other shooting, maybe you start with charge weight and powder and
narrow that down, then fine tune the bullet seating depth. Like I said, it can work both ways, but its somewhat dependent on what your rifle design is, what your goals are, and what your bullet design, and types are, and what your goals will be. That's just what I believe at this point in my own learning.
2) the bullet shape and type/design. Some rifles are going to be more sensitive to seating depth depending on their chamber set up and the type and design of bullet. So for example seating depth on Berger VLD's and seating depth on Sierra Gamekings or Lapua Scenars, or a blunter nosed type bullet may be very different in different chambers, but not vary so much by charge weight.
(You can vary charge weights and powders all **** day on a bullet your rifle hates, and you will just get mad and madder....)
I think now, it makes more sense to me to pick a charge weight 7-8% below max load area, and figure out a good seating depth for a specific bullet type and design and weight with a powder that's one of the known go to's for that caliber. Maybe in grosser larger seating depth changes like .01-.02 increments. Yes, and even try some different bullets in this phase too.
Then fine tune with different powders and charge weights, and then maybe come back to bullet seating and fine tune with
very small changes one more time, but making .005 kind of changes to bullet seating depth this time.
Change in bullets, design, weight, type, means re doing all this to some extent.
Now, if you are an F Class shooter like Brian Litz and you pretty much know your bullet type, design, weight, etc.
And its not going to change much for hunting, or other shooting, maybe you start with charge weight and powder and
narrow that down, then fine tune the bullet seating depth. Like I said, it can work both ways, but its somewhat dependent on what your rifle design is, what your goals are, and what your bullet design, and types are, and what your goals will be. That's just what I believe at this point in my own learning.
