Seating depth advice

JohnyRingo

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Jan 20, 2017
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129
Where should I go from here? 300 H&H Mag. 180 grain Accubonds. 67.5 grains of IMR 4831. CCI primers and Nosler brass. 3.652" OAL to lands.

3.585" OAL. ES=100 fps. 1.5 MOA (3-shot group)
3.595" OAL. ES=25 fps. 0.9 MOA
3.600" OAL. ES=15 fps. 0.7 (2-shot group and a big flier)
3.605" OAL. ES=14 fps. 0.8 MOA
3.613" OAL. ES=47 fps. 0.6 MOA
3.625" OAL. ES=25 fps. 1.18 MOA
3.640" OAL. ES=14 fps. 1.15 MOA

Obviously, the 3.613" created the best group. I am surprised it shot so well with the ES being 47 fps. Should I try any other lengths to try to get better than 0.6 MOA? I am kicking around trying 3 shots at 3.610" and 3 shots at 3.620". I don't have a big surplus of reloading supplies to be messing with load development without eating into my supplies a little. This is the first time I have ever messed with seating depths as my other rifles seem to shoot great with advertised OAL. The advertised OAL for this load is 3.600", but I got a huge flier (2") out of it.
 

JohnyRingo

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Jan 20, 2017
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I just did some reading of the Satterlee load development. I am fairly confident that 67.5 grains is my velocity node. I spent a lot of time messing with powder charges. It wasn't until I started messing with seating depths did I get the accuracy under 1 MOA. What I found interesting is that he said he would not go with a load with an ES larger than 30 fps at 100 yards (no matter the accuracy) because of what that would turn into at 600 yards. This is exactly why I am posing this question. The 47 fps ES surprised me.
 

Recon$$

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Maybe try a ladder test with the powder at the 3.600/5 OAL. Personally I find the velocity the rifle likes then mess with seating however, my last rifle I ended up going the opposite route due to the way things worked out. Hardly one of the guys on here that takes it to whole new level but I always get my 1/2 moa load.
 

JohnyRingo

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Jan 20, 2017
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129
Seating depth is just to look for a node or good area. Adjust the powder now to determine the best charge. I'd look at .2-.3 tenths of a grain adjustments.

Based on my data, which seating depth would you go with while adjusting the powder charge?
 

Wolf76

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Jan 5, 2014
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Grandville, Michigan
Based on my data, which seating depth would you go with while adjusting the powder charge?
Anything between 3.605 -3.613 is fine. Take any magazine restrictions into consideration. Seems like you have a wide node(which is great). I suspect you're less than a grain difference from this load to be optimal. FWIW..I consider a solid. 75" moa gun better than one that shoots a couple good groups and then opens up.
 

QuietTexan

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Nov 16, 2020
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Texas
Did you call the flyer before you saw where it landed on the target? If you didn't call the shot as off, and labeled it a flyer after you saw the grouping I'd call it part of the group for the analysis.

Great article, the section on "should we exclude flyers" shows group overlays and why something 2" off might actually be part of the group, even though it doesn't appear that way when there aren't enough data points in the population:
 

7070yshot

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May 26, 2020
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Liberty Hill, TX
Where should I go from here? 300 H&H Mag. 180 grain Accubonds. 67.5 grains of IMR 4831. CCI primers and Nosler brass. 3.652" OAL to lands.

3.585" OAL. ES=100 fps. 1.5 MOA (3-shot group)
3.595" OAL. ES=25 fps. 0.9 MOA
3.600" OAL. ES=15 fps. 0.7 (2-shot group and a big flier)
3.605" OAL. ES=14 fps. 0.8 MOA
3.613" OAL. ES=47 fps. 0.6 MOA
3.625" OAL. ES=25 fps. 1.18 MOA
3.640" OAL. ES=14 fps. 1.15 MOA

Obviously, the 3.613" created the best group. I am surprised it shot so well with the ES being 47 fps. Should I try any other lengths to try to get better than 0.6 MOA? I am kicking around trying 3 shots at 3.610" and 3 shots at 3.620". I don't have a big surplus of reloading supplies to be messing with load development without eating into my supplies a little. This is the first time I have ever messed with seating depths as my other rifles seem to shoot great with advertised OAL. The advertised OAL for this load is 3.600", but I got a huge flier (2") out of it.
How accurate is your powder measurements? .1 .01 or .001 grain?
 

Veteran

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Yep, I second running your measurements from the OGive on the specific bullets you are using to the lands. Use the Hornady or other tool to zero in on the lands, and measure Ogive to lands to measure your jump. I don't think the data you show between 3.595 and 3.613 is statistically different with so limited a data set. It is indicative like someone said that you are in a node range in that area. You will need to shoot some 5 shot groups and fine tune your powder and more seating depth tuning in that one area to really pin down something that is repeatable time after time. You defined a range, now you need to get to something definitive which is repeatable. The 3.613 data with an ES of 47 may even be just a one time fluke? How do you know? See what you get the next few times through. Over the range, I might trust data with lower ES's, but you got to shoot and fine tune to know.
 

Deviant

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Jul 12, 2018
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Nebraska
Seating depth is just to look for a node or good area. Adjust the powder now to determine the best charge. I'd look at .2-.3 tenths of a grain adjustments.
This is completely backwards from most peoples loading process. Do a Berger seating depth test and adjust your seating depth for accuracy using base to ogive not COAL while fire forming brass and once you have that done you do a ladder test and adjust powder charge in small increments to find your node. Once you you have your node go back and do seating depth in .2 increments both directions until you have a perfect load or you start over with a different powder or primer selection. Not saying that this is the best way but thats how most people I know and a few well known smiths have told me to do it and it has worked very well for me with my rifles.
 

Wolf76

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Grandville, Michigan
This is completely backwards from most peoples loading process. Do a Berger seating depth test and adjust your seating depth for accuracy using base to ogive not COAL while fire forming brass and once you have that done you do a ladder test and adjust powder charge in small increments to find your node. Once you you have your node go back and do seating depth in .2 increments both directions until you have a perfect load or you start over with a different powder or primer selection. Not saying that this is the best way but thats how most people I know and a few well known smiths have told me to do it and it has worked very well for me with my rifles.

I missed the part about this being a coal and not a base to ogive measurement. Coal is only useful in making sure it fits in the mag.
I almost always start with the seating depth in crude measurements and then fine tune. Then adjust powder.
 

Veteran

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There are many ways to skin a cat, and many calibers one can kill a deer or elk with, and many different grain bullets, and bullet types that will get the job done. Each person may find one method of another more suitable to their own preferences, and how they are wired. You can use the Dan Newbury OCW method, You can use the ladder test. You can use the Scott Satterlee velocity sill method,
or you can use all three in variants and combinations. Doing a Berger seating depth test may depend on whether you are using Berger VLD's or some similar type of secant point bullet vs. a short blunt bullet, or a regular tangent style shaped bullet. I believe Berger is recommending .04 jumps between bullet seating depths because the Secant style bullets like more jump, and can even work well out to .09, .15, or more jump as opposed to a more conventional .02-.03 kind of jump for other style bullets. Its all part of that
Secant, very long nosed design that cuts drag and makes the Berger VLD's good long range high BC bullets, but does call for more jump than normal bullets in general. In fact I think Berger says or has said in the past, their VLD's are almost insensitive to jump.
You can put'em anywhere you want them and they should still shoot well......not so sure, but I think that's what they have said.
In this case with 180 gr accubonds, a more conventional jump of say .015 to .035 might turn out to be better? So, the jump increments may need to be tuned to that sensitivity range? For hunting, most recommend at least a .02 jump and your magazine length may further dictate what range it has to be in.

I'm also not sure whether you can really home in on bullet seating or fine tune it without having a firm idea of your powder first?
I think selecting your powder and then making sure all the seating sensitivities are run using the same powder makes a lot of sense.
Comparing different seating depths when you are using different powders is like mixing apples and oranges, though there may be some correlation just because your chamber, and barrel, twist rate, and all are a big constant, and a big part of the equation too?

But as to the method you select and how you do it, there are many many ways to get the answer. I just think you have to be as consistent in how you do it as possible. You have to make sure the results are repeatable.

All methods are valid and have valid components that transfer into the other methods too.

Ideally, you'd like to see the OCW method give you the best groups, and show you a Scott Satterlee Velocity Sill at that same Charge Weight (or at the endpoint of the sill) and then run a longrange ladder test at 500 or 1000 yards, that confirms
the OCW and Satterlee sill results at long range. Many like working at 100 yards first just because the OCW and Satterlee tests at 100 yards gets rid of wind and other potential effects that you can see at longer distances. Ie, has a higher certainty.
You can start with the ladder test and work back too, but I sure would want a calm calm day with no wind. Best of Luck to you as you decide what works for you.
 
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