Which comes first, the chicken or the egg? Charge weight or seating depth…

[Veteran]

By the way, for those who believe that differing powders or powder charges have no bearing on the ideal seating depth, if your
think about Chris Long's theory and his paper on barrel timing, and harmonics, I think the only conclusion you can come to is that
powders, bullets, and rifles are all one system, and they all have to work together to make the load a precise and accurate load in that specific rifle. It all matters. There are optimum combinations of powder and bullets, and seating depths for that specific bullet that work best in certain specific rifles with certain chamber set ups and barrel length, and barrel diameter that minimize harmonics
to optimize accuracy and precision. Its a total system that has to be tuned, not just the bullet or the bullet seating. It all matters
and has to harmonize together.......but maybe I should not use the word harmonize cause harmonics are bad by definition....

 

[QuietTexan]

I don't think there's one sure way to skin this cat, depends so much on what exactly you're doing and looking for.

I didn't see anyone has said anything about being length restricted yet, so if I'm limited by that then I start at either book COL, max mag length, or the cannelure Hornady puts on the SSTs, and do a powder ladder.

My most recent development plan was a 50-round test that was a mini-ladder from my starting charge to 93% max charge, then a 30 round seating depth test, then a powder ladder at the best depth (mini-ladder and full ladder were 20 rounds total). I was not looking for two things from this - max pressure and max velocity. Just a nice good shooting load to hit steel with, and it doubles fine for hunting pigs out to 800 yards. This was a powder I'd used in the case before.

My plan for Hammers is to set the COL at the last PDR, and run several different powders looking for pressure.

Last year on a 300 RUM with Berger VLDs and Nosler ABLRs I did seating depth testing first, and there was some serious group size differences on the seating depth, especially the ABLRs. The difference was drastic enough that starting at 0.020" off the lands with that bullet would have been a fool's errand. Nosler notes to jump the ABLR on their page, and sure enough book COL was were it ended up.

My plan for my new range rifle barrel (6.5-284 in a long action, so should be no OAL limit) is test a couple powders at 0.020"-ish off the lands, then do depth then back to powder, then all the other variables. And probably won't stop changing things until the barrel is done since this will be my first time out with this cartridge.

 

[Barrelnut]

With a cartridge or bullet new to me, I do seating depth first. Reasoning is that large changes in seating depth can affect the powder charge. Especially using powders that can fill the case close to 100%. For me, seems I usually find low SD/ES when the case is close to full. So I want to know seating depth first. If you work up a charge and then suddenly find the best seating depth is .050 deeper, that can affect pressures too. Or you may not discover that a .050 works great because you can't seat the bullet that deep cause you have too much powder in the case already.

 

[WestSoDakThwack]

I have all factory chambers, so it seems mag length becomes an issue before i get to what many would like to see for seating depths/distance to the lands. Generally i start with a coal that "should" function properly from which ever mag the rifle uses, and then attempt to find a charge/powder combo that gives the results im looking for. Many times i just plan on loading to mag length and working around it and never doing more with seating depth.

 

[Creedmoor shooter]

Usually I'll find what my max pressure is for the particular bullet and powder I'm trying to use is in my rifle. Once I find that I back off 1grain and go into seating depth. I'm a firm believer seating depth has the most effect on your groups than powder charge. Once I get the happy spot for seating depth I'll then get into powder charge if necessary. Most of the time I can tune a load with seating depth alone.

 

[epags]

Here's my experience and 2cents worth. .......... 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.

Corrected my questioon ... replaced COAL with CBTO which I had meant in the first place....another senion moment. Having a senior moment and for my age that is not a suprise. Question: If you measure the CBTO off the ogive of bullet A and it works best with a (say) 0.04 jump, why wouldn't the same CBTO off the ogive of bullet B work equially well? The jump is still the same.
Question 2. I thought the Hormady tool measured from the ogive to the base. It that an erronious thought.

 

[QuietTexan]

Because the tool you're using to measure CBTO off the meplat is not necessarily the same distance from where the bearing surface engages the rifling for different bullets. If you're using the Hornady tool or something similar you aren't measuring the actual engagement point, you're measuring a distance in front of that point based on the size of the hole in the tool. It will b e the same for a given bullet, but a different profile will measure differently.

 

[Veteran]

Even if measuring Ogive off lands to Ogive off lands for different bullets, seems to me it could go either way.....

For very similarly constructed bullets with tangent profiles, or with secant profiles, maybe you are close enough the rifle doesn't care.
But what if one bullet is a blunt nose bullet with a different profile and total length (yet same weight in gr) and it has very different firictional profile going down the barrel or it has different center of gravity or both vs. the other bullets. You may get different performance results depending on all the different characteristics of a specific bullet vs. another. I do think its much much better to be measuring Ogive to lands and setting up your seating measurements that way, but when you switch bullets I think you better check the seating and performance test them to see how close or far from your assumptions are from a different bullet that worked well with a certain seating. Maybe seating is much the same, maybe not.

 

[misterc01]

Powder Charge. Seating depth at about .01 thousandths then test shots. When I settle on a powde r harge. then I start testing seating depths.

 

[Pdyson]

A few years ago I switched to the 10-shot load development process. I knew that these new VLD bullet shapes (especially Berger) liked to be close to or into the lands. However some of my fav cartridges are restricted by magazine length. So I just checked my charge weight/ primer combination at magazine length. Once I found a low ES SD powder/primer combo I would adjust seating depth going shorter than mag length by 3-thou increments. However if they grouped really loose from the start, I'd chose a different bullet and start over.

 

[OrionsStar]

I start about .20 off and do a coarse seating test. Then find pressure, then ladder for a node and check groups at the best nodes including ES/SD. I may or may not try a different primmer at this point or if it looks like poop I change powder. Then I do a fine seating for fine tuning. Stay in the nodes with velocity. I bump seating out sometimes to stay in node to see if groups improve or not if I have too.

 

[FEENIX]

I start about .20 off and do a coarse seating test. Then find pressure, then ladder for a node and check groups at the best nodes including ES/SD. I may or may not try a different primmer at this point or if it looks like poop I change powder. Then I do a fine seating for fine tuning. Stay in the nodes with velocity. I bump seating out sometimes to stay in node to see if groups improve or not if I have too.

Really, .200" off the lands as your baseline seating depth?

 

[QuietTexan]

Question 2. I thought the Hormady tool measured from the ogive to the base. It that an erronious thought.

The Hornady tool is not the most precise thing ever made. That's why the whole set of them costs less than a single comparator from SAC. The hole on the 6.5mm Hornady tool is going to be something like 0.250", even though a 6.5MM barrel is .264" across the bottom of the grooves, and 0.256" across the lands. The bullet will interface with the lands somewhere between those two measurements depending on how the reamer cut the chamber, but the tool does not measure that exact point. The tool measures some arbitrary distance in front of that point which is consistent enough for a single bullet, but doesn't work across different models of bullets. The SAC comparator notionally does measure the interface point by using a 3° angle between 0.256" and 0.266" to mimic a chamber, but then there will still be a difference between the tool and what the eroded throat of a particular rifle looks like. It doesn't matter so long as you measure the seating depth of each different bullet you load on your tool.

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Typos aside, in my 300 RUM seating a Berger 210 to the generic book COL in the manual of 3.600" is a jump of 0.229". I seem to recall Berger having a caveat at the front of the book about testing seating depths though Touching the lands is basically 3.900" COL.

 

[nksmfamjp]

Question 2. I thought the Hormady tool measured from the ogive to the base. It that an erronious thought.

No, it measures CBTO. I'm not sure that tool brand to tool brand or tool to dwg can be compared.