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Thread: Bullet seating depth numbers - did I do this right?

  1. #1
    Member jmg's Avatar
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    Default Bullet seating depth numbers - did I do this right?

    I am loading my first batch of rounds, 200 grain Nosler Partitions in 30-06. I have gone through a number of processes for measuring cases, bullet seating depth, etc. and just want to run numbers by everyone here out loud before I actually load everything down with powder in the cases. I have used various data from both the Lee manual that came with my loading kit and I have the Nosler loading manual as well. I trust the Nosler manual a little more just because the Lee manual is not bullet specific.

    First up, cases. Both Lee and Nosler manuals have the distance from the head to the first point on the shoulder at 1.948", and to the other end of the shoulder at 2.109". This tells me that my headspace gauge, which I am using the Hornady gauges on a digital caliper, should run somewhere between these numbers, 1.948" – 2.109". I also have a Lyman headspace gauge, that does not really measure anything, you just put the case into it and verify it is at least within SAAMI specs.

    What I did is I went to the range and I shot off about 40 rounds, in three different bullets. I shot Barnes X, Winchester Super X, and some super-cheap-on-sale PPU rounds. I measured every case with the Hornady headspace gauge to see what the headspace is for a fired round in my rifle. The Barnes and Super X all measured at 2.0385", and the PPU mostly measure right around 2.039", with one of them coming in at 2.040. Based on this data, I decided I would adjust my resizing die to 2.0385" so that I know I didn’t go too far out on the headspace. Once the dies were adjusted, I resized 25 cases to this spec. I then cut all of the cases to length with the Lee case length gauge specific to 30-06, and then chamfered/deburred the case mouths, and then double checked each case in the Lyman gauge as well.

    Next up, figuring out seating depth for this specific bullet. I’ve done a couple of different methods here to figure out my distance to the lands. First, I took a fired cased, slightly dented the mouth and then set a bullet into it. Then, I slowly and gently put the round into the chamber, and closed the bolt slowly. I then carefully withdrew the round and measured it with the Hornady bullet comparator. This tool effectively measures to the ogive rather than cartridge overall length. The measurement I got with this method came to 2.778". I believe this means that 2.778" is my distance to the lands at the ogive for this particular bullet under this particular test.

    I then did another test. I inserted the bolt and closed it down in the chamber without dry firing it (firing pin is back). I then took an old piece of fishing rod blank (was going to go get a dowel rod but I had this around already instead) and ran it up the muzzle to the bolt. I placed a clip on the rod right at the muzzle so that it was flush with the muzzle.

    Then, I removed the bolt from the rifle and inserted a bullet without a case into the chamber. It dropped to the lands, and I held it there with a long screwdriver against the lands. I then took the fishing rod blank and ran it up the muzzle again until it hit the tip of the bullet. I then placed another clip right at the muzzle. I now had two clips on the rod which to measure at. The problem was I would be measuring from the outside of one clip (the bullet clip) to the inside of the other clip (bolt clip). So I took a third clip and set it right up flush against the bullet clip, so now I had two clips to measure the inside distance on. That distance came to 3.276” – this, I believe, would be my COAL if I placed the bullet right up on the lands.

    One I had this COAL for this specific bullet, I then seated it into a dummy case at this exact distance. Then I measured it with my Hornady bullet comparator as I had done earlier, to the ogive. I got 2.665” under this test. This is different than I got on the test above where I simply pushed a bullet that was snug in a case into the chamber, as that was 2.778”. But, this is essentially off by only .013”. I feel like this amount of difference could come in having pushed the bullet further into the lands in one test over another, my replacing clips in the second test, etc.. It seems to me that the test where I pushed a cased round into the chamber could have pushed the bullets into the lands by this much, as opposed to the bullet “just touching” the lands on the second test. I don’t feel like .013 here is a significant amount. My plan was to seat this bullet .020 - .030 off the lands anyway. If this .013” is a significant amount, please let me know, and please let me know how to get a more accurate reading?

    So this is where I am at. My plan is to seat the bullet so that on my bullet comparator it comes in at 2.750" at the ogive. This would put it off the lands .028" under the one test I did, and .015" off the lands under the second test. This should give me a COAL of 3.261”. Should I go any further than that? Maybe another .005" so that I am at least .020” off the lands in the second test? This would only be .033” off the lands from the first test. By the way, I did measure my magazine length, which is 3.372", so no matter which way I go above, my rounds will fit and feed from the magazine just fine.

    In comparison, a factory 220 grain Remington Core Lok on my bench measures at 2.746" to the ogive, and has a COAL of 3.250". Obviously a different bullet, and set to SAAMI specs by the factory, but I feel like I am close to on par with where I need to be.

    The only thing that even makes me hesitate on these numbers at this point, besides the .013" difference in my two measurements to the lands, is that my Lee book says that my minimum COAL on a 200 grain jacketed bullet should be 3.295” when using RL 19 powder (which I am). My COAL is going to be significantly less than that - .034" under. I am not sure this is a significant problem because I think the Lee book covers all bullets, and my understanding is that this distance can change dramatically by bullet because of design, ogive distance, etc.

    So, at this point, my plan is this:

    1. Resize cases to 2.0385” on the Hornady headspace gauge, and then double check all cases with the Lyman gauge to verify they’re within tolerances. Then cut mouth with case length gauge.
    2. Load three cases with 52 grains of RL 19, and then 3 more cases each at .5 grain intervals up to a max load of 56 grains, per the Nosler book data.
    3. Seat the 200 grain bullets at 2.750” to the ogive on my bullet comparator, which should give me a COAL of 3.261”.
    4. Go out and do round robbin shooting on all of these, checking for pressure signs, to find the most accurate load. Then maybe play with the seating depth after that?


    Does anyone see any issues with anything I’ve done here, something I’ve missed, something I should have done differently? Should I seat bullets in step 3 at 2.745” instead of 2.750”?

    I know this was a long post, but this is my very first batch of loads that I’m putting together and I really don’t want to mess up my rifle, or, well, blow myself up. I've read my loading manuals, many websites, including here, to learn all I can about this hobby so I can be as safe as possible. If you’ve made it all the way to the end here, you are awesome, and thank you so much for any assistance or advice you can provide.
    Never count your days, but rather, make all of your days count.

  2. #2
    Member Music Man's Avatar
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    Another way to find out what the inside of your chamber looks like is with cerro metal alloys.
    they can be bought at http://www.rotometals.com/Low-Meltin...lloys-s/21.htm
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

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    First off, there's no problem with how you are handling seating depth. There are multiple methods and tools to use to determine where the lands begin in your rifle. It would be helpful if you could use a chronograph to see what kind of velocity you are getting from the powder charge weights too.

    Once you determine the maximum (powder charge weight) safe velocity you want to use, you can test various bullet seating depths to find the sweet spot for your rifle in terms of accuracy. I usually test in .005 increments and shoot two three shot groups per seating depth. Once I find what I think is the optimum seating depth, I load six more rounds and shoot em to verify it.

    Since you are going to be shooting Partitions, I would recommend you use Nosler's recommended powder type(s) and charge weights. If you don't have Noslers reloading manual, their load data is available on line. Trying several different powders may also improve your results.

  4. #4
    Member jmg's Avatar
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    Quote Originally Posted by sep View Post
    First off, there's no problem with how you are handling seating depth. There are multiple methods and tools to use to determine where the lands begin in your rifle. It would be helpful if you could use a chronograph to see what kind of velocity you are getting from the powder charge weights too.

    Once you determine the maximum (powder charge weight) safe velocity you want to use, you can test various bullet seating depths to find the sweet spot for your rifle in terms of accuracy. I usually test in .005 increments and shoot two three shot groups per seating depth. Once I find what I think is the optimum seating depth, I load six more rounds and shoot em to verify it.

    Since you are going to be shooting Partitions, I would recommend you use Nosler's recommended powder type(s) and charge weights. If you don't have Noslers reloading manual, their load data is available on line. Trying several different powders may also improve your results.

    i have the Nosler loading book, and the rl19 is listed as the most accurate powder tested, and I am using their range amounts for amount to use. I do not have a chrono though, so I'll be skipping velocity tests for now.
    Never count your days, but rather, make all of your days count.

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