Distance to lands changes with different bullets

stello1001

stello1001

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    • Feb 20, 2017
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    Corpus Christi TX
    #1
    Hey all,

    I'll start by saying I'm months into reloading so still fairly new. However, I think I've done well overall. There is one particular rifle that has me confused and could use your help. I'm trying to reload for it and want to determine distance to lands so I know where that is and I don't start loading for it by jamming bullets. I generally back off 15 to 25 thou as a start. Details of rifle are below:

    Howa mini 1500
    6.5 grendel
    Virgin starline brass
    123 Amax
    123 SST

    I have stripped the bolt and confirmed that it falls freely both on itself and on a virgin piece of brass, as I am using. I've seated a 123sst little by little and place it on my bolt and send it in to battery to see where it free falls. Then I did the same with a 123Amax.

    123sst free falls right at 1.739
    123Amax free falls right at 1.7285

    Then I tried hornady factory ammo loaded with a 123BTHP. I was able to find two that measure right at 1.683 and one let's the bolt free fall and the other doesn't.

    I thought the factory ammo was probably because the cases are not consistent and some brass pieces are fatter than others. However, all my virgin starline has been good fitting and the problem is still present with those.

    I'm using hornady guages.
    Any tips?
     
    #3
    hafejd30 said:
    Get a hornady oal tool and modified case. Much more reliable than any other method I tried

    www.midwayusa.com

    Hornady Lock-N-Load Overall Length Ga Bolt Action

    The Hornady Lock-N-Load Overall Length Gauge is one of the best kept secrets to accurate reloading. This tool allows reloaders to quickly and easily...
    www.midwayusa.com www.midwayusa.com
    Click to expand...

    I've seen others be off by 1 to 3 thou after attempting multiple times to see if it was repeatable. Has your testing been more accurate than that?
     
    #4
    stello1001 said:
    I've seen others be off by 1 to 3 thou after attempting multiple times to see if it was repeatable. Has your testing been more accurate than that?
    Click to expand...
    I used to struggle with it due to inconsistent pressure I’d apply to the plastic stem than pushes on the bullet. Keeping the tool in the same spot each time and applying the same pressure each time on the back of the bullet has worked great for me

    You can apply enough pressure to kiss the lands or jam the bullet slightly into them if your not consistent

    I measure 3-5 bullets a few times each to make sure it’s consistent
     
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    #6
    Use the Hornady tool to get a decent starting point. It CAN be accurate but it does take some practice and a light touch.

    To eliminate your gorilla fist, there are other methods.
    I use a stripped bolt, a resized round without a primer, the bullet I want to use, a dry erase marker and an Ott Light.
    Use the Hornady tool. Strip the bolt. Seat the bullet to the Hornady tool length. Use the dry erase marker and write all over the bullet. VERY carefully load the bullet into the chamber (I like to clamp my rifle so that it is vertical, barrel up, no gravity to fight with), close the bolt and open the bolt carefully. Inspect the bullet for marks under the Ott Light. Remove all of the marker and seat a little deeper, mark up the bullet and repeat. You will be able to tell when there are no longer marks in the dry erase marker...I try to see marks in JUST the layer of ink but not on the copper jacket.
     
    #8
    Aftermath said:
    Use the Hornady tool to get a decent starting point. It CAN be accurate but it does take some practice and a light touch.

    To eliminate your gorilla fist, there are other methods.
    I use a stripped bolt, a resized round without a primer, the bullet I want to use, a dry erase marker and an Ott Light.
    Use the Hornady tool. Strip the bolt. Seat the bullet to the Hornady tool length. Use the dry erase marker and write all over the bullet. VERY carefully load the bullet into the chamber (I like to clamp my rifle so that it is vertical, barrel up, no gravity to fight with), close the bolt and open the bolt carefully. Inspect the bullet for marks under the Ott Light. Remove all of the marker and seat a little deeper, mark up the bullet and repeat. You will be able to tell when there are no longer marks in the dry erase marker...I try to see marks in JUST the layer of ink but not on the copper jacket.
    Click to expand...

    I'm not sure what you mean by Ott light. However, on one of the hornady factory ammo that did not allow the bolt to freely fall, I sharpie-ed it. After extracting, it looks like only one land is imprinting.

    I will try the dry erase marker next as I believe it might leave a thinner layer of ink. Also, the sharpie seems thick and sticky too.
     
    #10
    Baron23 said:
    Are you aware that you can erode the throat this much ^^ in just a 100 rounds. I can’t imagine .001-.003” being of any significance.

    Cheers.
    Click to expand...

    Yeah I suppose. Just stating why I use the method I use. If taking measurements, I want to take repeatable measurements.

    Still not opposed to the tool suggested when I made that reply and will probably end up buying it.
     
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    #11
    stello1001 said:
    Yeah I suppose. Just stating why I use the method I use. If taking measurements, I want to take repeatable measurements.

    Still not opposed to the tool suggested when I made that reply and will probably end up buying it.
    Click to expand...
    Index the bullet and comparator w/a sharpie so you're measuring at the exact same spot for that one bullet each time you do it. Otherwise you may see the variance you're describing...That said .001-.003 doesnt even begin to move the needle in terms of impact on target/mean error radius, general precision unless you're running VLD bullets damn near at the lands.
     
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    #12
    stello1001 said:
    I'm not sure what you mean by Ott light. However, on one of the hornady factory ammo that did not allow the bolt to freely fall, I sharpie-ed it. After extracting, it looks like only one land is imprinting.

    I will try the dry erase marker next as I believe it might leave a thinner layer of ink. Also, the sharpie seems thick and sticky too.
    Click to expand...
    We have 2. Both are bright lights (lamps) that include a large magnifier lens that allow for a detailed view, even if your eyes are old, of the gorilla fisting you just did to your Hornady tool.


    EDIT: I want to add that I don't use the Hornady tool until I am at the point of not seeing marks in the ink. I don't care what it's jammed as that is not what I am after. I clean the marker off, seat it deeper, mark it up and check...no measuring.

    I do go ahead and measure once I find that point where the bullet is not actually on the lands. Then, after I do seating depth tests, I measure again. I write the CBTO measurement on the case with permanent marker as my reference or benchmark, noting the distance from the lands as a minus number...for example: BTO: 2.92"; -0.012"
     
    Last edited:
    #15
    stello1001 said:
    This was my thought but didn't want to bias others by including it in my OP lol.
    Click to expand...

    IMHO once we start talking about a half of a thou, it's arguable that we're inside the tolerance of what calipers and comparators can tell us LOL. It could just be dust or oil on one of the bullets that'd otherwise mic out the same as the other, maybe wipe them off real good with IPA and measure again? 😝
     
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    #16
    stello1001 said:
    This was my thought but didn't want to bias others by including it in my OP lol.
    Click to expand...
    Yes, different bullets from different manufacturers will have different length bearing surfaces and ogive shapes. I take measurements with different bullets I use before load development just to see where the lands is relative to that bullet.

    I also track throat erosion and to do that I've set aside a single bullet that I save and use every time to measure where the lands is. I don't do this to change my seating depth (like for chasing the lands), but simply to monitor throat erosion. Using the same bullet for this task takes the variations that different bullets have out of the equation.
     
    Last edited:
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