Distance to lands changes with different bullets

[stello1001]

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?

 

[hafejd30]

Get a hornady oal tool and modified case. Much more reliable than any other method I tried

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...

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[stello1001]

Get a hornady oal tool and modified case. Much more reliable than any other method I tried

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

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?

 

[hafejd30]

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?

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

 

[CK1.0]

Just make a dummy round and use the Deep Creek Method:

 

[Aftermath]

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.

 

[stello1001]

Just make a dummy round and use the Deep Creek Method:

This is my method

 

[stello1001]

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.

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.

 

[Baron23]

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?

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.

 

[stello1001]

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.

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.

 

[nn8734]

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.

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.

 

[Aftermath]

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.

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.

https://ottlite.com/products/2-in-1-led-magnifier-floor-and-table-light

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"

 

[CK1.0]

Due to the differences in each bullet's ogive, your comparator might measure at a different spot than where your rifling actually engages the different bullets (at least that'd be my guess).

 

[stello1001]

Due to the differences in each bullet's ogive, your comparator might measure at a different spot than where your rifling actually engages the different bullets (at least that'd be my guess).

This was my thought but didn't want to bias others by including it in my OP lol.

 

[CK1.0]

This was my thought but didn't want to bias others by including it in my OP lol.

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?

 

[straightshooter1]

This was my thought but didn't want to bias others by including it in my OP lol.

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.