Measuring Distance Into the Lands

just_jon

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I was reading somewhere this weekend about seating bullets X thousands into the lands. The discussion referenced a seating depth test with bullets seated both into the lands and touching the lands. COAL for bullets seated into the lands was longer than those touching the lands. Hoping someone here can help me understand how this distance beyond the lands is measured.
 

MagnumManiac

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First you find ‘touch’, which can be done as simply as slitting a case neck with a Dremel, clean up the burrs and place a bullet in the neck and chamber it. This will give you your touch measurement because there will not be enough tension to force the bullet into the rifling.
Once this is determined, you then seat your bullet .xxx” amount of jam you want longer than that first measurement.

Cheers.
 

just_jon

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That is sort of what I was envisioning, but wouldn’t you need some serious neck tension to prevent the bullet from pushing back into the case?
 

Csafisher

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Are f class and top bench rest guys jamming their bullets? I could be wrong but I don’t think so. At least not the vast majority of them. That measurement will change as you shoot more as well...
 

QuietTexan

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Unpopular answer:

There's no such thing as seating "into the lands", there's only seating "further than wherever the person measuring decided to stop to pushing" based on what they're using for tension/interference fit or how they're measuring. There's a big presumption about concentricity implicit to measuring this relationship - if anything isn't concentric, including the end of each separate land of rifling, the bullet jacket, and the neck of the bullet, then the actual interface point will change every shot. Over the life of a bore who really thinks a throat erodes perfectly concentrically?

So either 1 - jam the bullet in hard until all the variables are reduced to the most difficult to overcome (aka would seat a bullet back into the neck against interference fit), or 2 - jump the bullet and don't worry about trying to get an absolute measurement to the lands, use the initial measurements to create a reference point that in and of itself means nothing while focusing on what works the best for your goal, be that absolute precision or a longer useful life of a seating depth.
 
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buggz

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Shrug, it's all 'relative' measurement any way?
What is jam tight and slight touch is not the same meaning to everyone.
I guess, consistency is what is really sought after.

I got 'blasted' for posting the following on another forum,
as the first method compared to the last two,
had a huge difference in measurement.

 

MagnumManiac

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Are f class and top bench rest guys jamming their bullets? I could be wrong but I don’t think so. At least not the vast majority of them. That measurement will change as you shoot more as well...
I shoot F-class open, I test at touch, but do not jam….
David Tubb jams EVERYTHING he has ever shot.
What does that tell you.
The OP didn’t ask the reasons why, only how it was done.

Cheers.
 

FEENIX

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I was reading somewhere this weekend about seating bullets X thousands into the lands. The discussion referenced a seating depth test with bullets seated both into the lands and touching the lands. COAL for bullets seated into the lands was longer than those touching the lands. Hoping someone here can help me understand how this distance beyond the lands is measured.

 

wildbillb02

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Just remember if it's jammed it will probably stay if you eject the round. Powered everywhere and the bullet still in the lands
 

justinp61

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First you find ‘touch’, which can be done as simply as slitting a case neck with a Dremel, clean up the burrs and place a bullet in the neck and chamber it. This will give you your touch measurement because there will not be enough tension to force the bullet into the rifling.
Once this is determined, you then seat your bullet .xxx” amount of jam you want longer than that first measurement.

Cheers.
I only load for hunting rifles but this is the method I use. I'll do it five times and it usually comes out to within a couple thousandths. Anything way out of the average I throw out and measure again. I had one of the Hornady tools and couldn't get consistent measurements.
 

misterc01

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Interesting "thought exercise" - First question the question brings to mind is "what is the purspose of the exercise?" General knowledge is always a good thing. How you proceed with that knowledge is the real question. Like many, if not most, on the forum - it is the optimization of your accuracy that is the goal. And how far the bullet is relative to the lands is the goal of seating depth that give sthe shooter the best results. Once all the properties of the rifle/bullet/powder/primer/case, etc are where the shooter wants them to be, then rest of the equation is the ability of the shooter. I have my process, and MR Cortina offers excellent advcie as well.
 
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