Seating depth explained for the newbies

jasonco

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With all the new shooters, all of a sudden and those getting started in handloading, this should clear up seating depth problems, you might have or not be aware of. I figured this out long ago when I bought a factory Rem LR 300 RUM, with it's long throat and standard magazine length, which is the jam length, and I was only able to go away from the lands, to remain mag fed, to find the rifle's optimum seating depth node.

EC explains this better on a video than I could on paper, without writing a chapter on it! I just recalled this from when he put it up, as I'm just now getting around to starting load development on another 28 Nosler barrel and thought other's might find it handy.

I have never chased the lands. Wore out a 7STW barrel and never adjusted seating depth, once I found the node and it still grouped with a throat that would make a Weatherby fan boi green with envy. Only reason it got replaced it was, I couldn't make new 7STW brass for it (300 WB necked to 7mm).

This ain't F-Class, but you can learn a lot from it!



 

Laguna Freak

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Erik illustrates a good method for sure. I don’t follow it exactly as he outlines though because I want to find nodes that are further from the lands than he illustrates here. I do this because I believe longer jumps reduce throat erosion and/or the effects of throat erosion on accuracy, per Precision Rifle Blog documentation. If I recall correctly, Erik disagrees with this assertion but to each his own.
 

jasonco

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Erik illustrates a good method for sure. I don’t follow it exactly as he outlines though because I want to find nodes that are further from the lands than he illustrates here. I do this because I believe longer jumps reduce throat erosion and/or the effects of throat erosion on accuracy, per Precision Rifle Blog documentation. If I recall correctly, Erik disagrees with this assertion but to each his own.
I've read that too but, how can shortening cbto, extend throat life, when cartridge length is the same more or less? And as to cartridge length, I use Sinclair Cartridge Length Ganges to see exactly, what the chamber length is, not a SAAMI value.
 

Laguna Freak

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I've read that too but, how can shortening cbto, extend throat life, when cartridge length is the same more or less?
This is a very good question that I would be surprised if anyone could answer definitively. I don’t understand the metallurgy and explosive erosion well enough to offer an informed opinion. Those that claim to have tracked erosion through competition say it is true. Eg; Precision Rifle Blog contributors.

That’s good enough for me since I get better accuracy with longer jumps on two different rifles and I have not been chasing lands since I started applying this method last year.
 

jasonco

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This is a very good question that I would be surprised if anyone could answer definitively. I don’t understand the metallurgy and explosive erosion well enough to offer an informed opinion. Those that claim to have tracked erosion through competition say it is true. Eg; Precision Rifle Blog contributors.

That’s good enough for me since I get better accuracy with longer jumps on two different rifles and I have not been chasing lands since I started applying this method last year.
Barrels erode when you use them. Want zero erosion, practice zero use?

When scope barrels, there's erosion but, useful hunting accuracy stays for a long time. This long range hunting game, not 200+ rounds weekend competition. I have several comp rifles and I know that acceptable barrel accuracy is finite and expect to re-barrel at some point. Barrels, like ammunition are expendable.
 

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