Bullet Seating Depth

[GLTaylor]

Mikecr is absolutely correct.
Find a wide node of seating depth that your barrel likes and shoot. Let the target tell you if it's time to recheck your seating depth.
Extensive testing was done on the Precision Shooting forum and also tests by Eric Cortina. Good reading!

 

[QuietTexan]

To be fair didn't say he was chasing the lands, just tracking the wear. It is an interesting data point over the lift of a barrel, especially one that erodes quickly or you shoot a lot of volume through. One way to not disprove the "deep node" concept (that I agree with) that doesn't move over the life of the barrel is by tracking throat wear against group size, and not showing correlation.

 

[Mikecr]

Throat erosion and accurate barrel life may loosely seem to correlate, but they're mostly unrelated.

What ultimately kills accuracy from a bore is carbon constrictions (not erosion).
The heat impinges carbon into the bore surface, raising it -in some places. In other places this does not occur, but where the bullet was already swaged/damaged, it no longer fits right beyond.

Grouping opens from this, and for the folks who actually reach and demonstrate peak precision from bores, they see the change occur like a flipped switch. Many point blank BR shooters J-B lap between matches, or even relays, to manage this. Their accurate barrel life is not long (~900rnds), and they don't hesitate to spin another barrel on when they see the flashing sign. That is, when J-B treatment no longer recovers performance.
I've noticed occasions when a barrel shot so well(a hummer) that a shooter just didn't want to let it go. They would have it set back, and get another 200rnds of peak performance. But that was all they got,, it was dubious,, and hardly worth it. What they briefly recovered there was high starting pressure, not accurate barrel life.

 

[cape cove]

Throat erosion and accurate barrel life may loosely seem to correlate, but they're mostly unrelated.

What ultimately kills accuracy from a bore is carbon constrictions (not erosion).
The heat impinges carbon into the bore surface, raising it -in some places. In other places this does not occur, but where the bullet was already swaged/damaged, it no longer fits right beyond.

Grouping opens from this, and for the folks who actually reach and demonstrate peak precision from bores, they see the change occur like a flipped switch. Many point blank BR shooters J-B lap between matches, or even relays, to manage this. Their accurate barrel life is not long (~900rnds), and they don't hesitate to spin another barrel on when they see the flashing sign. That is, when J-B treatment no longer recovers performance.
I've noticed occasions when a barrel shot so well(a hummer) that a shooter just didn't want to let it go. They would have it set back, and get another 200rnds of peak performance. But that was all they got,, it was dubious,, and hardly worth it. What they briefly recovered there was high starting pressure, not accurate barrel life.

Great info. TKS

 

[Tac-O]

Throat erosion and accurate barrel life may loosely seem to correlate, but they're mostly unrelated.

What ultimately kills accuracy from a bore is carbon constrictions (not erosion).
The heat impinges carbon into the bore surface, raising it -in some places. In other places this does not occur, but where the bullet was already swaged/damaged, it no longer fits right beyond.

Grouping opens from this, and for the folks who actually reach and demonstrate peak precision from bores, they see the change occur like a flipped switch. Many point blank BR shooters J-B lap between matches, or even relays, to manage this. Their accurate barrel life is not long (~900rnds), and they don't hesitate to spin another barrel on when they see the flashing sign. That is, when J-B treatment no longer recovers performance.
I've noticed occasions when a barrel shot so well(a hummer) that a shooter just didn't want to let it go. They would have it set back, and get another 200rnds of peak performance. But that was all they got,, it was dubious,, and hardly worth it. What they briefly recovered there was high starting pressure, not accurate barrel life.

At the end of a barrel's life, is that carbon just not removable? Is it chemically or physically embedded into the steel somehow?

 

[QuietTexan]

Throat erosion and accurate barrel life may loosely seem to correlate, but they're mostly unrelated.

That's why I said there isn't a correlation between throat erosion and group size. Other factors are the driving force behind barrels being shot out, and a deep seating node should last for the life of a barrel.

I'm trying to agree with you. Let me agree with you.

 

[Stan Malinky]

Good discussion I have learned more about carbon constrictions than ever before.

Since we are talking about carbon where is the location of the carbon ring and how can it be stopped from forming? Once formed best way to remove it?

 

[Black Hat]

As Mikecr is alluding to, the actual number does not matter even if not repeatable. Pick one of those numbers and do seating depths from there.

This is what I do, I run the measurement 10 times and use the average, all your looking for is a baseline to start from.

 

[OldDutch]

Throat erosion and accurate barrel life may loosely seem to correlate, but they're mostly unrelated.

What ultimately kills accuracy from a bore is carbon constrictions (not erosion).
The heat impinges carbon into the bore surface, raising it -in some places. In other places this does not occur, but where the bullet was already swaged/damaged, it no longer fits right beyond.

Grouping opens from this, and for the folks who actually reach and demonstrate peak precision from bores, they see the change occur like a flipped switch. Many point blank BR shooters J-B lap between matches, or even relays, to manage this. Their accurate barrel life is not long (~900rnds), and they don't hesitate to spin another barrel on when they see the flashing sign. That is, when J-B treatment no longer recovers performance.
I've noticed occasions when a barrel shot so well(a hummer) that a shooter just didn't want to let it go. They would have it set back, and get another 200rnds of peak performance. But that was all they got,, it was dubious,, and hardly worth it. What they briefly recovered there was high starting pressure, not accurate barrel life.

I had never heard this. Super interesting. Is there a way to see this or test this in a barrel?
It seems like a lot of barrel accuracy issues could be mistakenly attributed to that if not.

 

[Mikecr]

There is a destructive way that I've seen. Shoot about 500rnds of moly coated bullets without serious cleanings and you will see accuracy step change worse. You'll also notice a carbon ring about midway down the barrel. In this case it's a moly ring causing constriction that you can feel with a patch.
The problem at this point is that you can't get rid of that ring without permanently damaging the bore..
So you have in effect ended accurate barrel life right there.

Yeah the barrel might still be accurate enough, but it's 'potential' is forever gone.
Folks, don't let your kids play with moly..