Help! Distance to the lands

[Jud96]

The Wheeler method is the best way I have found. I've used the Hornady and Sinclair tool and used some similar to the Frankford Arsenal tool and the sharpie method. None of them give me the repeatability or the confidence like the Wheeler method does. You also don't need any gadgets or special items to use the Wheeler method.

 

[The Oregonian]

The exact measurement is not that important. It is just a place to start.

That is true, but if you have to chase the lands at all as the throat wears I don't know how you could reliably chase it trout knowing distance from the lands. Maybe I am missing something though.

 

[LongBomber]

Other than not sticking a bullet in the barrel, why bother with finding the lands at all? The lands are not a long term fixed point, they are a measurement that changes with use. And as long as you are not sticking bullets in the barrel when you extract a round who cares?
You need to run a seating depth test to find the correct seating depth range for your specific bullet/barrel combo. The relationship to the lands is immaterial.

 

[LongBomber]

That is true, but if you have to chase the lands at all as the throat wears I don't know how you could reliably chase it trout knowing distance from the lands. Maybe I am missing something though.

There was some good reading over on the PRB blog page on seating depth. I did a bit of testing with a couple of my rifles, once out at .060-0.080" the seating depth window became much larger. And I am not sure that you really need to change the lands, or maybe not in all cases. My last 6.5-284 went 1400 rounds and I never moved the seating depth, it stayed competative the entire time so I didnt fool with it.

 

[The Oregonian]

There was some good reading over on the PRB blog page on seating depth. I did a bit of testing with a couple of my rifles, once out at .060-0.080" the seating depth window became much larger. And I am not sure that you really need to change the lands, or maybe not in all cases. My last 6.5-284 went 1400 rounds and I never moved the seating depth, it stayed competative the entire time so I didnt fool with it.

I'm sure it is cartridge by cartridge as well. Only one I have had to move was a 28N, which is about the be rebarreled to a 30N to shoot the 215's.

 

[Jud96]

I agree with not chasing the lands. I shoot until something changes. Don't change anything until it's broke.

 

[Mikecr]

That is true, but if you have to chase the lands at all as the throat wears I don't know how you could reliably chase it trout knowing distance from the lands. Maybe I am missing something though.

You only need to chase lands if you develop a load with an in that lands(ITL) relationship.
If you develop and accept something off the lands(OTL), you will never need to change CBTO (from initial best) for the accurate life of that barrel.

Given this, unless shooting an underbore that requires extreme starting pressures to perform, don't even bother with ITL development. It ain't worth it.

 

[The Oregonian]

You only need to chase lands if you develop a load with an in that lands(ITL) relationship.
If you develop and accept something off the lands(OTL), you will never need to change CBTO (from initial best) for the accurate life of that barrel.

Given this, unless shooting an underbore that requires extreme starting pressures to perform, don't even bother with ITL development. It ain't worth it.

Interesting...I would think if you are .020" OTL and the lands erode that you would need to seat slightly longer over time.

What is the rationale for not needing to change the seating depth as the throat is worn? Thanks.

 

[QuietTexan]

You work to find a range that is wide enough to not require adjustment as frequently as the throat wears. PRB did a series on it that addresses throat erosion in PRC over longer strings of fire which would require the adjustment of seating depth during a normal match. They will see throat erosion during one match greater than a commonly promulgated seating depth adjustment of 0.005". Here's the main thrust of it:

What if instead of looking for the one exact bullet jump that provides 100% optimal precision and having to constantly adjust the seating depth as the lands of the barrel erodes, we instead looked for the bullet jump that is very forgiving AND still provided good precision over a wider range of jumps?

Bullet Jump Research: Executive Summary & Load Development Tips

This is the last post in a series of articles focused on bullet jump research that has been conduct...

precisionrifleblog.com

 

[Mikecr]

For one, seating depth adjustment is not normally about 'tune'. There are enough ways other than seating to get tune.
-We're simply finding the optimum bullet-bore interface.
-Others, competing with underbores, need prerequisite seating for particular(usually very high) starting pressures.
Be careful to understand that these are different situations.

With a new barrel & bullet you have a relatively abrupt bullet-bore interface.
Picture a ping-pong ball held just outside a tight fitting lotto tube, and released to suck into it.
At certain distances it rattles around on entry, and at other distances it jets right in cleanly.
Back to seating, we find an optimal distance where the bullet enters bore consistent and cleanly.
This is normally off the lands(OTL), and from there the leade wears with THAT bullet.
Keep the same bullet at initially tested best CBTO, and it will not need seating adjustment again for the accurate life of that barrel.
Change bullets, and regardless of wear, you will likely need to change seated CBTO for a new optimal.

With bullets ITL, or otherwise set with a land relationship specifically to affect tune, well that's a pretty precarious condition given constant change. For those folks on this path, they gotta do what they gotta do..
This is NOT what should be done with a hunting capacity cartridge, as any gain in it (doubtful) would be fleeting.

I hope this makes sense.
To summarize; people who need to chase lands to hold their tune have put themselves in that position.
The rest of us have not.
So why would anyone seat so close to lands that it hugely affects tune, and then rely on that?
Well, if you're competing with a tiny little underbore (like a 6PPC), you are rewarded for pressure peaks that are beyond viable (or safe) for hunting capacity cartridges. These peaks are well into diminished returns, which also equals diminished variance of returns. They don't even need to measure their powder beyond clicks dialed into throwers, because variances there are normalized inside 75-80kpsi peaks.
And to get these peaks requires high starting pressures provided by fast powder, FL sized necks(extreme tension) and ITL seating.
Now they tweak seating inside this same land relationship -for group shaping. But, that is not tuning. It's still optimizing communication with the bore, just as we do(over a far larger span).

Another case where people end up chasing lands is when they engaged in a poor load development process.
They pulled some seated CBTO out of their butts for powder development, and THEN went to seating testing from their powder node. As they adjusted seating and shot groups, they hit on a setting(randomly) that really tightened groups, and they jump all over that. They rely on it. BAD MOVE.
They included a seating that may or may not be optimal -for tune.
THis is how so many people think that seating is tuning.
It is not.
Seating affects tune, but is not tune.
The opposite also occurs where they pull seating out of their butts for powder testing, then test seating, and find that ANY seating from their guess shoots worst groups. So then it's assumed that their guessed seating was best. Wrong.
They just never get that seating is different and needs to be seen independently of powder, and then added to powder.

 

[Plinker147]

I think a simple way of stating it is what the distance to the lands is doesn't matter. The measurement that matters is the CBTO that shoots good in your gun. Once that is established your good. If your lands erodes over the time and you load doesn't shoot as well, there is no need to remeasure the distance to the lands. All you need to do is adjust CBTO until your load shoots like it did originally. Doesn't matter if ends up .100 off or .020 off just as long as the accuracy is there.

For the OP question it is not uncommon to get different measurements with different methods. We are still talking small differences. I use Sinclair's and I will get a few different measurements. Just do it multiple times and take the average.

You must initially find the lands measurement to know that your starting off the lands. That does matter for a hunting rifle as it's never good to stick a bullet in the field.

Sounds like your doing good

 

[The Oregonian]

For one, seating depth adjustment is not normally about 'tune'. There are enough ways other than seating to get tune.
-We're simply finding the optimum bullet-bore interface.
-Others, competing with underbores, need prerequisite seating for particular(usually very high) starting pressures.
Be careful to understand that these are different situations.

With a new barrel & bullet you have a relatively abrupt bullet-bore interface.
Picture a ping-pong ball held just outside a tight fitting lotto tube, and released to suck into it.
At certain distances it rattles around on entry, and at other distances it jets right in cleanly.
Back to seating, we find an optimal distance where the bullet enters bore consistent and cleanly.
This is normally off the lands(OTL), and from there the leade wears with THAT bullet.
Keep the same bullet at initially tested best CBTO, and it will not need seating adjustment again for the accurate life of that barrel.
Change bullets, and regardless of wear, you will likely need to change seated CBTO for a new optimal.

With bullets ITL, or otherwise set with a land relationship specifically to affect tune, well that's a pretty precarious condition given constant change. For those folks on this path, they gotta do what they gotta do..
This is NOT what should be done with a hunting capacity cartridge, as any gain in it (doubtful) would be fleeting.

I hope this makes sense.
To summarize; people who need to chase lands to hold their tune have put themselves in that position.
The rest of us have not.
So why would anyone seat so close to lands that it hugely affects tune, and then rely on that?
Well, if you're competing with a tiny little underbore (like a 6PPC), you are rewarded for pressure peaks that are beyond viable (or safe) for hunting capacity cartridges. These peaks are well into diminished returns, which also equals diminished variance of returns. They don't even need to measure their powder beyond clicks dialed into throwers, because variances there are normalized inside 75-80kpsi peaks.
And to get these peaks requires high starting pressures provided by fast powder, FL sized necks(extreme tension) and ITL seating.
Now they tweak seating inside this same land relationship -for group shaping. But, that is not tuning. It's still optimizing communication with the bore, just as we do(over a far larger span).

Another case where people end up chasing lands is when they engaged in a poor load development process.
They pulled some seated CBTO out of their butts for powder development, and THEN went to seating testing from their powder node. As they adjusted seating and shot groups, they hit on a setting(randomly) that really tightened groups, and they jump all over that. They rely on it. BAD MOVE.
They included a seating that may or may not be optimal -for tune.
THis is how so many people think that seating is tuning.
It is not.
Seating affects tune, but is not tune.
The opposite also occurs where they pull seating out of their butts for powder testing, then test seating, and find that ANY seating from their guess shoots worst groups. So then it's assumed that their guessed seating was best. Wrong.
They just never get that seating is different and needs to be seen independently of powder, and then added to powder.

Thanks...so are you saying to do seating depth first with a safe charge to find the optimal depth, and then use that consistently for powder charge testing?

 

[Kmccord]

When I called Berger and talked to one of there techs, he mentioned, do a seating test first with the minimum powder charge for the bullet you are using. Once you find a seating depth that performs consistently, then work on your powder charge. I did this with the Grandson 7mm Rem Mag and it worked perfectly. In the past I did this backwards, at .020 off the Lands looking for the best powder node before changing seating depth. What I found out using seating depth test first, I found several powder charges that would perform .5 or less once I started testing for powder charges, I ended up taking the one with the best ES and SD out of three that performed great.

 

[Mikecr]

You got it.
Full seating testing first. This is a coarse prerequisite for beginning CBTO.
Then Powder testing, OCW or ILD/Ladder.
Then fine seating tweaking in it's window. This is for tightest group shaping only, and will not collapse your powder load while OTL.
Log your final CBTO, and never change it for that bullet and that barrel.
Down the road, when your grouping takes a step change, that's the end of your accurate barrel life.
Don't chase your tail at this point with a bunch of changes. Instead have a plan to replace the barrel (saves time & money).

Given this process order, you can do full seating testing, and primer swapping (another non-tune prereq) during fire forming of new cases. Never move into powder until cases are fully fire formed and stable with your sizing plan.
Else you'll be chasing your tail right out of the gates.

Add: Barrel life and accurate barrel life are different and independent.
Barrel life is a duration of continued function, and meeting expectations little beyond that (like still 1moa).
Accurate barrel life is a duration of peak results. You first need to find a barrel's potential before you can see it leave.