SEATING DEPTH - question

[hemiford]

When you are adjusting seating depth, do very small adjustments seem more critical
the closer you are to touching the rifling ?

In other words, if you are .200 off the lands, will you see differences in precision with .003" seating depth changes
in the same way that .003" changes will give you differences in precision when you are very very close to jammed ?

The farther away from jammed, the less dramatic the observable change ?

 

[Eric H]

Haven't experienced that since once I see promise in a load, I adjust .005 increments.

 

[AZShooter]

I always thought that minor seating depth changes might not show much difference with a chamber like the Weatherby lineup. They use a freebore of .375" in some of their chamberings.

 

[Phil Rizzo]

When you are adjusting seating depth, do very small adjustments seem more critical
the closer you are to touching the rifling ?

In other words, if you are .200 off the lands, will you see differences in precision with .003" seating depth changes
in the same way that .003" changes will give you differences in precision when you are very very close to jammed ?

The farther away from jammed, the less dramatic the observable change ?

There is only one good way to find out. And it won't take long, especially if you know the powder/charge weight/primer/bullet are good in your rig.

 

[Phil Rizzo]

Haven't experienced that since once I see promise in a load, I adjust .005 increments.

I remember when I thought there was no way less than .005 increments could matter.
Now the BR guys are at .001!

 

[memtb]

It stands to reason, at least in my feeble mind, that the closer you are to the lands….. the more important small adjusts are.

I would think that if the actual fractional adjustment is the same throughout the adjusting range …….the percentage of adjustment is greater as the value of "jump" is decreased!

Wow, that gave me a headache to arrive with that theory…..I need a nap now! memtb

 

[Mikecr]

Jam, touching, or only a few thou off the lands (OTL) adds [starting pressure] to seating testing.
This greatly affects barrel timing and tune.

When you find optimum seating >5thou OTL, then you're way less affecting, or relying on, that bullet sourced starting pressure.
So you won't have to chase lands with that bullet/setup to keep a tune.

The optimum seating window width is otherwise independent of land distance, and more about the bullet nose/freebore/throat.
For instance, whether you find optimum seating around 10, or 20thou off, or 80thou off,, it's as likely that your window there is ~5-10thou wide.
But, the window could be narrower or wider.

 

[imyourhuckleberry]

In other words, if you are .200 off the lands, will you see differences in precision with .003" seating depth changes
in the same way that .003" changes will give you differences in precision when you are very very close to jammed ?

You may see stringing if the same loads you are shooting have different seating depths.

 

[marchboom]

It stands to reason, at least in my feeble mind, that the closer you are to the lands….. the more important small adjusts are.

I would think that if the actual fractional adjustment is the same throughout the adjusting range …….the percentage of adjustment is greater as the value of "jump" is decreased!

Wow, that gave me a headache to arrive with that theory…..I need a nap now! memtb

This ^^^^^

 

[Lenny Foffa]

For me seating depth changes come at or near the end of the load development process! Ok so I know the brass I will use and the weight of that brass; next I know the bullet and the weight of that bullet I want to use ; I know the primer I will use. And then the powder and the weight of the charge . ( or pretty close to it ) ! I've got some really good three shot groups , so now let's see what .005 closer to the lands gets me , and let's see what .005 further off the lands gets me ! I also must always remind myself , if the condition's are different, the test may be a waist of time ! Then I must repeat it !

 

[Mikecr]

Minor seating tweaking (like +/- 5thou) is not full seating testing.
It's fiddling with barrel timing/tune.

Full seating testing is not tuning.

 

[MagnumManiac]

Well, I've been testing seating depth first for a very long time and have discovered that once it is found, powder testing shows exactly what the rifle likes in powder choice. Even without a tuner, my rifles will exhibit a point where even wide changes of +/- .010" seating depth has minimal effect on target, yet the powder charge may show wide discrepancies with just a .2g variance. This tells me the powder isn't stable at that amount, so start pressure is fluctuating, which is always proved over the pressure trace.
I can't test new barrels anymore, because I have no more new strain gauges to fit on new barrels.
I never try to tune a load with seating depth because it changes start pressure, which takes your powder node out of optimum…

Cheers.

 

[Hawk in WY]

Another possibility is testing the seating depth is fine-tuning case capacity, which affects pressure.

If that's the case, the distance from the lands will have nothing to do with it.

 

[MagnumManiac]

Another possibility is testing the seating depth is fine-tuning case capacity, which affects pressure.

It has not been proven that changing case capacity via seating depth is changing the pressure outcome, what is proven is that it changes start pressure and therefore barrel time of bullet travel, therefore changing barrel whip condition at exit.

Cheers.