I use the dimension of .050 - .035 left unengraved by the throat or lands. I throat all my guns with a free bore of .001 larger than groove size so, it's harder to see where it starts. This I learned from Ron Long in my first months of shooting back in '85. It's always worked out. I've set many rifles up for breach seating and it's never failed in that range. Like Boats says, if it's in to far, it won't shoot. 

The BSer on my very first target gun wasn't adjusted and I shot many rounds before I found out what was wrong (in to far).

You also need a bullet that's at least .001 larger than the throat. It's thoughts two things that seal the bore when the powder gasses hit it.

I've never tried seating out beyond .050 but, that would be better than in to far. I think you could get away with (maybe not as accurate) with any depth that has the last grease groove inside the barrel.

Frank

I looked up my seating depth in my range notes and I’ve got; “set the breechseater so that .050 is left uncut by the lands.”

I never measured any of mine. When they shoot the most accurate I leave it there. Wherever there is. Wouldnt even know how or from where to measure it. It's way to technical for me.   

             Joe. 

With a tapered bullet; I push them forward enough to get the wider base band to seal. It generally works out that half the base band is engraved. I then balance my powder load for the depth I have chosen to seat the bullet at as opposed to those who instead try to find their sweet spot by adjusting their seating depth.

My arguement is the bullet has to be ideally placed to have the best and most immediate gas seal on the base of the bullet to prevent gas cutting or variations in gas pressure.

There is always a barrel sweet spot within  .3 grains of powder. Load three loads of one tenth grain of powder and then find the sweet spot for where you have chosen to set your bullet.

For me this approach for finding the sweet spot has worked on any manufacturer of the barrel, with black powder or smokeless;  and for a diversity of bottleneck cases.

But then there are also one sweet spot for your barrel  that is better than the other sweet spots. Sorry I don' tell everyone how to find the best sweet spot.

J louis, I think the more accurate measurement is from the face of the locking lug on the breechseater to the end of the extended plunger. The cartridge case itself has little to do with the measurement, unless you are using a plugged case to breechseat th bullet.   ledball

I might be missing something but seems to me the thing that's important is how the bullet fits. How far in front of the case is irrelevant as is how deep the bullet is, smaller ones with more taper will  seat further in the lands fatter blunter shape ones not so far. Whatever the bullet correct engagement and good seal is the objective

Distance the bullet sits in front of the case sets the size of the combustion chamber. It might be one size it might be another, it's still a chamber that a certain amount of powder is going to have to ignite in and get up to burn rate. If the distance in front of the case is more one rifle than another it just takes more powder. 

I just can't see any reason to measure it or use measurements to come to any conclusions. Too many other variables are more important. If there is a perfect distance, one that's more important than bullet fit or correct powder charge have another go at explaining to me.

It is useful to record what works well in individual rifles and a gauge case brass rod filled does that very well.

Boats

Plus one to Frnkeore.  Mine measures at .042
Regards, Joe