Seating depth

[wboggs]

What is the optimal seating depth without consideration of overall length? Base of bullet at shoulder neck junction, boatail bearing surface junction at shoulder neck junction, Some variation of these two choices?
The rifle can have any length throat to accommodate long OAL loads. What is the effect of seating depth on donut formation?
Thanks
Bill

 

[barefooter56]

wboggs,
The optimal seating depth is the distance from the lands or into the lands where the rifle is most accurate. The measurement is based on the Cartridge base to ogive (CBTO) . The effect of bullet seating depth v the "donut" comes into play when the "donut" comes in contact with the bullet causing excessive grip or neck tension on the bullet increasing pressure.

 

[wboggs]

Phil Thanks for your input. Understand your point about seating to a base to ogive for optimal accuracy. I would think this depends on the throat. Assume you can vary the throat and overall length to keep a constant bearing surface to rifling measurement ( jump or jam) what is the optimal position of the bullet in the case?
Also, what causes donut formation in an unaltered case?
Lastly, thanks for all the technical information Berger provides.
Bill

 

[hogan]

Bullet to neck shoulder junction if plain/spitzer base.
Boattail can sit below; thus avoiding donut horrors.

 

[fguffey]

What is the effect of seating depth on donut formation?

I have chambers that will never cause a do-nut. I have chamber I form cases for, on those chambers I create do-nuts in the case before the case is fired.

F. Guffey

 

[barefooter56]

wboggs,
You can "chase" the throat by setting the bullet out to maintain your bullet seating depth accuracy node as the throat erodes to a certain point. That point depends on how much of the bullet is left in the case neck. Hunting needs about 2 calibers. Target at least one to be safe. The dreaded doughnut is usually caused by hot loads weather you are neck turning or not. If the bullet is not seated deep enough in the case neck so the doughnut does not contact the bullet when its seated its usually not an issue. Its when it does contact the bullet causing excessive neck tension that it creates pressure issues. The doughnut can be removed usually by using an expander mandrel of the proper caliber and expander die and push the doughnut back out by running the expander mandrel down through the neck before neck sizing or by using a neck reamer that is same size or .001 under the bullet diameter on the unsized case neck to remove it. This usually involves a custom reamer. L.E Wilson is a good source for these.