Hope this thread doesn't turn into a pissing match. I've found discussions on this subject can get quite "spirited". Especially when the subject of headspacing belted magnums on the shoulder is discussed. But please don't avoid that subject because headspacing belted cartridges off the shoulder is a subject I'm particularly interested in.

I'm mainly interested in what works for you and what caliber your method is successful for.

There actually are some differences in opinion and experience on this subject. For a long time I personally was of the opinion that simply neck sizing a cartridge that is "fireformed" to the rifle I'm loading for consistently yielded the ideal headspace. I've heard some pretty convincing arguments that although that method matches the chamber the best it may not be the optimum headspace for that cartridge in that weapon.

With that last statement I guess this can of worms is now open.

Optimal accuracy is achieved by positioning the ogive of the bullet off the lands. This entails understanding how the throat of your chamber/barrel is configured.

Here's a good discussion of headspacing, chambering, factory chambers, "tight" custom chambers, fireforming, etc.

http://www.varmintal.com/arelo.htm

Varmint Al is a retired structural engineer, Lawrence/Livermore Labs -- "The Atom Bomb People."