Please don't laugh too hard, I have a question about neck turning that is probable quite simple but I am haveing a hard time visualizing. SOme one har written about turning on a mandril before turning the neck. It makes some since to me that you need the differences in the neck thickness to be on the outside and not on the inside. I am having a hard time picturing this, If you turn the outside how does that change where the bullit sits, I mean if you seat a bullet and check for runout, then pull that bullet, turn the neck and reseat isn't the runout going to be the same?
I'm sure this is a simple concept I just cannot visualize it.

OK - here goes-

Before neck turning, you have a neck that may be "bumpy" on the inside and outside. By running the neck down a slightly oversize mandrel (often .001"), you force the inside of the neck to be "smooth", because it now matches the mandrel. All of the "bumps" have been "pushed" to the outside of the neck.

You are now ready to knock off the high spots that exist on the outside of the neck.

Make sense?

To add to the above,

You have now created a smooth cylinder for the bullet to rest in. The neck should be of consistent thickness.

As for the runout you discuss, I don't quite understand the "pull the bullet" part of your question. I believe you may have a question about runout during seating - this may be caused by a die that does not seat the bullet "square". By seating the bullet, then physically "turning" the bullet while still in the shellholder, then re-seating, you may find runout decreases.

Hope that helps.

if you pull the bullet, neck turn, then replace bullet, runout should be the same.Forget that. A loaded round that has been neck turned will work this way. You should only size the neck part of the way. The unsized part of the neck will expand on firing to the dia. of the rifles chamber in the neck area.. This unsized part of the neck centers the round in the chamber. Bushing dies without an expander work best.

I think there are a couple of issues here. First inside and outside neck turning do two different things, but are driven by the same idea from an accuracy and safety standpoint. Ultimately, you want the case to be held in the best possible alignment with the bore. Bench rest shooters do this by having the chamber neck only barely over the fired diameter of the neck. That is what is generally referred to as a bench rest chamber, and if you are having a gun built for a PPC, 6BR, 6x284, 6x45 etc, you need to make a decision as to which chamber you want. The problem is that all brass used in a tight necked chamber needs to be turned so that a close tolerence is held. If the neck is .001 to large, and forced into the chamber, dangerous pressures will result.

Normal chambers are much larger and technically you should never need to turn case necks for safety reasons unless you are using brass converted from another caliber, such as a wildcat or making, say, .270 brass from 30/06.

In instances where you have a normal neck chamber, outside turning is all that is needed, when brass becomes too thick. With a tight neck chamber, tolerances are so tight that brass needs to be adjusted both for thickness and final neck id to control both concentricity and bullet tension for best accuracy. This is done by sizing the case, outside neck turning (which by its nature is always done with some type of mandrel) followed by inside reaming to the optimum ID for bullet tension. This is always done with new brass for a good reason. Remember the concentricity issue. If you fire a cartridge with an off-center neck in a tight neck chamber, the entire cartridge will expand offcenter. At that point, neck turning will do little good for accuracy, since the entire cartridge is then assymetric to some extent and will never center up. The idea is to make the neck perfect, let the neck hold it straight in the chamber, then fireform a concentric case.

This is why neck turning seldom does any good in a non-target rifle. Unless it has a tight chamber neck, the cartridge is never centered anyway. Neck turning in hunting rifles is generally only done for safety reasons when brass thickens. What generally helps more is to have a long bullet or one seated out into the throat. The throat is generally a .002" fit to the bullet and very consistent. If enough of the full bullet diameter is in the throat, it will align the cartridge and do the same thing as a tight neck. I have long believed that this alignment accounts for a lot of the accuracy observed when seating "close to the lands". One anomaly is that with wildcat cases, you sometimes get a "ring" of brass at the bottom of the neck on the inside when necking down. I have seen this with .416 Taylor. This is best removed by inside reaming.

There you have it, ouside turn for target rifle accuracy and safety in hunting rifles, inside ream for bullet grip in target rifles. The mandrel issue is just part of the outside turning process. The "mandrell" that smooths the inside neck is actually the sizer button in your sizing die. Most of this info is available on the reloading equipment web sites, such as Sierra's tech bulletin section.

Thanks for the info. It sounds like since 99% of my concern is about hunting rounds I would not serve any purpose to turn the outside necks. I do like the confidence that a tight group provides but I do not have a "bech rest" gun so my quest continues. Once again thanks, there will be more questions later I'm sure.