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.

Simdow,

Turning the case neck does not change the position of the bullet in relation to the case. Weither your neck is .008" thick or .015" thick, the bullet, in a perfect world and with good equipment will be perfectly centered in both.

Turning the necks changes the relationship between the case neck and the chamber wall allowing a relief when a round is fired.

Say your neck in your chamber measures .262" like my 6mm-284 does. If I take a factory 284 case and neck it down to 6mm, the outside neck diameter with a bullet seated will be to large to even crush fit into the chamber. This is so even though bullet run out is in the 0.001 to perfect range.

If I turn my necks down to 0.0085", and seat the same bullet to the same depth or position, the bullets relationship with the bore is still the same as before, the only difference now is that the case neck will have around .001" bullet release when the round is fired, allowing the bullet to stay basically perfectly in line with the bore and still easily slide from the case neck.

Once the round is fired, this turned fired case will not even touch the neck in a conventional 6mm-284 sizer simply because the turned case necks are far to small in diameter even after firing.

Because of this a special sizing die, I like Redding competition bushing dies are needed to size the smaller neck just right.

Turning case necks adjusts the necks relationship to the chamber, not the bullets relationship to anything else.

This is a way to custom fit your brass to your chamber and often produce more accurate groups.

One does not need a custom tight chamber for this either. Many shooters looking for top accuracy out of factory chambers often size larger caliber brass down to their factory chambering for a custom .001-.002" neck fit.

One example is using 30-06 brass in the 25-06. Sizing the larger neck down to .257" will thicken the neck, taking up the slop in loose factory chamberings. Then turning these necks will produce concentric case necks by removing any variation in neck thickness from sizing down.

This is what neck turning does, allows custom tight, 0.001"-0.002" neck to chamber fit and removes any neck thickness variations. This is why using match quality dies with neck turning can produce rounds with bullet run outs in the sub 0.001" range consistantly.

Without either of the two, your bullet run outs will increase dramatically.

Good Shooting!!

50

fiftydriver,
Thanks for the explination it really helps. I've not been doing this verylong, and had not really considered neckturning until recently, I've just been setting aside cases that were not concentric.

simdow