I just bought the Sinclair neck turning kit. Now what? How do I determine if a case needs turning? if so, how much? What am I trying to accomplish? (Yeah, I know, accuracy) What to measure and how? Guess I should have know all this before ordering but it was one of those things I always wondered about. Thanks....Mike

Normally I only neck turned for a tight necked custom chamber and turn to a set OD. In a factory chamber with factory dies you might be causing yourself more issues if your dies can't give you enough tension.

I wouldn't jack with it in a factory chamber.

If you are shooting cartridges in a factory chamber with no problems, there are only a couple of reasons to neck turn.

1. If you are using some other brass necked DOWN you my need to turn the necks to where they are only .001" or .002" larger diameter than factory cases (with a bullet in place). That can make your cartridges fit the neck a little better in the factory chamber and still release the bullets without building up excessive pressure. BUT, you need to be careful you don't get the necks too thin or leave them too fat. Someone experienced in neck-turning should preferably walk you through the process, with you doing the work and them guiding you the first time or two.

2. Assuming you are using correctly headstamped brass for your chamber with the necks unaltered and are experiencing no problems with it, probably the only neck turning you could want to do would be to make the case necks a bit more even thickness all the way around. To do that, adjust the turner so that it only takes brass off the necks for 1/3 to 1/2 of the way around the necks. That will be the turner reducing the thicker parts of the necks but not touching the thinner parts.

That means your case necks will be more uniform thickness all right, but it may or may not give you any noticeably more accurate shooting.

Other than those two reasons, you probably won't have a need (or even a practical application) for turning the necks of factory made cartridge brass for the chamberings you are shooting.

At least you now have the tool if you ever get a custom "tight-neck" chambered rifle and really DO need it.

The way to determine if your brass "needs" neck turning is after you have fired a round will a bullet slip into the neck of the fired cartridge. If so, you don't need to turn necks; if not, your necks have gotten thick and you do need to neck turn. Usually by the time they get that thick --assuming a factory rifle-- you'll be experiencing other problems and it's easier to pitch the whole lot and start over.
When I was shooting factory rifle matches, I would neck turn my brass. I didn't need to as far as the dims of the chamber but I did it for a more uniform neck and a more uniform bullet pull. It gave me a very slight but measurable increase in accuracy. Slight enough however that I certainly wouldn't do it as a routine thing with my hunting ammo.
Before you can reap any advantage of doing something like that,(and weighing cases and bullets and uniforming flash holes, etc) you need to have a very precise bench set-up and be well grounded in your own bench technique. You ain't gonna notice any betterment shooting off of a rolled up poncho or a couple of sticks.

Size neck down. Expand with mandrel. Make a cut so it shows on the entire neck. Dont cut into the shoulder. Use brass with bushing die, no expander. Redding type S FL die.

Thanks guys. Guess I should have asked before spending the hundred bucks.

I'm gonna disagree with 243. Assuming you're not cutting to a needed diminsion for a custom chamber. I set my turner to "clean up" around 75% of the neck. I agree that you don't cut into the SHOULDER.
Thanks for pointing out my "mis-type".

And I am going to disagree even more strongly with 243. In factory chambers the case necks of factory spec brass are already loose in the chambers. That's because the SAAMI factory MAXIMUM diameter of the case necks is about .003" smaller than the SAAMI MINIMUM chamber neck diameter.

If the cases are within acceptable manufacturing tolerances but a bit smaller than SAAMI max, they will be looser yet. If the chamber is within tolerance but larger than SAAMI minimum, that will cause still more looseness of fit.

If you turn the brass all the way around the neck, it will be an even sloppier fit in the chamber than it began, which will very seldom help accuracy.

If you are shooting enough that you get to the point where a bullet won't fit in the fired (and thickened) case neck when it has not yet been resized, THEN you will need to turn case necks as was pointed out by Wasbeeman. And then it will be reasonable to turn the necks all the way around to get a uniform proper thickness which will fit the chamber with enough looseness to release the bullet on firing. But until then, all-the-way-round turning is not needed or necessarily a good idea with factory spec chambers and factory brass made for those chambers.

Everyone marches to his own drummer, and that is the beat mine plays.

A bushing die can size 1/2 of the neck. The unsized neck fully expands to the neck chamber area in about 3 firings. This centers the round/bullet in the chamber. If you only turn 75% it will be off center as the neck wall thickness is not the same. Factory 243win Chambers in 40x & Rem 600. Just my results from shooting & testing many rounds. These 3 bushings work well with unturned or turned brass.

I agree that partially resizing the neck will create a centering "doughnut" at the shoulder of the case. That will effectively counteract any increased space between the neck and the chamber walls. I do that.
However, when you speak of setting your turner to where it takes off 100% of the surface of all the cases as opposed to a simple uniforming of most of the neck, you're talking about how many angels can dance on the head of a pin.

For a factory rifle, I personally would not spend $100 for a Redding bushing die with any number of bushings after spending $100 for a case neck turner. Just spend the $200 on good brass to begin with anyway. Or in your case, just the other $100. I do have a case neck turner gizzy for my Lyman case trimmer, but I can say I only used it to see how it worked.

This is one of those thingies that keep tool makers in business. And I think everyone should neck turn. At least once.
Take 20 new cases. Fire form them. Then neck turn 10 and leave 10 untouched. Fire a single 10 shot group with each batch. Do that a couple of times. How do the groups compare? That'll give you your answer.

Hey Mike

I turn necks for 3 different rifles but they have custom tight necks and a factory case will not go in them. For a factory rifle you are wasting time and money. Exchange the turner for primers and powder.
If you have a caliber that Lapua or Nosler make brass for then buy the expensive brass are you are good to go but still may not see much difference on a target.
Good Luck