*Article* Should I Outside Neck Turn My Brass?

[John Y Cannuck]

[h=1]Should I Outside Neck Turn My Brass?[/h] Posted on October 4, 2012
Written by Ballistic Technician Paul Box
This is a question we get just about every week. Should I neck turn my brass? Well, the answer can be yes….and no. Let’s look a little deeper into it.
Naturally, if we had our favorite gunsmith chamber a rifle with a “fitted” neck we’ll have to neck turn in order for it to fit our chamber. But what about a standard SAAMI spec chamber? This all depends on the quality of your brass. Namely your case neck thickness variation. What I do is take a ball Mic and check the case neck thickness at “8:00 o’clock, 12:00 and 4:00 o’clock points. If my thickness variation is .001″ or less, I wouldn’t outside neck turn. Unless we’re shooting 1,000 yd. benchrest I don’t think you’ll see any difference in accuracy if this thickness difference is any smaller than that.
Our main goal in outside neck turning is to give our seating die it’s best chance to seat a bullet with good concentricity with as little of run out as possible. This puts our bullet in better alignment with the center of the case body and in a squared and trued action, more perfect alignment with the bore.
Brass that has a neck thickness difference that’s more than .001″can be turned down to this spec and will shoot fine. They’ll also have the advantage of not being too thin, which will give early case neck splits and short case life.

http://sierrabullets.wordpress.com/2012/10/04/should-i-outside-neck-turn-my-brass/

 

[kombayotch]

While I agree that neck turning can improve accuracy in match chambers, I don't buy into this commonly held belief that evening out the thickness of necks is the reason for the accuracy gain. My own experiments and measurements with my Pressure Trace system have lead me to conclude that it's the removal of the burr around the case mouth that is found in new cases or ones that have been tumbled in SS media. This burr is extremely difficult to remove with a chamfering tool (even a VLD one like the K&M). I believe the fact that this burr is removed by neck turning is being overlooked.

 

[paperslayer]

They allude to it in the article, but most SAAMI spec is 5 thou clearance. If you have a factory chamber and you have 5 thou clearance, you should not be turning. I like my necks with 1-2 thou but them I am single shot feeding.

If you have a custom chamber in a custom barrel, and you know the neck dimensions, then turning to clean them up is one in the bag for you. If you want to get by with the best possible results and not turn, use Lapua brass and have fun. On the balance, only if you are minimizing variables in all other areas (including annealing) then turning necks, chamfering and deburring case mouths is probably worth it. otherwise probably not worth it


My target rounds have it done. Hunting and varmint rounds do not.