Neck turning and chamber sizing

[Quicksilver]

Im building a custom 7 Rem Mag and want to really squeeze every drop of performance out of it, so I thought I would venture into the neck turning territory. I've been meaning to start neck turning anyway to get more consistent neck tension and avoid donuts anyway.

My question is, what do I need to pick up to do neck turning, and what reamer should I select for my new build? How do you determine reamer sizing from neck size? How much clearance do you want?
Do you neck turn the brass for just the first round, or do you have to resize and neck turn the brass every time you resize the necks?

I need a old timer to school me on how this works. I do my own loading now and have various little BS rituals for sizing, neck sizing, annealing, flash hole deburring, ect but now I need to put neck turning into the mix.

Normally, I use Winchester brass, but for this rifle, I will buy only fine/top notch components (lapua brass) and plan on using the 162g AMAX as my only bullet with CCI magnum 250 primers. Haven't thought of what powder to use yet, but Ill burn that bridge when I get there.

 

[Quicksilver]

Neck Turning Basics

I did read this, but it didn't really answer my questions (Im a machinist/mechanic/engineering student, in that order) but gave me alot more questions.

 

[lightman]

I would call Dave Kiff at Pacific Tool and Gauge about a reamer. The link above is a good one to read. Also, google Varmintal, and check out his reloading page. He explains neck turning really well. You will need some type of measuring tool like a tubing micrometer, a neck turning tool with a mandrel, a expander die with a mandrel, and a way to spin the case.. I use a cordless drill and a set of case holders from Sinclair to spin the case.

I'm not sure if Lapua makes brass for the 7mag. If this is important to you, you may want to check. Lightman

 

[witchhunter]

The most common mistake of turning necks is turning too much. I adjust my cutter to just clean up the neck the first time. It shouldn't cut all the way around the neck, only the thick side. This will make them concentric. Then after that you can adjust for the neck tension that you need for accuracy. Each chamber is different. You will have to experiment and you will lose some brass in the process, but once you find the size, you are good to go.

 

[ZiaHunter]

The Neck Turning Basics is a very informative piece and covers most of what you need to know. Buy a good neck turning tool such a Sinclair NT4000 or the 21st Century neck turning tool. I have both and like the 21st Century when paired with the lathe and a cordless screw driver. Neck turning is a PIA but the lathe speeds things up considerably. A tube micrometer is a required piece of equipment in order to accurately measure neck wall thickness in setting up the tool. I have the Sinclair/Starrett one and it measures to .0001. I would go with the carbide turning mandrels since they will provide more consistent neck thickness.

I turn necks for my precision rifles (bolt action) most of which were cut to no turn dimensions. The main reason I turn is obtain consistent neck tension and concentricity. Once a neck is turned there is generally no reason to do them again and turn new brass as part of the initial case prep. I turn my necks to a uniform thickness for a specific caliber. For instance all my 6.5 CM brass has a neck wall thickness of .013 and depending on the lot varying amounts of brass will be removed from the neck. If you will be just turning for one caliber, once you decide on the proper thickness don't change it. Buy good brass since their neck wall thickness is generally more uniform. With less expensive brass you will have to cull a fair amount of cases since the neck wall thickness may vary by more than .001 which will prove problematic or the necks will be too thin to turn.

The Redding Type S dies will provide consistent neck tension and good concentricity with neck turned brass and there is no need to use the expander.

 

[damoncali]

Buy the brass first, and measure the neck thickness of a good sample - say 20-30 pieces. A tube mic is the best way to do that, but a good one is expensive. Calipers are not ideal due to the curve of the neck. What you're looking for is the thinnest neck you can expect from your brass out of the box. Plan on turning it to .0005-.001" thinner than the thinnest piece you measured. Then, your chamber neck size should be 2 x (turned thickness) + bullet caliber + diametrical clearance. Diametrical clearance is a judgement call. Benchrest guns have been known to run less than .001". I have a 30BR with .001" clearance. That's pushing it, honestly - you have to keep it clean and load it with some care (not that you can't do it quickly). What's cool, though, is that the brass doesn't really grow after firing. It's pretty damn close to the same size it was when it went in the gun. Brass lasts for damn near ever. For my high power rifle (bolt gun) I like to use .004-.005" clearance. That gives you a little room while still providing good brass life. So if you know you're going to be turning your necks to .012, and you're shooting a .243, you would get a reamer with a neck diameter of .012 + .012 + .243 + .005 = .272. Then decide what bullet weight you want to use, and call up the reamer maker and ask them for a reamer with that neck diameter (.272 in this example) throated for whatever bullet you want. 9 out of 10 times, they've done it before and can tell you what you need for the throat. "I need a .243 Winchester reamer with a .272 neck throated for 107 grain SMKs" - that should be enough to get you going unless you want something weird. If you're shooting something common, there may be an off the shelf reamer that is exactly what you want or close enough.

I use a Sinclair tool. It works just fine. I don' think the tool matters. I do every piece by hand so I don't have to worry about heat build up, but some like to use a drill to speed things up. Just go slow and check your work along the way. Once you get the tool dialed in, they tend to stay set. Don't change it unless you have to because it's a pain.

 

[Quicksilver]

So, if your bullet loaded in case measures .314 with neck turned brass then you can say the chamber needs to be at .316 or do you want more clearance?

Also should I buy Nosler, Norma or Hornady brass? I've only had experience with Hornady brass so I dont know about the others.

 

[damoncali]

With a loaded, turned round measuring .314, I would want a .319 neck. You can go smaller than that, but there is little benefit to doing so. My .30BR benchrest rig has a .330 neck, and the loaded rounds are .329. That's too tight for general use. I would shoot for loaded diameter + .005". Tighter than that and you're making your life harder (and potentially more dangerous) for diminishing returns. Anything from +.004 through +.007 is about right.

Too much clearance, and the brass expands too much. Too little, and you have to start worrying about interference with crud/fouling, making sure that ALL your ammo will fit, etc. +.005 is a good compromise, and makes for stress free reloading and shooting while still giving the benefits of a tight neck.

I haven't used Hornady or Nosler brass. Norma is good. You can see what sort of variation you will get here (I measured a batch of Norma 6XC every way I could think of): http://bisonballistics.com/articles/norma-6mm-xc-brass

 

[steve123]

Decide if you want to ever shoot unturned necks in that rifle again first. Both unturned and turned necks can be used if you have a tight neck chamber of the appropriate dimensions.

A good compromise is turning .002" off of necks which should give a full clean up and use a chambering reamer with .002-003" more neck expansion than a loaded round. I have over 10,000 rounds downrange in differing field conditions with not one problem using my chamberings done up like this. The necks last forever too, especially if annealed. Actually the primer pockets will loosen up before any neck will split.

 

[Quicksilver]

SAAMI spec is .317 at the "front" next to the shoulder and .316 at the end of the brass for the 7 rem mag chamber-

I was thinking a .315 reamer would be a good compromise for still being able to chamber factory stuff but still chambering neck turned brass without having the necks expand too much after each firing.

Gonna go buy some brass and see how thick it is, and load it up and see where it falls and go .003-.004 larger for the chamber.

Instead of using RCBS dies for the 7 RM, I was thinking of ordering custom dies with a different neck diameter to play with the neck tension. Any recommendations?

 

[Goin'Hot]

Instead of using RCBS dies for the 7 RM, I was thinking of ordering custom dies with a different neck diameter to play with the neck tension. Any recommendations?

I had Neil Jones make my custom FULL LENGTH SIZING DIES. Excellent craftsmanship. Be forewarned, they take a good bit of time to be made.

 

[Quicksilver]

Take a look at this chamber print (first is SAAMI, second is a custom chamber someone had made) and why would the lead in angle be better?

7mm Remington Magnum Chamber Print | PrecisionRifleBlog.com

I think im gonna have my builder just put my stuff on hold until I can get about 100 pieces of brass, everything to turn necks, then measuring out all the brass, finding the lowest, going down .001 from that and turning all necks, then loading in a bullet to determine what it will be at the neck loaded, THEN going .004 larger for the chamber, THEN coming back after all that and ordering dies to get the neck tension at .001-.002

Sound reasonable?

 

[Goin'Hot]

If you have Neil make your dies, he'll send you dies to start loading with. Once your rifle is built, you fire a couple pieces of brass 3 - 5 times without sizing and then send the brass and sizing die back to Neil. He finishes the die and Viola! perfect die for YOUR chamber.

My chamber is just a "clean up" chamber. The reamer was 0.338". A loaded round measures 0.338" so, I turn to 0.3365" or 0.0015" clearance. I should never have a neck split.