Neck Turning and Chamber Size

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ArtP

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A local reloading buddy bought a used, custom 6MMbr rifle and Redding custom competition dies. The chamber size is stamped on the bbl at .262. He has no live ammo, but a few spent cases from the previous owner.

New, uncut Lapua brass with a bullet seated will not chamber, neck measures .270. Empty brass will seat with some difficulty, but grow back to .270 after seating. It wasn't surprising to see the previous owner had neck turned his brass, with the naked eye the walls are thinner (both Lapua).

A. Would you have the chamber reamed to "normal" size, what would normal be? Or would you turn necks? Besides the hassle and thinner brass walls, is there another consequence? Brass life?

B. He needs a bushing for the Redding neck sizer. The direction call for measuring a loaded round, which we don't have, and go .001-.002 under. Knowing only the chamber dimensions, how much smaller should the neck bushing be?
 
That's going to depend on neck thickness. But I'd go with .001 under chamber size then you can turn them down till the loaded rounds are the desired diameter
 
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You will have to neck turn, or ream, or both, to make a loaded round fit the custom .262 necked chamber. Don't try to cut it too close at first.

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Jerkface: Further turning is only only going to thin the neck more. The bushing needs to be the right size

Walkalong: I understand. If the neck turn option is chosen, which size bushing would you get? The bushings can run $25 ea. and I'm sure he'd rather not have a collection.

From what I've read, there should be enough room for the neck to expand to release the bullet.

I'm thinking .258 or .259, get the thing operational, perhaps go slightly tighter later.

FYI - the spent, turned brass is .265, no idea it's size pre-fire.
 
The bushing won't change the size of the neck of a loaded round. All it will do is give you neck tension with a turned one. If you have some that are already turned you can just measure the inside diameter of the neck. You know it had to be small enough to hold onto the bullet before it was fired. So say it was .242 see what it is now then subtract that difference from the outside diameter and that's your bushing size.
 
JF: True about the tension, I was just thinking that. I'd need some sort of ball micrometer to measure either wall thickness or ID.

I have a 243 (shoots same bullets) and can measure pre-fire, post-fire and loaded rounds. The problem is I don't know the chamber dimensions of my rifle. Without the chamber dimensions, this is algebra but solving for two unknowns.

What I have learned elsewhere is a "no-turn" chamber in 6mmBR is .272, or 2 thousands larger than a loaded round (unturned). It leads me back to .258 being the right bushing. 2 Thou for spring back and another 2 thou for snug, but not over-tight chambering. Thoughts??
 
I haven't loaded any 6 PPC in some time, but just looked and one sizer has a .257 bushing and the other has a .258. I also have a .259 and a .260 bushing.

I have a .262 bushing in the Niel Jones hand seater die. I also have a .261 bushing.

It is hard to not end up with more than one bushing. :)

.2433 (Pressure bump/ridge) + .0084 + .0084 = about .260 That gives very little wiggle room, but a .258 bushing would be about right.

I would suggest turning necks to no more than .0075 and end up with .002- clearance all the way around. That is still tight.

It's tight enough that you need to know precisely what diameter the bullet is at the base. Most custom Benchrest bullets are the correct diameter with a pressure bump at the base. You'll need to know the exact diameter of the bullet being used and turn your necks to the nearest .0001. Or don't cut it so fine at first.
 
With Custom Benchrest 6 PPC bullets most of the bullet is .243, but right at the base is a pressure bump from the forming die. It will be in the neighborhood of .0002 to .0004 IIRC. When cutting it real close in a tight necked chamber it must be taken into account. I haven't seen any factory bullets with this. Just have to check the bullets you have/will use.
 
Ah thanks! I think he'll be using mostly Berger and Sierra. Going a little on the loose side, any pressure bump shouldn't matter.
 
Walkalong - that is a very nice micrometer. My dad was a old school machinist and I remember that brand. I have a crappy digital micrometer, or caliper I think is a better word. I've wanted to upgrade for a while.

A quick Amazon search doesn't turn up anything above the rest. Can you make a recommendation for an analog caliper?

Oh look, I hijacked my own thread. LOL
 
Mr. Walkalong is certainly on target with his recommendation of tube micrometers for measuring case neck thickness. Attached is a variety of such instruments that I keep around my shop for measuring necks and similar chores. There is a variety of such instruments available in a wide range of prices. The one I particularly recommend is the modified Mitutoyo tool sold by KM (Who also make neck turning tools, etc as previously noted). The advantage of their modification is the tip of the spindel is reduced, making area-specific measurement more precise. (Shown upper right in attached photo.) Also shown is another fast and accurate type measuring system in use. Though tools of these types may be convenient, they are not at all necessary to accurately measure case wall thickness. The accurate and simple "Old Reloaders" method is simply measure the case neck with a bullet seated, using a standard micrometer. Subtract bullet diameter from reading, divide remainder by half and you have wall thickness.
 

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The one I particularly recommend is the modified Mitutoyo tool sold by KM (Who also make neck turning tools, etc as previously noted). The advantage of their modification is the tip of the spindel is reduced, making area-specific measurement more precise.
A very good point. The style I have is limited as it won't get down as close to the shoulder.
 
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