I have a 8mm REM mag case, and I'm try to figure out the minimum case wall thickness when turning it down. What do you think the minimum thickness can be before something bad happens?????

Don't turn down to the minimum amount possible. It will accomplish nothing except hurting your accuracy and reducing your case life.

The required amount of neck turning should be dictated by only two factors -- whether or not you are: (1) turning for a factory chamber with generous clearance, or (2) turning for a tight necked, custom chamber.

If turning for a factory chamber, turn as little as possible. The goal is to turn just enough to clean up the necks to make them consistent thickness. No more than 75% of the circumference of the neck should be sufficient, the theory being that this should be sufficient to achieve good enough uniformity.

If turning for a tight necked chamber, you'll need to take the necks down enough to ensure clearance for bullet release. You'll also need a ball micrometer to accurately measure case neck thickness. I would recommend leaving at least 1.5 - 2 thousandths total clearance for a tight necked chamber, but the amount you need to turn will be dictated by the diameter of your chamber's neck.

Martindog

Turn so that a case that has been over the expander is .001-.002 larger than a sized case that has not been over the expander. That is, size the case with the expander removed and measure that then after sizing with the expander in place turn to .001-.002 larger than the unexpanded size. This if your chamber is standard. This will give you adequate grip on the bullet. For a light recoiling rifle you may match the diameters so that the expander just brushes the neck.
If the chamber is tight necked then of course the neck dia establishes the thickness. Regards, Bill.

Do you think the best method of neck turning is outside or inside? It's a 8mm necked down to 30cal. So the case gets resized, I have been turning only fireformed brass after resizing.

How much variance of wall thinkness do you think you should see?

Thanks for the help.

This is all very confusing. Turning is only necessary to make sure you have adequate clearance. You can turn to even necks, but I've not been able to find a benefit in a factory rifle.

For accuracy purposes, turning is better than reaming. For speed purposes, reaming is better.

To determine how much to turn, measure a fired case from the rifle. Then, turn the neck until your loaded round measures .002 to .003 less than that. Go with .003 on a hunting rifle.

Then, get a Lee collet die or a Redding Bushing die to keep from over working your brass.

Any more clearance than that, or standard neck/expand dies and you are over working your brass. JMO, Dutch.

[This message has been edited by Dutch (edited 11-21-2001).]

Dutch,

How can you tell if your over working the brass when resizing and neck turning?

Are there stress signs to look for?

Woody

TGW, anytime you "work" or resize brass, you cause something called "work-hardening". The movement of the metal actually changes the grain structure of the alloy. This is not easily "seen", but one of the characteristics of work-hardening is "hardening". The brass gets harder, more springy, and takes more force to deform. It also gets brittle. However, case necks can be annealed. If done right, annealing changes the structure back to where it should be, and the cycle starts over.

Now, if you have .01 clearance, you move your metal more than if you have clearance at .001 (I did make a typo earlier in the post above!). So, (this is a simplification, of course, but close enough), if you move your necks back the .003 clearance you created at firing, plus .002 more you need so the bullet will stay in the brass, you size the brass less. That's what you do with a bushing or collet die.

With factory chambers, brass and dies, you end up with .015 clearance between the loaded round and the chamber, so you have to size down at least that much. Then, you use a standard die, which squeezes things down another .01 to .02. Then, the expander ball expands it BACK about .01. And, the kicker is, the less clearance you have in the chamber (in other words, the thicker your neck brass), the MORE the standard die has to squeeze it down, since it sizes the OUTSIDE. It has to squeeze it down, because the die is made to make sure it squeezes the thinnest possible brass down enough to hold the bullet.

To add insult to injury, dragging an expander ball through a thick neck that has been squeezed down "good" is a certain source for concentricity problems.

So in a factory chamber arrangement, you either work the brass upon firing, or during sizing. And usually in the range of .025, which is a LOT, about five times more than a reasonable "tight neck" arrangement.
Again, over-simplifying things, that would mean that a factory rifle that would show cracks in the neck (the usual result of "overworking" brass) in 5 reloads could turn in as many as 25 loads in a tight-neck configuration.

Dutch:Know you�ve done it. .. :~/

I understand the concept of �work-hardening� but I have not heard the term of �annealed� maybe you can clarify this for me.

This is what is going on with my brass in the outside measurement of the neck and the wall thickness. I�ve measured Fire Formed, Resized and Turned cases and this how it measures:

Fire Formed - .3392 w/wall .0145 +/-
Resized - .3352 w/wall .0154 +/-
Resized & Turned - .3334 w/wall .0133 +/-

Now the comparisons:

Fire Form vs. Resized & Turned = .0058 w/wall .0021
Fire Form vs. Resized = .0040 w/wall .0009

The Turned case have a more consistent wall thickness on average, but seems to have more clearance to the chamber. But has better concentricity.

�Now, if you have .01 clearance, you move your metal more than if you have clearance at .001 (I did make a typo earlier in the post above!). So, (this is a simplification, of course, but close enough), if you move your necks back the .003 clearance you created at firing, plus .002 more you need so the bullet will stay in the brass, you size the brass less. That's what you do with a bushing or collet die.�
So if I�m understanding you correctly, the .003 + .002 = (.005) the above comparisons falls within this value +/-.
Thanks for the help and HAPPY TURKEY DAY!!
TGW

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Where ever you go. .. there you are.

Geez, I feel like one-eye in the land of the blind for minute here. I'll get over it...... There, there it went. .

Annealing: this is different for ferric and non-ferric metals. For brass, it means heating the metal to about 670 degrees, and quenching it in cold water, immediately afterwards. Lots of descriptions on the net, including "heating to a cherry red in a dark room". This may get you close, and it may get you hurt, as it is VERY EASY to get your necks so soft they won't hold a bullet.

When annealing cases, you anneal the neck ONLY, and quench the case before the heat travels to the base of the case. You don't want a nice, soft case head, do you? Right. The Hornady kit comes with a bottle of tempilaq, which is a liquid temperature sensitive indicator. It's the tempilaq (or welders crayons) which keeps you out of trouble as far as too hot or too cool.

Now, as far as I am concerned, your clearance on your necks is fine, unless you are trying to shave your last .1" off your accuracy. You have .004 clearance before turning, which is within a hair of ideal. The only dimension you are missing is the one of the loaded round, but if the bullet is holding, and the neck has enough clearance to release the bullet upon firing, you are good to go there.

The only comment I can make is that you have turned your brass down about .002 (.001 on each side), which may have been just a little more than you need. For sporters, the usual advice is to set your turner to just "knock off the high spots". That is, leave about 25 to 50% of the neck alone, and just turning off the highest little bit. It takes a little trial and error, since the setting varies from case to case, but it saves work and work on the brass. HTH, Dutch.

Dutch:

You may have felt like a one-eyed man in the land of the blind, but with all your help and sightful input I been able to limited the amount of time I have to wear my dark welding goggles.

Thanks for all the help,
TGW

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Where ever you go. .. there you are.