Neck Sizing Vs. Full Length Sizing and Neck Tension

Veteran

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I have not guaged the head space, but the Encore is a breach loader, so I don't know how that may factor into it.
Once I began having all the case head separations, I did google this online and what I found was it was fairly common and fairly widely reported in belted magnums that are full length resized. Most report only 2-3 firings before failure of the brass because its being worked back and forth so much and fatigues at the juncture just above the belts on the belted magnums. The metal gets shoved down until it hits the belt and has no where to go, then it gets elongated from that same point in the next firing. The best idea I heard here was to full length resize with a .002 shoulder bump that may ease some of the back and forth further down the case at that juncture. So, I will try that. If it doesn't work, I will then have no choice but to go back to neck sizing only on belted magnums I suppose....
 

Starlite

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Belted brass can be "full length sized" after fire forming in YOUR chamber by simply measuring and "bumping the shoulder back. 002-.003". Oftentimes, setting up a full length die as the manufacturer states on a belted cartridge creates excessive space between the cartridge shoulder and the chamber shoulder which in turn causes the head separation issue you speak of. It can be overcome as others state by fire forming it and then treating it like a non-belted cartridge. Chambers were often cut this way to provide ensured chambering, especially when hunting dangerous game.
As far as interference fit, which many call "neck tension", it is a variable and is often determined but many other factors such as SAAMI chamber or custom, neck wall thickness, cartridge neck to chamber clearance, annealing, bullet jump/jam, bullet type (jacketed vs. mono), etc..... Many use a Lee factory crimp die to adjust "tension" and find that it is another tool to help improve consistency. Due to all the above mentioned factors and more that others will likely specify, each rifle is unique and may take a little tinkering to get cartridges to shoot best in your rifle.
Fully agree.
I use Lee crimp dies for my 6&6.5 creedmoor, 270Win and 223win. I’ve done extensive testing with cannelure pills, non-cannelure and monos with and without crimp. Most of the time I get similar or better results with a crimp. I think this is because I’m generally getting more consistent neck tension. Likely because my dies size with a elliptical ball mandrel.
In my opinion any magazine loaded magnum cartridge for hunting should have a minimum of .003”-.004” of tension and be crimped, especially if it’s a cannelured projectile.
Just my 2c.

“Fail to Plan-Plan to Fail”

Also OP FWIW I do a lot of bench rest shooting (single feed 95% of the time). My loads are all neck sized with.001” of neck tension. Different techniques for different situations. I’d suspect some hunt this way too. Not my style but if it works then who am I to say.
 

Hugnot

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I F/L size everything. I want easy chambering but adjust head space to within .004 inches.

For belted magnums I F/L size & adjust headspace at the shoulder. I use a .005 feeler gauge (Husky, Home Depot) to set up my F/L dies with the shell holder for belted magnum reloads - gently set the die down on the feeler gauge that is on top of the shell holder. No head separations & brass primer pocket expansion causes discards. Loaded rounds feed from magazine into chamber quick & easy.

I use either Redding bushing or Forster F/L dies and usually turn necks. For wildcat rounds like the .20P, 6mm-06 or 6.5-06 I always turn necks. The Forster dies get sent back for neck portion honing/enlargement after I figure out brass/chamber interactions.

I anneal after every 4 cycles - this makes for consistent neck tension & removes most brass spring back that causes neck tension variation.

As for crimping - yes, AR loads & .204 loads as my .204 gives is most accurate with bullets seated up near rifling and that gives less than .125 bearing/neck contact

Not rocket science.
 

okie man

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3 very important reloading terms. 1-Neck sizing, the sizing of the neck only. 2-Full length sizing, when you size the neck, shoulder and body of case. 3- excessive head space, when a chamber is over sized or the cartridge case is too small from over sizing it.
 

Veteran

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Here is video clip from Jeff Brozovich of LRO on bumping the shoulder.

I like this approach because it just means changing shell holders to size the brass more or less with thicker or thinner shell holders and keeps me from needing new dies. My only issue is 1) no bolt because the Encore is a breach loader.....but I will maybe try this trying to open and close the breach each time with some feel, and I will measure with a micrometer at the same time to sort of home in on it. Nice approach. Thank You.
 

Tiny Tim

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I get that I’m overly focused on just this one point. A magnum is headspaced belt to bolt face, so the firing pin/ejector doesn’t push it forward until the shoulder touches, usually. In a normal headspace gun, the belt should touch first with new ammo.

Upon firing, the case expands forward mostly to meet the chamber and of course and head clearance allows minimal rearward expansion.

Without annealing, I would expect neck and shoulder cracking as a failure from all the work hardening.

Since your cases fail by head separation, I’m thinking your headspace is NG. Have you gage’d it? I say that because the case would get pushed forward, fire, expand, then the head area(due to excessive head clearance) is expanding back to the bolt face excessively, over working the head.

Anybody else see case head failures on magnums as common?
I think what happens is that in the process of FL sizing some belted cartridges, the shoulder gets pushed back more than you think. I've heard of .012 -.018. Still head spacing off the belt. When fired, the brass stretches near the head rather than only at the shoulder. This in turn causes head separation. Not saying there isnt some other issues in what I just described. Just saying it happens.
 

nksmfamjp

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I think what happens is that in the process of FL sizing some belted cartridges, the shoulder gets pushed back more than you think. I've heard of .012 -.018. Still head spacing off the belt. When fired, the brass stretches near the head rather than only at the shoulder. This in turn causes head separation. Not saying there isnt some other issues in what I just described. Just saying it happens.
How would that stretch at the head? If belt to bolt face were in spec, this area moves about 0.001”. If the shoulder is oversized, it blows forward. Hmmm…
 

brant89

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Like many others on here, I FL size everything. I set my dies up to just close on an unfired case without excessive bolt torque, so essentially zero headspace. This includes my 300WM which now headspaces off the shoulder rather than the belt. Brass has been very stable and I have barely any case growth on my 22BR brass or my 300WM brass, both having about 4-5 firings. The only exception to my zero headspace setup is semi-auto's which get an actual FL sizing and typically need trimmed every 2-3 firings due to case growth.
 

Veteran

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I was thinking what Tiny Tim was saying is if the die is over sizing and bumping the neck down a whole lot more than it should be, then a lot of brass gets pushed down in the case body flowing until it can't go past the belt. Then when the case gets fired, it elongates again everywhere including from the belt forward and from the shoulder forward. That repetitive pushing down the brass into the belt, and then firing and stretching it back out at the belt where it got pushed to is what causes fatique wear on the metal, and that's why the case separates just above the belt. If that ain't what he meant, then I dunno either. But, I think its possible. My sense is that if I am gonna full length size, belted magnums, I have to do a better job of measuring and understanding how much I'm sizing them and where that sizing is occuring in the case.

If the consensus here is that if I bump the shoulder back about .002 that this will solve the problem, I'm gonna try that.
I'm also gonna know if I have actually been over sizing and pushing too much metal down on that belt each time, either way--
cause I'm gonna start measuring things a lot more precisely vs. just trusting RCBS said turn the die this many turns, and all will be well!
Cause that sure did not work! Pulling broken shell casings like hotcakes outta breeches makes me think reloading is dangerous!
.300 win mag or .338 LM ain't supposed to to be shooting cases in little pieces and parts back to the rear..........
 

Tiny Tim

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I was thinking what Tiny Tim was saying is if the die is over sizing and bumping the neck down a whole lot more than it should be, then a lot of brass gets pushed down in the case body flowing until it can't go past the belt. Then when the case gets fired, it elongates again everywhere including from the belt forward and from the shoulder forward. That repetitive pushing down the brass into the belt, and then firing and stretching it back out at the belt where it got pushed to is what causes fatique wear on the metal, and that's why the case separates just above the belt. If that ain't what he meant, then I dunno either. But, I think its possible. My sense is that if I am gonna full length size, belted magnums, I have to do a better job of measuring and understanding how much I'm sizing them and where that sizing is occuring in the case.

If the consensus here is that if I bump the shoulder back about .002 that this will solve the problem, I'm gonna try that.
I'm also gonna know if I have actually been over sizing and pushing too much metal down on that belt each time, either way--
cause I'm gonna start measuring things a lot more precisely vs. just trusting RCBS said turn the die this many turns, and all will be well!
Cause that sure did not work! Pulling broken shell casings like hotcakes outta breeches makes me think reloading is dangerous!
.300 win mag or .338 LM ain't supposed to to be shooting cases in little pieces and parts back to the rear..........
You could measure a fired case with a comparator, FL size it as in the past and measure it. The difference would be how much you're moving the shoulder. You might also be able to compare a factory loaded round to one you resized. It may help understand what is going on.
 

Tiny Tim

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How would that stretch at the head? If belt to bolt face were in spec, this area moves about 0.001”. If the shoulder is oversized, it blows forward. Hmmm…
If the shoulder is completely unsupported (unlike an AI chamber where the neck shoulder junction it creating your headspace), the case will stretch along its entire length, not just push the shoulder back into place. I agree, it could be a headspace issue, and the OP could have that checked relatively inexpensively.
 

Veteran

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You could measure a fired case with a comparator, FL size it as in the past and measure it. The difference would be how much you're moving the shoulder. You might also be able to compare a factory loaded round to one you resized. It may help understand what is going on.
agree.
 

Veteran

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If the shoulder is completely unsupported (unlike an AI chamber where the neck shoulder junction it creating your headspace), the case will stretch along its entire length, not just push the shoulder back into place. I agree, it could be a headspace issue, and the OP could have that checked relatively inexpensively.
How is the best way to measure head space on a belted cartridge in a breach loader?
 
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