Neck Sizing Vs. Full Length Sizing and Neck Tension

Veteran

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Ok, I don't want to start a food fight or anything, but I am curious what everyone on this forum has to say about this subject. I've seen the Erik Cortina video where he says neck sizing is just passe and so much old lore, and to just full length size for consistency. I've seen some other videos on youtube which sort of cite him and say they agree. However, in my own experience, I haven't so much run the tests to match up one method against another, its just that I learned the hard way you CANNOT full length size belted magnum cartridges past 2-3 times without head case failures. At least I could not. I had 6-7 head case failures on my .300 win mag. which of course is a belted magnum. I even had one lower half stay in the chamber so tight, I had to fill it with earplugs, then fill with an epoxy, and then ram it out from the barrell end.......not fun. So, now I neck size all my new Peterson Brass and have had no more issues or failures and I'm up to 5 times on that brass. Full length sizing at least with my RCBS dies just overworked the brass shoving it back down on the belt, and then the firing would stretch it back out until it failed above the belt in case head separation due to metal fatigue. No one ever told me not to Full length size belted cartridges, no book, no article, nobody told me. I had to learn the hard way.

But, I do full length size my .338 Lapua Magnum brass every 2-4 firings now, and neck size it the rest of the time, just to try to get a little more life out of it. I think just anecdotally I see better group sizes on it when I neck size it. I haven't run any real tests yet. Is there any real scientifically consistent and valid data run by anyone you can point me to who has done exhaustive testing on this subject as to group size vs. method?

Next, I've seen some videos by sdkweber and bolt action reloading on youtube where they ran some tests that seemed to indicate that either 2 thousands or 3 thousands neck tension is optimum for shooting small groups. Is there an accepted standard in the community and if so what is it, and can you again point me to any definitive studies that are scientific, exhaustive, and consistently run that says what the answer is?
One guy says 2 thousands works best, and another seemed to end up with a relationship what shows 1 thousands is worst, 2 thousands is better and 3 thousands is best in a curvelinear line that shows diminished gains at the 3 thousands mark, ie not much to be gained if any past that.
Does anyone have a magic wand or a crystal ball?

I'm just digging in and trying to get it right!
 

AZ-SHOOTER

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Jun 4, 2021
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AZ/NM
I bump everything .002-003" at the shoulder with no issues and pockets wearing out first most of the time. Anneal every other firing and run .003" neck tension on everything. Works great for me and I am able to maintain low teens to single digit es/sd.
Tried the neck only thing was a pain to FL size every 4 or 5 firings wasnt getting any better results that I could tell. I try and keep things simple as possible. I used to be real particular about loading and all the "peace of mind things" but nowadays if i cant truly notice if it helps I dont do it.
 

Tiny Tim

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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.
 

Veteran

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Well, I must say bumping the shoulder back a little to make the belt seat better so there is not excess head space left over after the cartridge elongates after firing makes some sense to me. I am sure willing to try that. It's just a step further than I have gotten in my reloading. Are there specific dies anyone recommends that are easy to set up for FL sizing with a shoulder bump that works well?
I'm not sure that my standard RCBS dies will set up to do a shoulder bump unless its just a matter of experimenting with the distance the cartridge gets pushed up into them? Let me know what you recommend to do this. I plan to try it. I can also see that annealing with this working the shoulder is gonna be more important. Thanks for your help.
 

Tiny Tim

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Well, I must say bumping the shoulder back a little to make the belt seat better so there is not excess head space left over after the cartridge elongates after firing makes some sense to me. I am sure willing to try that. It's just a step further than I have gotten in my reloading. Are there specific dies anyone recommends that are easy to set up for FL sizing with a shoulder bump that works well?
I'm not sure that my standard RCBS dies will set up to do a shoulder bump unless its just a matter of experimenting with the distance the cartridge gets pushed up into them? Let me know what you recommend to do this. I plan to try it. I can also see that annealing with this working the shoulder is gonna be more important. Thanks for your help.


Just back your standard fl die a half turn or so. Then adjust down til you get the desired "bump". Alex Wheeler has a great video on this with a stripped bolt assembly (I think. It might be for finding the lands. I don't recall.)
 

okie man

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Dec 21, 2013
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Proper full length sizing is easier and more failsafe than neck sizing only. A few measuring tools and Redding competition Shell holders are all you need. Some companies will even hone a die for your gun. Send a handful of fired cases from your gun, your dies and shell holder and you'll get a matching set back. Jmho though
 

deweyduck

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Jun 27, 2013
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Well, I must say bumping the shoulder back a little to make the belt seat better so there is not excess head space left over after the cartridge elongates after firing makes some sense to me. I am sure willing to try that. It's just a step further than I have gotten in my reloading. Are there specific dies anyone recommends that are easy to set up for FL sizing with a shoulder bump that works well?
I'm not sure that my standard RCBS dies will set up to do a shoulder bump unless its just a matter of experimenting with the distance the cartridge gets pushed up into them? Let me know what you recommend to do this. I plan to try it. I can also see that annealing with this working the shoulder is gonna be more important. Thanks for your help.
I use RCBS too and all you have to do is adjust the die seating depth in your press. Reread very carefully the set up directions in the brochure that comes with your die. Using the die locking ring makes it very consistent and it will repeat exactly every time except when case lube builds up in the die body. You must fully clean the body periodically to prevent drift in headspace. And the same applies to the bullet seating die plug as welI. I recheck my headspace and seating depth on every bullet that comes off the press to ensure that settings are correct.
 

Blacktailer

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Sep 17, 2019
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AZ
Just set up your die so the resized cases JUST chamber in your rifle. I never set a resize die without the rifle that the brass will be used in right at the reloading bench. As said above, back your resize die out about 2 turns and resize a case, then check it in your rifle's chamber. Does the bolt close easily? Probably not. So now turn the die down by 1/8 turn and repeat until the bolt will close easily. Now your die is set for your chamber with a minimum of brass working. I generally want to feel a little bit of resistance when the bolt closes but others want to feel no resistance, it is up to you. I also run every reload from the mag through the chamber before I go hunting.
I use mostly collet neck sizers just to not have to use lube unless the shoulders need to be bumped. Had a regular neck size die from a major manufacturer that induced .007 in run out in every case- I don't use regular necksizers anymore.
 

WapitiBob

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Oct 16, 2011
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Bend, Or
You can also back your fl sizer off a turn or so, then smoke the shoulder on a case (run the shoulder thru a wax candle flame), you'll see when it touches the soot when it gets adjusted down to the right spot. As mentioned a competition die set works well or you can use the larry willis collet to body size at the belt if you eventually have some bulging in front of the belt.
I just went thru firing number 6 on a batch of belted cases.
 
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