Excessive neck tension?


February 28, 2013, 02:20 AM
I have been having fits trying to seat bullets a little deeper in my 308, the neck tension is unreal trying to seat a bullet any deeper then 2.8" with several of my bullets and have even bent a few brass trying to seat them, when they do seat deep enough I am getting thin metal shavings off the bullets, I load for quite a few calibers and this is the first I have seen like this. All brass were FL resized on my RCBS die.
Couple questions, can this neck tension create excessive pressures or is that not a significant factor? Has anyone else had anything like this before, I thought it was just my SST bullets at first but I was loading up some experemental BT and TTSX loads for my range trip tomorrow and it does it with them too. Could this just be a defective die? I am new to 308 but not 30 caliber my 06 does not do anything like that and it is an RCBS too.

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February 28, 2013, 03:36 AM
The neck on a 308 case has ~ .002" of elastic deformation. Beyond that it is plastic deformation.

What does that mean?
The neck tension increases as the neck inside diameter gets down to .306". When it gets smaller than that, the neck tension does not increase any more.

Measure the inside of your case necks with pin gauges.
They are most likely MUCH smaller than .306" if you are using an out of the box full length sizer die.

But if you are using a Lee Collet neck die, you may have a ~ .306" inside diameter.

Some people use M dies to bell the mouth of the case for the bullets introduction.

February 28, 2013, 04:31 AM
I'm not familiar with those bullets as I've only just started loading and use Sierra. Are the boat tail or flat base? If flat base have you tried boat tail. Sounds like the mandril might be slightly undersized. If you can remove the mandril you may want to try measuring it with calipers. I don't know the specs for it but I'm sure someone here might or it could be found online. I would imagine from the previous post that it should be .305-.306 ish but that is only a guess. Good luck and keep us posted.

February 28, 2013, 04:39 AM
It sounds as though you have the crimp portion of the seating die making contact with the case mouth, in other words the seating die may be adjusted incorrectly.

With an empty case in the shell holder, thread the entire seating die in with the press ram fully extended until you feel the die make contact with the case mouth, then back the die out at least one full turn. Now when you go to seat a bullet, thread the seating stem, located at the very top of the die, up or down according to desired seating depth.


February 28, 2013, 06:43 AM
^^^ If you are trying to seat and crimp in the same step there is your problem. Most bullets will open up a case neck OK if it is not excessively small. If the neck is .002 smaller there should be no problem. With bullets that are not boat tail the case mouths should always be inside chamfered. I do not crimp any of my rifle rounds unless they are tube fed firearms. If you are trying to do both operations at once that can get you into trouble as well as not trimming all to the same length can if you are crimping. RCBS will provide a larger expanding button for free if you ask. Measure your expander button in your 06 dies and see if it is the same as the 308 dies it should be. Good luck.

February 28, 2013, 10:21 AM
Elastic deformation "bounces back" plastic deformation is bending that stays that way one all pressure is taken off of it. Sorry to all you engineers out there that is as best as I could explain it in under 50 words before I have had my coffee. I don't have any kind of crimp marks on the rim of the brass and as hard as I am pushing them I would think I would, tried seating a few of them with the 7mm-08 die just to be sure and the same results there.
Any thoughts on pressure, I did not work any of them up to max loads given the issues I am having, most I am doing is 2gr under using Varget, I would think these would be safe to shoot as long as I work them up as normal, but I could be wrong.
You have to pardon me, I have never and have no intention to crimp any brass, unless I get a big bore Safari magnum that is.

February 28, 2013, 10:32 AM
There is no such thing as too much bullet hold, I want all the bullet hold I can get, one more time, I can measure bullet hold, neck tension does not convert from tension to pounds of push, pounds of pull.

On my best days I can get an interference fit between the neck of the case and and bullet, no matter how hard I try nothing ever comes out as tension, to describe tension it is easier to start over by describing bullet hold, again, I am 'THE FANí of bullet hold, I want all the hold I can get.

F. Guffey

February 28, 2013, 10:40 AM
Then we can go back to Lyman (Ideal) in the mid 50s, The seating die does not have case body support, they suggested seating and crimping could defeat the purpose, they thought crimping anything but pistol ammo was a bad habit. They thought the slightest amount of excessive crimp caused the case below the crimp to bell, after that they thought the case would expand then fold, swell and bulge at the shoulder.

Again, the last time this subject was discussed it was decided the bullet did not slide of of the neck if the neck of the chamber allowed the neck to expand.

F. Guffey

February 28, 2013, 11:01 AM
So neck expansion under pressure prevents any excessive pressure from building up despite the fact that I have the bullets jammed in there? Now if I could just find a way to seat them a little deeper, my M70 308 is unlike my Savages, and Tikka, it appears to have a shorter throat and seems not to like bullets seated at max length. It put my Speers at 2.770 no problem, but I am bending brass trying to get the SSTs any shorter then 2.840" or BTs shorter then 2.790"

February 28, 2013, 11:15 AM

Just back your die out a little more away from your case holder and then lower your bullet seater stem a little. It is as mentioned above, your seater is trying to continue seating the bullet while the die is crimping the neck.


February 28, 2013, 11:43 AM
+1 on crimp.
Either intentional, or accidental, that is the only reason you can't seat them to any depth you desire.

And if the case mouth is shaving bullet jacket metal?
It would be good to chamfer the case mouths so they don't do that.


February 28, 2013, 12:46 PM
I agree the most likely culprit is in the crimping function (either accidental or intentional), but---from the description of what happens from the op, I wonder if the brass has been loaded (resized) enough times to have formed a "doughnut" at the neck/shoulder junction that is interfering with the bullet base?

February 28, 2013, 01:06 PM
...I wonder if the brass has been loaded (resized) enough times to have formed a "doughnut" at the neck/shoulder junction that is interfering with the bullet base?

Seeing as he is using boattail bullets, I don't see how.


February 28, 2013, 02:55 PM
Random idea from a new reloader here: If the cases were not trimmed and are too long would that cause or add to this problem? OP has this brass been trimmed or case length checked?

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