Bent Case Necks

[rwdwrt]

I have some brass (Lapua) when I first got it it was great, fired it once then neck sized it with and RCBS neck die. Afterwards the neck seems to out of align. Didnt notice till chambering some rounds. There have even been some loads where, when chambering the shell chambers hard and also extracts hard (non fired) after ejection upon examination the bullet has been scratched on one side. I can put the round in a wilson case length guage and it looks off center at the bullet end. Tried Full length resizing the same cases and the problem seems to go away. Its as of the neck sizing die bends the necks. The bend is noticeable when trimming the case on a Redding Trimmer with the pilot insert. Even after Full length sizing to try and get rid of the bend, there still seems to be a slight bend but not as bad, as the bullet dosent seem to scrape against the side anymore .

Anyone have any experinece with this, or opinions on the issue?? Thanks

 

[snuffy]

caliber?

Is it a caliber specific neck die, or one of the "universal" dies? I HAD a Hornady universal die that would do that. It's gathering dust somewhere in the loading room.

What brand press? May be a ram alignment issue, or the shell holder is not all the way into the slot.

 

[rwdwrt]

The Press is a C&H, probably 30 yrs old, has twin steel guides like an arbor press. The sheel holder is a RCBS, the one where different calibers can interchange by snapping in and out. The is specific to 308. As I said I only started to notice the problem when I started neck sizing, but it could have been there before

I am considering new Forster Dies and a new press if I cant get things to straighten up.

 

[ranger335v]

Your bent necks are the result of stretching them while pulling them over a small "ball" type expander after sizing. Changing to another brand of conventional dies or press or shell holders will prevent it.

Lubing the insides of the necks with case lube will usually help but will not prevent it.

Get a Lee Collet Neck Sizer Die. It does not distort necks while sizing and it does not require lubing.

Next best thing are Forster BR dies. They have a height adjustable expander ball that can be moved up the decap rod far enough to begin expanding as soon as the neck begins to move down. That helps maintain straight necks but not as well as the Lee Collet does.

 

[USSR]

Your bent necks are the result of stretching them while pulling them over a small "ball" type expander after sizing.

That's why I don't use an expander in my dies.

Don

 

[moosehunt]

I have to disagree regarding the expander being the culprit. Without getting into it regarding the pluses and minuses of expanders vs non-expander loading, the expander, when being pulled out of the neck pulls straight out. It may cause stretching and it may work the brass excesively, but it won't cause bending or crooked necks because it pulls straight out, not at an angle or cant. I suggest you check the cases on a comparitor before sizing to verify if they are straight at that point. I'm betting they aren't. If there are variations in the brass thickness of the case body, then the brass will take on a slight banana bend upon firing. This is a lot more common than many realize. Usually it isn't seen without a comparitor. Have you had this problem before? Is this different brass? Is this a different sizing die? The expander isn't the bad guy in this. It's more likely the brass.

 

[rcmodel]

Well, I kind of lean toward the expander button myself.
The crooked case almost has to be straightened when it runs up in the sizer die.

But, for the same reasons you outlined, if the case neck is slightly thicker on one side, the expander will do it's thing more on the thin side of the neck coming back out, and a crooked neck will result.

If there is a dry case neck and a lot of drag & squeeling, it will really result!
I think cleaning & lubing the inside case neck before sizing will help, if not cure his problem.

rcmodel

 

[ranger335v]

My concentricity gage says it's the expander ball, your milage may vary.

Soft or thin places in the neck will surely stetch, or "bend", more than the rest of the neck. The carbide expander balls that Hornady used to market were helpful by reducing the neck stress but they are hard to find now, don't think they make them any more.

I use a universal decapper and Lyman "M" expanders for all my precision loading, just to avoid conventional expanders. The "M"s are significantly better in maintaining straighter necks (for me) and have the added advantage of assisting in straighter bullet seating in my Forster seaters.

 

[Wildfire]

??????

Hey there:
With out seeing the problem we are all guessing. while I agree with all of the others, you could have a bent decapping rod also.
I clean out my die's a lot more often now and polish that expander ball once in a while.

 

[rwdwrt]

Loads of good info here guys, Thanks
I have been checking everything out that has been mentioned.
The cases that were bent, I ran them through an old FL die (RCBS) and loaded some dummy rounds into them, they chamber fine with no hard bolt.
I have examined the decape pins on both dies and the one on the neck die that was seemingly bending them gives off the illusion that it maybe bent slightly, I have no gauge to measure it though, just rolling it across flat surface and between my fingers. The best teller of it being bent or off center slightly though is when it is installed in the die, look down into the die and turn it, you can see it moving slightly from center to side. This may be the culprit. Think i may try the rubber o-ring idea just to see what happens. It seems to let the pin and expander ball give a little, kind of like floating in the die.

IMHO , I wonder why they make the expanding balls the shapes that they do seems like a nice tapered that would gradually expand the neck out would be best.
Also the design of the Forster die, with its expander ball high in the die makes a whole lot more since than the usual placement in other dies.

Anyway got my cases back to usable with th FL die, I will probably be odering a new neck die with a different design to avoid this problem in the future.

 

[moosehunt]

rc--I'm referring to the case body walls. If one side is thinner (or better, regarding the glass being half full--thicker) then at firing, the expansion will be greater on the thin side. The elasticity aspect will hense "spring" the thin side back to a lesser degree. Then, when going into the FL sizer, same thing regarding elasticity--the two varying sides don't respond the same. The result is a banana shaped case--AFTER the FL die. Not at a degree that is obvious, but significant enough that when extrapolated out through the neck and bullet, significant runout! Check a bunch of cases and you'll maybeso be surprised at how often it occurs. Through in a batch of less than perfect brass--I don't care the manufacturer, it happens--and you can have some major effects that often are not noticed--except on the target.

 

[Wildfire]

Bent Rod.

Hey there:
I'll stick with the bent decapping rod.

 

[rcmodel]

Seems to me if the decapping rod were bent that far, you'd bust the decapping pin on the first case!

No way it would line up with a flash hole.

rcmodel

 

[Eagle103]

Have you used this die before without any problems? If so the die could be dirty in the shoulder area or the expander ball is way off.

 

[David Wile]

Hey rwdwrt,

You did not mention if you were crimping your rounds. If you are crimping, you might check to see if the crimping process is causing a deformation.

As far as the expander ball goes, I have used expander balls in sizer dies with success for over forty years. I do find, however, expanding the neck works with ease if each case neck is rammed with a wire bore brush dipped in a little lube. That gets rid of dirt from the inside of the neck and puts enough lube on the inside to make the expander slide easily and still not harm the powder charge.

I have seen some folks use a Lee Crimp Die so hard that it can deform the case at the shoulder.

Best wishes,
Dave Wile

 

[Wildfire]

You may be right

Hey There:RC may be right , I do it a little different. I deprime, Clean, remove the decap pin and then size. I use a different expander ball at that point.This is only for my serious target guns. I know it is an extra step, but when loading for those rifles I don't care how long it takes.Cleaning the dies is a must and I assumed that was being done.I only run cleaned brass thru the dies, and always lube the inside of the case necks when sizing. I never crimp rifle rounds .* A crimp could deform the shoulder.