Loss of neck tension (10mm)

[ATLDave]

Suddenly my 10mm brass has insufficient neck tension. After resizing (i.e., before use of the expander die), the bullet can sometimes even be seated by hand, with no use of the press required! Obviously, setback happens too easily, so I've disassembled all the rounds exhibiting this characteristic. I'm using PPU-marked brass that's been fired at least once, and probably 2-3 times before, all at loads well below book max and with no exhibition of pressure signs.

I measured the bullets (Montana Gold JPH's), and they are right at .400; some Berry's that I had were just a touch larger on average, but I got the same neck-tension problems with them, so I don't think it's an undersize batch of bullets.

Any idea what's causing this? Has the mouth of the case been work-hardened so that it's springing back despite the resizing die? Has the brass gotten too thin (I haven't trimmed); PPU seems to be a touch thinner on average than the Starline that I use for stronger loads. Can resizing dies go out-of-spec or get loosened in some way after about 1000 rounds? Any suggestions are appreciated.

 

[NeuseRvrRat]

if other brands of brass are reloading with sufficient neck tension, then i'd say it's probably thin brass. i've had problems with R-P brass in straight-wall pistol cartridges because it's so thin.

 

[Certaindeaf]

Maybe your sizer die is out of spec or on the large side.

 

[GLOOB]

Has the mouth of the case been work-hardened so that it's springing back despite the resizing die? Has the brass gotten too thin (I haven't trimmed)

Combination of the above. Over time, your thinner cases will no longer get the right tension. The older they get, the worse the problem. Also, the bigger your chamber at the case mouth, the worse this problem will be.

If this is happening to a lot of your brass, you might consider trying a new sizing die.

If it's a smaller problem, what I do is to cull brass that expands/flares too easy. But of course, that would not work so good if you use a progressive press. For relatively expensive/rare 10mm cases, I might even experiment with annealing.

 

[tightgroup tiger]

If it were me, I'd back my neck sizing die off until it starts either shaving brass or lead, or I can't get the bullet to start at all no matter what.
Then bring it back down until you can just get it to sit on top of the brass and seat without shaving, and go from there before I'd throw away the brass.

The best neck tension you can get will come from doing this. If the neck sizing die is adjusted down to low it will undo everything the resizing die just did.

I find with my 9mms that the more I shoot and resize them the tighter the neck tension gets because I run my neck sizer at the bare minumum I can set it at, to still get a bullet to start without shaving lead or brass, even if I have to mess with it a little to get it to stay put before I run it into the bullet seating die.

I also won't use any brass that is out of the Sammi specs for case length. The longer ones I trim, the ones that are shorter than Sammi specs I pitch. I've found out over the years that the dies can't be adjusted to work with much more than .010"+or-. My life got a whole lot easier after I started doing this.
I use a LNL-AP and load 500-1000 at a time and don't have any problems since I started following this proceedure.

Now I know .40 are straight and 9s are tapered but the dies work the same. I would have no explaination as to why this started happening to you if everything was fine before the problem started. I do know that I had a mysterious problem start with my 9mms and I think I problably set my neck sizing die up with a shorter case and the longer ones happened to get the necks resized to deeply because of it. That's what brought me to start the proceedure I described above and since I've had, if anything, to much neck tension which is easy to deal with compared to the other way around. My biggest problem now is watching for split necks which is easy to feel when seating the bullet.

It may be you got ahold of a short case when you set your neck sizing die and your cases are growing in length from the resizing process, so now the neck sizing die is going to deep into the case making your bullets loose.

 

[Certaindeaf]

I think you mean the flaring die. He also says that a bullet will slip into a fully sized and unflared case.

 

[rcmodel]

Can resizing dies go out-of-spec or get loosened in some way after about 1000 rounds?

Check the sizing die for a cracked or missing carbide ring insert.

But chances are about 100% the PPU cases are too thin to start with.

rc

 

[tightgroup tiger]

He also says that a bullet will slip into a fully sized and unflared case

I must have missed that. That's a little strange unless, like RC said, something is wrong with his resizing die or the brass thickness.
That's really strange if he has the resizing die touching his shell holder like it is supposed to be.

 

[gamestalker]

Take a look at the inside of the sizer die to see if the carbide ring has fractured, happened to me with a 9mm Lee carbide die. You should be able to either feel the fracture or see it, and it may leave a vertical line down the body of the brass. When resizing with most carbide dies, it is recomended to not adjust the sizer die down to the extent it makes contact with the shell plate, as this causes the ring to fracture. The carbide ring is very hard, but also very brittle.

GS

 

[ATLDave]

I must have missed that. That's a little strange unless, like RC said, something is wrong with his resizing die or the brass thickness.
That's really strange if he has the resizing die touching his shell holder like it is supposed to be.

Oh, yeah, the die definitely touches the shellholder at the end of the stroke. It's set up (externally, anyway) exactly as it has been for hundreds or thousands of previous (problem-free) loadings.

 

[ATLDave]

Take a look at the inside of the sizer die to see if the carbide ring has fractured, happened to me with a 9mm Lee carbide die. You should be able to either feel the fracture or see it, and it may leave a vertical line down the body of the brass. When resizing with most carbide dies, it is recomended to not adjust the sizer die down to the extent it makes contact with the shell plate, as this causes the ring to fracture. The carbide ring is very hard, but also very brittle.

Interesting, and something I had not considered. I will check that tonight.

 

[gamestalker]

ATLDave,
I think you may have mis-understood what I was saying. What I am saying is that some carbide dies are not supposed to make contact with the shell holder at all. Lee is one of those that shouldn't, stating that it can fracture the carbide ring. I think RCBS is also one that isn't supposed to contact the shell holder. Ever since my 9mm carbide ring broke, I have taken great care to make sure I at least have minimal clearance off the shell holder.

If as you said, the die has worked fine for hundreds of reloadings, and now it isn't, it can only be that the carbide ring has fractured or has fallen out.

GS

 

[tightgroup tiger]

I have only used Lee and RCBS carbide dies for all my handgun loads but I use progressive presses and I do set my dies to just barely touch at top of the stroke but I rely on the normal amount of deflection in the shell plate to give me that clearance as to not damage my dies. It's only a couple thousands of an inch but it's all that's needed.

If the OP is using a single stage, yeah, that could damage a die. I never preload any of my dies though.

 

[Taterhead]

Some dies are on the larger side of the specs, and some brass is thinner. The combination of the two can cause the brass inside diameter to be over-sized after running up into the re-sizer.

Good advice from above about checking your die. Do you have any other brands of brass to compare to? If the PPU brass worked before, but does not now, you are probably a bit work hardened and time to toss. That would also lead me to believe that your die is a bit on the larger side of specs. My gut feeling is brass is the culprit though and time to toss. I have had 10mm nickel cases that get hardened after 4-5 rounds and lose neck tension noticeably.

What is the outside diameter of a resized case? My 10mm RCBS die is a bit narrower than some so I get pretty positive neck tension. The only exception being the nickel cases that I mentioned earlier.

Good luck!

Edit: To expand on the point about RCBS dies above, they do call for them to NOT touch the shell holder in order to avoid damage to the die. With my rifle dies I screw them down all the way so that they "cam over," but carbide dies are turned out to barely miss the shell holder.

 

[ATLDave]

Well, I think I know the answer now. A new batch of Starline brass solved the issue 100%. Brass is tight enough to see the outline of the bullet through the brass. Resizing die is still tight around new brass. It was the old brass being thin and/or hardened to the point of losing its springiness.

Thanks greatly for all the ideas and suggestions fellas!

 

[Certaindeaf]

Huh, that's believable. Usually the necks crack or primer pockets enlarge first. How many times did you load that brass? I remember back in my crazy young days a good 9mm case would last me one or two loadings before it wouldn't hold a primer any longer! lolz

 

[ATLDave]

The brass had probably been fired 3, maybe 4 times. Once as a factory loaded round, then 2-3 reloads. Only one split/cracked case. Brass "looked" ok, just wouldn't hold tension after sizing. Primer pockets still seemed as tight as ever.

There were no visible indications of a problem prior to bullets being loaded. After loading, lack of a bullet outline was a hint. Slight snugness in my Wilson case gauge was another. And, of course, the ability to set back the bullet by hand.