Got a bulge...

[L.Sherm]

Ive seen it before. What is the neck diameter of a fired case and a sized case? Seen this before. not a reamer issue.
Mike is correct. IME the neck rises above the bushing while the lower neck is being sized and brass flows forward and expands the unsupported rim of the neck.
I should add, it happens in standard FL dies also when end of neck rises above the neck sizing area of the die

I could see that happening on the down stroke but what about on the up stroke? It has to come back through the bushing.
Same thing on a non bushing has to come back through the neck.

 

[L.Sherm]

Is the pic of a piece of fired brass or after sizing?

 

[Jeff Heeg osoh]

If its not ground properly!!
The very end of the neck is bigger than the rest.
Most saami reamers are ground with some taper in the neck.

if as you say the reamer was not ground correctly and as shown in the picture at the very end of the neck is larger in diameter. Well if thats the case with the reamer the whole length of the neck would have to be the larger diameter. Its drilling a hole and if the fat end goes in first the complet hole will be fat if that helps for some to understand.

osoh

 

[P7M13]

1. Need to know the web thickness of the neck along its axis.
2. Try using a different die, or one or two mil larger diameter bushing. You can prolly get customs made by CH4 or others.
3. Get one of those new-fangled Lee neck sizer dies [/sarcasm]

In my recent brass reforming experience, while I really like Peterson Cartridge brass, it is notably softer than Lapua or Norma brass. Hence, it would work-flow more easily during resizing, as is suggested above.

 

[nksmfamjp]

How are you expanding necks?

Also, are you annealing? If so, when? If not, how many loads on the brass?

 

[L.Sherm]

One would think that a case like that would have some extraction issues if its a fired case.

 

[Jeff Heeg osoh]

Some may be over thinking this in regards to the effect in accuracy. The measurement that would be interesting to see is after a bullet has been seated, the flared end now may be equal.

one question to the op, mainly a safety question you are trimming overall length on your cases to eliminate any chance of deadheading the case neck relief in the chamber when fired and case expansion takes place?

osoh

 

[Phil Rizzo]

I've seen excessive pressure from the chamfer tool cause belling.
doesn't take much to cause it behind a fresh annealing. Just a thought

 

[The Oregonian]

If you are cleaning with SS media it could be peening the necks…I stopped using SS media for that reason.

 

[Jasbo]

But it's not where I thought folks talk about.View attachment 497861
When I hear about bulging necks, I had thought it was at the neck/shoulder junction, not the case mouth. I trim every shot, with a 3 angle RCBS trimmer. I anneal every shot. I deburr with a VLD type tool, Lyman. Every shot. In the process of acquiring pin gauges.
33XC cartridge. Peterson brass. Tubb dies, with a neck bushing, currently running a .363 bushing.
Can somebody tell me how this forms, and how to stop it? It can not possibly be helping me !

The photo I see is of a buttstock! Don't find a photo of brass.

 

[Gregg C]

I agree on looking at the chamber, looks to me like you got brass flowing to the end of the neck if this is a fired case.
If it is I would be looking at the reamer as the culprit.

It's been sized. Fired cases are more square, although with the tools I currently have, I cant tell if they are straight. I think there is still a small ridge there.

 

[Gregg C]

Ive seen it before. What is the neck diameter of a fired case and a sized case? Seen this before. not a reamer issue.
Mike is correct. IME the neck rises above the bushing while the lower neck is being sized and brass flows forward and expands the unsupported rim of the neck.
I should add, it happens in standard FL dies also when end of neck rises above the neck sizing area of the die

Fired is .376.
Sized is .363
Bullet seated is .367
Neck is .0144 to .0146

 

[Gregg C]

Ive seen it before. What is the neck diameter of a fired case and a sized case? Seen this before. not a reamer issue.
Mike is correct. IME the neck rises above the bushing while the lower neck is being sized and brass flows forward and expands the unsupported rim of the neck.
I should add, it happens in standard FL dies also when end of neck rises above the neck sizing area of the die

Tubb makes this die. The neck doesnt come above the bushing, still below top of bushing by .100+

 

[Gregg C]

The photo I see is of a buttstock! Don't find a photo of brass.

Does look kinda like a butt stock, don't it?