Case mouth belling after FL sizing

[rockhound78]

I have had that happen sizing 308 brass. As Dusty said, I think your die is sizing the brass down more than it needs to. When you pull the expander ball out, since there isn't any brass after the case mouth, the radial stresses at the mouth cause to to flare a bit.

Do you notice a greater force needed to finish the sizing process. Measure the case neck dia on a sized case, midpoint on the neck, and do the same, but take out the expander ball and let us know the difference. On my 308 die, the difference was on the order of 0.010". I went to a bushing die.

 

[DiRTY DOG]

Another question. When you use the expander assembly what size is your finished neck diameter versus without it? The relationship between how much the die makes your neck and the expander makes it is too severe.

Expander button - 0.2630"

Inside neck diameter:

• 0.2620" - Fired
• 0.2600" - FL sized with expander
• 0.2550" - FL sized no expander

Outside neck diameter:

• 0.2940" - Fired
• 0.2880" - FL sized with expander
• 0.2850" - FL sized no expander

0.2900" - Loaded with 123gr Scenar
0.2915" - Flared mouth lip after FL w/expander and seated 123gr Scenar

(measurements at mid-neck)

 

[Coyotefurharvester]

Does the flare occur if you run the other tip with the expander(no decap pin) ? Only the manufacturer will know if the expander/rod is out of tolerance(length).

 

[6MMsteve]

put a heavy outside chamfer on the brass maybe, new brass sometimes has a burr on the outside mouth when you FL size the burr gets pushed in, then when the expander comes into play it will bell the brass, I had this and just used a heavy outside chamfer but I could be wrong also, but since I have started the heavy outside chamfer I have no more belled cases..then again I can be wrong, won't be the tenth time

 

[22BRGUY]

Do you measure case length before resizing?

 

[Bill K]

If that deprime/sizing rod is a fixed one, then I would say your cartridge length is every so longer than necessary. Check cartridge length and trim if necessary and see if that does not stop it.

And your could camfer the case mouth prior to seating a bullet.

 

[DiRTY DOG]

If that deprime/sizing rod is a fixed one, then I would say your cartridge length is every so longer than necessary. Check cartridge length and trim if necessary and see if that does not stop it.

And your could camfer the case mouth prior to seating a bullet.

COAL is under trim to length, the Lapua cases were all well under max brand new.

Chamfering does not get rid of the flaring. The lip is significant, about 0.0035".

 

[Bill K]

Then I would try raising your sizing die and maybe with the neck not going in so far, the bell would not occur.
Other wise I would check with the die maker and/or get another brand sizing die.

 

[22BRGUY]

Along the lines of what Bill K said, I would try to find out exactly where in the process
the flaring is happening.
I would start out by unscrewing the die about 1/2 turn and see if it still happens, Then if not,gradually turn the die back down a little at a time to try to determine where exactly
it begins to flare.
What kind of press do you have and have you reloaded before without the flaring happening?

 

[Dave M.]

Expander button - 0.2630"

Inside neck diameter:
0.2560" - Fired
0.2600" - FL sized with expander
0.2550" - FL sized no expander

Outside neck diameter:
0.2940" - Fired
0.2880" - FL sized with expander
0.2850" - FL sized no expander

0.2900" - Loaded with 123gr Scenar
0.2915" - Flared mouth lip after FL w/expander

(measurements at mid-neck)

That’s quite a bit to size the neck down. I don’t think it has anything to do with your issue, just an observation.

 

[243winxb]

https://forum.accurateshooter.com/threads/case-mouth-doughnut.3983036/page-2

 

[DiRTY DOG]

Does the flare occur if you run the other tip with the expander(no decap pin) ? Only the manufacturer will know if the expander/rod is out of tolerance(length).

https://forum.accurateshooter.com/threads/case-mouth-doughnut.3983036/page-2

The flaring happens with ZERO wet/dry tumbling.

• Fired cases extract with straight necks no flaring.
• FL sizing without the expander results in straight necks no flaring.
• FL sizing with the expander results in a flared mouth.

All with ZERO tumbling. So... It must be related to the expander, right?

 

[nmkid]

put a heavy outside chamfer on the brass maybe, new brass sometimes has a burr on the outside mouth when you FL size the burr gets pushed in, then when the expander comes into play it will bell the brass, I had this and just used a heavy outside chamfer but I could be wrong also, but since I have started the heavy outside chamfer I have no more belled cases..then again I can be wrong, won't be the tenth time

That's what I have done with no problems.

 

[DiRTY DOG]

I ordered a honed Forster die to try instead.

 

[22BRGUY]

Am I reading your numbers right? That the fired case inside neck diameter drops
in size .0040 upon firing?

 

[243winxb]

Case neck wall thickness needs checked.
Size a fired case, no expander, NO neck lube. Seat a boatail* bullet. Measure outside diameter of mouth edge, middle of neck & close to shoulder.

There may be more brass near the mouth, thicker. Standard dies can move brass in the neck area, when sizing. More so when annealed & on the soft side.

Outside neck turning & bushing dies may help?

 

[6MMsteve]

That's what I have done with no problems.

yes I put a heavy inside and out, it's sharp but I don't have that issue nomo, plus some cases have extra material in that area like it's rolled, and I was having some issues with material displacement uneven nks when I ran the ball mic, and erratic shots and I took a bunch of cases to the lab at work and kinda dug in and come up with simply making a heavy chamfer. I run no turn nks

 

[6MMsteve]

there is excess material at the mouth on the outside on some of the cases, use a magnifying glass and light and it can be seen. it could be the lot of brass sometimes they're great sometimes not, Lapua peterson any of them, I discovered this yrs ago, but what do I know, to chk brass good you need about 30 points of measure starting at the mouth and work down, very time consuming, I just purchased some peterson brass that was once fired and some 2x fired a small raised ring was at the top outside of a lot of cases

 

[DirtySteve]

Try backing your die off one full revolution and see if it still happens..

 

[DiRTY DOG]

Am I reading your numbers right? That the fired case inside neck diameter drops
in size .0040 upon firing?

Sorry, typo. Corrected above.