Case neck mouth belling problem

[shaun1826]

I’m getting some case neck mouth bell when using an expander mandrel. Do other people have this issue when using a mandrel? This is 223 Lapua brass that has been 1x fired (fireformed to 223 AI). I used the same mandrel on the virgin brass and didn’t have a problem. After full length sizing I‘m using an expander mandrel (dipped in emperial dry graphite lube) at which point the case mouth is “belling“ out to 0.252 wheras the rest of the neck is 0.249. I checked a case after full length sizing and the bell is not there. It is definitely occurring after using the mandrel. After seating a bullet this bell won’t allow the round to chamber. The chamber is 0.253. Any help would be appreciated.

 

[918v]

Did you check the diameter of the mandrel from beginning to end?

 

[Holliday]

You have enough clearance in your die so that the neck is not bottoming out on the mandrel shoulder?

 

[iceng]

As max said. Probably need to back it off slightly

 

[samb300]

I had this same issue when I tested the dry graphite lube. Imperial lube or maybe even One Shot should help; I use Imperial on a qtip to swab the neck ID. As others have mentioned, also make sure you’re not bottoming the case out on the tool.

 

[briang7511]

i have done the same as samb, with a q-tip and some case lube spray. also need to clean the mandrel often, i noticed some build up of the corn cob media dust after a few hundred sticking to the oil. just need to get the top edge and one q-tip can do at least 30 pcs before re applying some lube to the q-tip.

 

[ditter]

i get the same thing on my 6.5CM, with a sinclair madrel. Annoying as hell. I backed off the die a bit and it has helped. Luckily, mine was always able to chamber. But it wouldnt go back into an ammo checker. Going to try the One shot.

 

[shaun1826]

I just double checked and the case is not bottoming out in the mandrel die. The mandrel is going deeper than the neck depth. It’s going about 0.30 past the taper part on the mandrel whereas the neck depth is about 0.19. The mandrel measures 0.2230 inch the entire length.

 

[918v]

Is the bell consistent around the case mouth? Possibly misaligned case with mandrel.

 

[427Cobra]

Your neck is being sized too small, as the expander mandrel is being inserted the brass has to go somewhere so a bell happens, try using a bigger bushing in your die, one that barely allows the expander ball to touch on the way out, then the mandrel

 

[Holliday]

I remove my expander ball completely. But I use a bushing die that sizes down so the mandrel just opens it a bit.

 

[Rocketmandb]

Your neck is being sized too small, as the expander mandrel is being inserted the brass has to go somewhere so a bell happens, try using a bigger bushing in your die, one that barely allows the expander ball to touch on the way out, then the mandrel

When using an expander mandrel, using a right-sized bushing is important for a couple of other reasons too:

- You work the brass less
- You get more consistent springback, and thus tension

 

[shaun1826]

I’m using a Lee full length sizing die (no bushing or expander ball). I know, Lee is not liked by many, but it was all I could get in 223 AI full length sizer at the time. A fired case has a neck diam. of 0.252 (0.253 chamber). The sizer die sizes the neck down to 0.2415. I just resized 3 couple cases to confirm the neck sizing and realized I was wrong, a small bell is happening at the mouth during rezing. The case mouth measures 0.243 whereas the rest of the neck is 0.2415. I’m not sure why any bell is occurring during resizing and no, the case mouth is not hitting anything inside the die as I was able to visually confirm.

This time I then used hornday one shot on a qtip to swab the inside of the 3 cases before mandreling. Low and behold the bell pretty much went away. The mouth now measures 0.2490 after using the mandrel and the rest of the neck is 0.2485. So, I think using Hornady 1 shot inside the case mouth has fixed my problem. The case mouth using imperial dry lube on the mandrel was .251 and with one shot is 0.249.

I guess the question now is, is the Lee die sizing the neck too much to be acceptable at 0.2415? I guess the ideal resizing would put the neck at 0.247 or thereabouts so that the mandrel is only opening the neck up 0.002 instead of the 0.0075 it is now.

 

[918v]

The bell happening during resizing is normal. That’s why Lee pushes their collet crimp die. It removes the bell. Also, if you adjust the seater die carefully, it will remove the bell during seating.

 

[Dolomite_Supafly]

Do you tumble with pins? I have witnessed myself and well as told by a bunch of others that tumbling with pins can mushroom the case mouth enough to cause problems in tightish chambers.

 

[shaun1826]

Do you tumble with pins? I have witnessed myself and well as told by a bunch of others that tumbling with pins can mushroom the case mouth enough to cause problems in tightish chambers.

I wet tumble but do not use pins.