Carbon on necks and shoulder

[243winxb]

he removes expander from die for concentricity reasons and now the brass is coming out with not only carbon on the necks but down the shoulder

The neck/shoulder junction has a mini donut. The expander moves the brass to the OD , better sealing.

 

[Ledd Slinger]

I'm in agreement with Joe R here.

I've seen this same thing happen when the loaded round neck diameter is significantly smaller than the chamber neck diameter and brass is becoming work hardened. Have him measure a fired case neck diameter and a loaded round neck diameter to see the difference.

 

[rwj]

How would a lack of neck clearance lead to gas leaking past? Reason for asking is that I’m now starting to observe a small amount of carbon on some 6BR case shoulders and have discovered donuts at the neck/shoulder junction...

 

[rwj]

I’ve been annealing, will soon start neck uniforming which hopefully will make neck/shoulder carbon a memory for me too... thanks for the input!

Edit to add that I’m using a relatively low velocity/pressure node which may also be a contributor.

 

[243winxb]

Size 1/2 of the neck with a bushing. When the unsized part of the neck fully expands to the chamber and doesnt spring back, end of soot on the shoulder.

starting to observe a small amount of carbon on some 6BR case shoulders

 

[cw308]

I shoot benchrest 308 only , I'm shooting on the low side of the powder scale because I only shoot 200 yards the max for ranges in my area . I full size from .001 - .002 case headspace no more or less , lm not neck turning or use heat . I use the standard RCBS F/L sizing die with the expander ball , neck tension is .004 I do get some carbon around the necks , no big deal . Never cared for bushing dies , the standard die worked best in every way for me.