THis is really not uncommon and while there are times it is caused by small burns in the die, more often then not, it is a result of a much different problem.
You always hear about lubing your case bodies but you should never lube your case necks with a liquid or paste lube or you will get pressure dents in your shoulder. Well, this has some trueth to it but many take this as meaning there is no reason to lube your case necks in any way and this is not true.
As such many just lube the case body and run the case up into the die and over time and many strokes of the dry neck brass over the die, a slight smear of brass will start in the case neck. We are talking VERY small, pin point small.
As time goes on, this little pin ***** sized amount of brass that has attached to the die neck will continue to collect brass as more and more cases are passed over it until it gets to the point that you say, hey, something is scratching my case necks!!!
This can also be caused by not cleaning your case necks before sizing and the abrasive carbon fouling will speed up this occurance and result in the same thing only in most cases over a shorter period of time.
The cure, same as mentioned earlier. Since I have one I chuck the die body up in the lathe, turn it to around 1000 rpms and with some cutting oil and emery cloth polish out the brass. The brass is very soft compared to the die body steel and with emery paper, you would be hard pressed to take any meaningful amount of steel out of the die body, you will polish it up a bit but not much as they are heat treated very hard.
Still, the brass smear will come out easily.
DO not use agressive grit abrasive paper. Anything over around 800 grit, in my opinion is to coarse and not needed.
Again, sounds like the same problem as a burr and the cure is the same, the reason for the problem is totally different.
I recommend lighly lubing your case necks if you are not actually bumping the shoulders back and just neck sizing to prevent this brass build up.
If you are bumping the shoulder, you can use a dry lube such as a quality graphite to lube the inside and outside of the case necks and this will greatly reduce the chance that this will happen down the road.
Kirby Allen(50)
