Lead on my case mouth: Pic attached

[12DMAX]

Ok I think I posted this before but I for the life of me can not find it so one more time. What is causing this? All is kosher when seating as in I do not see any lead being shaved off bullets all seem to seat nice and smooth, no build up at all in my die. The pictures are fired cases, this is when it shows up.

[wallenba]

It's only a guess, but I'd think it is transfer from the neck area of the chamber. Somehow previous firings may have deposited it there. Shoot some jacketed and see if it still happens.

[I'll Make Mine]

Another possibility is this: if you're using a combination seating/crimping die, the case mouth starts to crimp before the bullet stops pushing in. If the die is adjusted a tiny bit short, this will result in the case mouth starting to cut into the crimp groove (adjusted a little shorter still, or with a case that's a little longer, it'll cause shoulder collapse), and the expansion of the case on firing may plate a little lead onto the mouth as you see. Solution: either trim your cases, if they've gotten a little long, or adjust your seat/crimp die for a little less/later crimp, or change to seating and crimping in separate operations (two dies, by preference, or adjust the die to not crimp while seating, then remove the seating plug and adjust to crimp on the next pass).

[12DMAX]

Another possibility is this: if you're using a combination seating/crimping die, the case mouth starts to crimp before the bullet stops pushing in. If the die is adjusted a tiny bit short, this will result in the case mouth starting to cut into the crimp groove (adjusted a little shorter still, or with a case that's a little longer, it'll cause shoulder collapse), and the expansion of the case on firing may plate a little lead onto the mouth as you see. Solution: either trim your cases, if they've gotten a little long, or adjust your seat/crimp die for a little less/later crimp, or change to seating and crimping in separate operations (two dies, by preference, or adjust the die to not crimp while seating, then remove the seating plug and adjust to crimp on the next pass).

I thought of this also but i seat and crimp seperatly. I did just notice it on my 357's also so maybe what wallenba suggested could be the culprit.

[I'll Make Mine]

Even if you seat and crimp in separate operations, you could get rings like this from crimping too hard (in both rifle and .357). If you have good neck tension (especially in a rifle) you really only need to take off the mouth flare. Recoil in a revolver and magazine conditions in the rifle might militate needing more crimp, but in a rifle, a roll crimp is usually the wrong kind (roll crimp is what's been recommended in revolver rounds for decades, but adequate neck tension will reduce the crimp requirement -- that bullet just has to avoid pulling out for five shots unless you top up your revolver).

Overcrimping, especially in the rifle, could come from case stretching (which comes from full length resizing that sets the shoulder back), if you've had cases that have been fired a number of times since you adjusted your dies. Alternately, deposits in the chambers could come from cases that are shorter than the current bunch, just due to over trimming or cases from different sources or lots.