Strange mark on necks

[SBfan]

I have been getting a black mark on the necks of my 222 brass after annealing. The mark covers about a third to half of the circumference of the neck. The odd thing is that I only get the mark on Lapua brass and not on RP or WW. All brands of brass are annealed the same which adds to the mystery of the cause of the marks. Anyone have an answer as to the cause? In the photo the 4 cases on the left are RP and the 5 cases on the right are Lapua. The 5th. Lapua case shows how the mark does not go completely around the neck.

 

[Bill Norris]

I have been getting a black mark on the necks of my 222 brass after annealing. The mark covers about a third to half of the circumference of the neck. The odd thing is that I only get the mark on Lapua brass and not on RP or WW. All brands of brass are annealed the same which adds to the mystery of the cause of the marks. Anyone have an answer as to the cause? In the photo the 4 cases on the left are RP and the 5 cases on the right are Lapua. The 5th. Lapua case shows how the mark does not go completely around the neck.

Looks as if it could be a carbon trace being brought out by annealing and showing up on the Lapua brass. Different manuf. will have different amounts of components in the brass.

 

[Dave M.]

I was also thinking Carbon marks. Especially considering the remark about the marks not going all the way around the neck.

 

[Dusty Stevens]

Strange

 

[SBfan]

I don't think the marks are carbon as I clean, with ss pins, before annealing.

 

[RegionRat]

What method are we discussing? Flame, induction, other?

It isn’t uncommon with flame for reloaders to get a different pattern to the coloration on the surface. We are typically looking at variations of the subscripts in the oxides that occur at different temps and thickness.

The vast majority of the time, it is purely cosmetic and no effect on the annealing. As long as the piece is rotating in the flame for a balanced exposure, or fairly well centered in the field of the induction coil, it usually isn’t a problem.

To tell the difference, see what happens if you scrub very gently. It shouldn’t take much scrub to take the oxide layer down below the level where the color survives. OTOH if it is tenacious and deep, it may be a problem and in some examples means the anneal may be uneven.

Odds are against the bad outcome, but let’s hear what you say before we give further advice.

 

[SBfan]

I'm using flame to anneal and the cases rotate during exposure to the flame. I just tried RegionRat's suggestion and spun a case, by hand, a couple of times in a medium steel wool. This was followed by a couple of turns in 4 O steel wool. The result was that 98% of the mark was gone. I'm curious as to why the mark does not go all the way around the neck.

 

[ronemus]

The flame creates a hot spot which moves as the case is rotated, so there is a temperature gradient when the case drops; this causes the variation in color that you see. My guess is that carbon is deposited on the cold neck by the flame and only burns off on part of it. Try annealing a bit longer to remove the black part. Lapua brass usually has a thicker neck than other brands, so unless you turn them all to the same thickness the Lapua brass will be cooler in a fixed annealing cycle. You can either neck turn or adjust the annealing time to reach the same endpoint.