I have noticed that the necks on my brass are turning black after they are shot. Is it some kind of blow-back? My tumbler won't get it off with corn-cob media with polish. Is there something wrong with my reloading process, or is it normal?

Quite normal for the necks to get black. That's what gets the blowback at discharge and before the neck is expanded and seals off the rest of the gases. Easiest way to get rid of it is to carry a 35MM film can with a rag saturated in Kroil, or a bore cleaner. Do it at the range before putting away the brass to bring home.

Another way is to use a piece of a Scotch Brite pad with a bit of solvent on it.

Blackened necks is also a sign of a light loading, provided you aren't seeing signs of pressure or at max charge try going up a grain or so and see if they go away.

Take some 000 or 0000 steel wool and just twist the neck a few times and it will take off the burnt powder. With neck sizing dies, that is the only cleaning I do with the cases and with my reloading they still turn black with hot loads. Good Luck

Thanks, so it's normal. Some rounds are dirtier than others that is what got me wondering. As for light loads, these are on the upper end. Not max loads, but not light either.

what mark said..

generally, unless you have an autoloader, blacked necks are a sign of too low pressure. This is misleading, especially when combined with a slightly sloppy chamber.

I've found that just about any bore cleaner, wiping them down at the end of the range session, works fine.

jeffe

I use the maroon colored scotchbrite. I don't even bother with solvent. A quick twist over the neck and ready for the sizing die.

In general, you'll see more of it, the more clearance there is between the neck and the chamber. HTH, Dutch.

Even with max loads, slow burning powders may have a slow enough pressure rise that gas leaks back along the neck before the pressure rises enough to obturate the neck against the chamber wall.

Lighter loads=lower pressures not only seal the case less to the chamber wall but it (sometimes) has an inperfect combustion (lower pressure=lower heat) producing huge amounts of smeary-sticky soot which need more than a bit of steel wool to get it off.

When you use steel wool, do not forget to clean the cases afterwards with a piece of cloth or your dies will not stay in perfect shape for long.

1894,
please edit your post to show your words and mine.
jeffe

Several years ago I did experiments with a .300 Weatherby to determine whether I could make loads that produced 30/06 velocities from it, with good accuracy. One of the powders I tried in these experiments was Varget. I found that using it in reduced loads with 180 grain bullets in the .300 Weatherby -- loaded down to produce velocities in the 2600 to 2700 f.p.s. range -- produced loads that gave good accuracy, but the dirtiest cases I've ever seen.

My conclusion is that some powders tend to burn dirtier than others, and reduced loads tend to produce dirtier cases than full-power ones, probably because the case isn't sealed against the chamber wall as well as it would be in a full-power load.

I don't think there is any harm, other than an aesthetic one, from dirty cases and dirty case necks. I agree with those above who say that you can use a chemical cleaner or steel wool to get rid of it.

[ 10-28-2003, 20:56: Message edited by: LE270 ]

I will give the steel wool and cleaner a try. My guess is that it may be sloppy chambers because the loads are not light. I get black necks on my 22-250 and my 7mm stw. I don't have my loading data here at work, but I think the 22-250 is shooting ~~ 36 grains of H4895 under 50 grain v-max (load right off the container) and the 7mm stw is shooting a max load in my rifle of 81 grains IMR7828 under 140 grain partitions.

I have found some rounds and some guns are more prone to this than others. Some rounds, specifically that those are more prone to case stretching, and therefore require more frequent trimming will experience a thinning of the brass in the neck area sooner than otherwise. Holding fixed the neck-cut of the chamber, it stands to reason that the case neck must expand further before it seals. Hence, the other variable is how tight the neck-cut of the chamber is. I am conjecturing here...

I am not certain that pressure has all that much to do with it, per se. I have long been fond of shooting low pressure loads in the 8x57 (35,000 CUP or so), and have found that the cases necks blacken no faster than any other round.

Brass flows towards the neck, thickening rather than thinning it. This is for all bottle-neck cartridges, not just those with tapered bodies that tend to stretch the most.

Interesting.

I just measured some 250 savage cases (which should flow quite severly), and the necks were indeed thicker after a few firings.

However, I just measured some 284 cases, and the opposite was true. Perhaps the 35-degree shoulder allows less of the case brass to flow forward of the shoulder?

On another note, perhaps the more fired brass is less pliable, and is therefore makes a lesser quality seal in the neck area when fired.

If you don't want to have to scrub your cases, or do the other remedies, consider going to a faster powder. Eg< If you are using 4350 try using 4895 instead. I have done that. I try using mid range to fast powders in all my reloading instead of the slow popular powders 4350, 4831 etc.

I also do not think corn media cleans worth a darn in comparison to walnut. After I started using Walnut, I gave away the remaining corn media I had that was still new. The used stuff I just tossed.