What causes this?????

[JDL]

This PM I was shooting my .358 Win. with the Lyman 358318 HP boolit booted out with 23 grains of 2400. I noticed something shiny on the neck and shoulder of the fired brass, and on closer inspection, found it was streaks of lead. It was very thin, almost plating, but would peel off easliy with thumbnail pressure.
I've never noticed this on any other rifle I shoot and was wondering if anyone had an explanition. Thanks- JDL

[stocker]

Same reason as low pressure loads commonly collect lots of powder residue on the necks. Basically not enough pressure to develop a tight case neck to chamber seal and lead scraped off the bullet by the lands is being forced by gas back between the case neck and the chamber. Not a problem and a green scouring pad cleans both lead and powder residue from the case quickly.

[Iron River Red]

It happens to me when I don't take my time seating my bullets. I get shaved lead and it shows up later.

Might be worth looking into.

[Buckshot]

.............Similar to Stockers suggestion could be that if your chamber mouth has a ledge at the beginning of the throat, exposed by caseneck expansion. I don't know the pressure involved with 24 grs of 2400 but it would be considerably more then 24grs of 4198, which would be a good load. It could very well be the base is upsetting and shearing some lead off on that ledge, and being carried back by gas flow?

Since I think that charge sould definetly be sufficient to cause the caseneck and shoulder to seal, possibly the lead you see on the case is from the previous shot? Just guessing here.

.............Buckshot

[stocker]

Buckshot:

When this has occured in my rifles I find the lead spread around the neck shoulder junction very thinly. If those tiny lead shavings stayed solid they might not reach there even with what appears to be reasonable charge of powder.

As the lead is only about .004 thick and quantity is quite small and right in front of the flame I have believed they are converted to liquid form and that would let the lead flow back to where I find it from pressure in the barrel. The case neck may even be retracting a bit at that point due to the relatively brief duration of pressure.

Certainly some ball powders can soot up a case neck even with max charges behind J-bullets which also tends to make me think case neck retraction occurs pretty quickly. Might be tough making M-guns cycle at the rate they do if that wasn't the case.

Thoughts??

[StarMetal]

Yeah, I have some thoughts, if it is indeed lead slivers, such as Buckshot theorized and some were measured as thing as .004, I can see how the pressure from the gases could force those slivers between the neck and the wall of the chamber, possibly even plasticizing those slivers to make it appear as a plating.

Joe

[slughammer]

Thoughts??

Do a pound slug or a chamber cast to see how sharp the junction is or isn't. See what diameter the throat is. IF the junction is sharp and the boolit is big, it will shave off what it wants. In fact, sharpness and a lack of concentricity may be enough to do it irrelivant of boolit size.

[AnthonyB]

I'll chime in and give you my thoughts. I think the problem is the 358318 HP mold. We all know HP molds are very slow to cast with, don't drop bullets of very consistent weight, and are a PITA to keep up to temperature to ensure good fill-out around the pin. Now we can add lead slivers on the case neck to all the other problems associated with HP molds. I have several HP molds I bought to keep them out of circulation and prevent other casters from experiencing these problems, and you should probably sell the troublesome thing to me. Tony

[Bass Ackward]

I've never noticed this on any other rifle I shoot and was wondering if anyone had an explanition. Thanks- JDL

JDL,

You are getting poor ignition. Surprised? It can happen even with fast powders. Either use a larger diameter bullet or seat out and touch the lands. Problem will disappear.

Oh by the way. What you see on your necks is also in your chamber.

[Cherokee]

I have only encountered this in hot 32-20 revolver loads in my Ruger SA. The cylinder throat ledge must have been shaving lead and the high pressure forced it back onto the case mouth. Never had any back on the neck itself, just the first .004 of the case mouth. At lower power levels with the same bullets, didn't happen. BTW, the loads were very accurate.