Black deposit in the bore and on case necks - bullet lube?

[Alex Hamilton]

Hi, Guys,

I was at Bisley yesterday to test a new load combination for my 308Win target rifle and after 15 rounds I noticed dark "smears" in the bore about 2" from the throat. 2"beyound that the bore was clear. I also had a very similar black depodit on case necks. When I got home I pushed through a piece of paper kitchen towel wrapped round the jag and the deposit in the bore was removed completely. It also rubbed of easily off the case necks. The deposit was only on the parallel sides of the neck. Nothing on the shoulder, nor on the rest of the case. My gut feeling is that it was bullet lube, but I would appreciate your views.

The load was Lee 310160R bullet, cast in pure linotype, gas checked and lubricated with NRA 50-50. The powder charge was 27grs of Accurate 2015 (aka Lovex S060) in Prvi Partizan cases and large rifle primers. I had no usual indicators of high pressure. In fact, I would have said that the load could take another grain of powder, because I saw a few unburned powder granules in the bore. Accuracy was excellent at 200yds - about 2MOA group, despite fishtailing wind from 6 to 9 o'clock.

The barrel groove size is .308" and the barrel is very little used. One pass of the paper wrapped round the jag restored the bore to mirror finish and I could not detect any slivers of lead on paper patch.

If any expert on this list could clear up this mystery, I'd be very grateful.

Best regards,

Alex in UK.

[nvbirdman]

Sure sounds to me like carbon deposits/unburned powder. Maybe burned up boolit lube. Since the accuracy is good and it wipes right out, I wouldn't worry about it.

[hickfu]

How many time has the brass been reloaded? full length sized or neck sized? I only ask because it sounds like work hardened brass that is not sealing the chamber fully... I got this from new Starline brass in 45-70 (they even say you should anneal it on their site)

You may want to try annealing it to see if it is blow back because of not sealing properly...
Just my .02

Doc

[454PB]

I'd say "not to worry" if it's shooting that well and not leading. What diameter are you sizing?

[Alex Hamilton]

I'd say "not to worry" if it's shooting that well and not leading. What diameter are you sizing?

The bullets are sized to .310" and the groove size is .308. I was getting slight leading with bullets sized .309", which disappeared as I went up a .001".

[Alex Hamilton]

How many time has the brass been reloaded? full length sized or neck sized? I only ask because it sounds like work hardened brass that is not sealing the chamber fully... I got this from new Starline brass in 45-70 (they even say you should anneal it on their site)

You may want to try annealing it to see if it is blow back because of not sealing properly...
Just my .02

Doc

You are very probably right. My annealing ability is pretty primitive - kerosene blow torch with the brass standing in 1" of water, but it is worth a try to clear the mystery. I will also try increasing the powder charge in hope that the higher pressure will obturate.

[sigep1764]

So I posed the same question last week. The advice i was given was to load and shoot and swab the bore with a patch. Patch sure smelled like my bullet lube and all of it wiped out super easy. I was concerned it was leading, but it certainly was not. Smell the patch and let us know. I gotta tell ya, this site made the leap into casting so doable with the willingness of these guys to share info/teach. Just reading on the different subjects covered will steer most around any trouble.

[quilbilly]

Sure sounds to me like carbon deposits/unburned powder. Maybe burned up boolit lube. Since the accuracy is good and it wipes right out, I wouldn't worry about it.

I agree. Sounds similar to my 308 with the same Lee boolit but a little less in the bore but the accuracy is excellent. I am using a softer alloy however.

[captaint]

sigep - Sounds like you got it right, my friend. I mean the part about reading your a$$ off before you get asking the mundane questions. The questions are fine, but I prefer to see some do some serious reading first. That's what I did back when. I certainly asked SOME mundane questions, I did keep it to a minimum. If one simply does the reading exercises first, almost every question will be answered then.
And you're right, these guys are terrific here. They know their stuff and they pass that knowledge out freely. Continue to enjoy. Mike

[sigep1764]

Thank you sir. Appreciated.

[tomme boy]

What kind of brass?

[runfiverun]

PPU tommy.

[tomme boy]

PPU is usually a soft brass. And generally thick like Federal. So, I guess it is just a lube issue. As long as you don't get a hard build up from the lube, keep shooting. I would make sure to clean the bore after shooting though.

[madsenshooter]

I get that all the time, takes quite a bit of pressure to fully expand the neck, more than what most cast bullets will stand. It only became a problem to me when I was full length sizing my cases and shooting some low pressure loads. I noticed the front half of my cases were looking weird. I found that lube had been flowing back into the chamber, and I'd not cleaned it for awhile. I had a reamer that easily pulled all the lube out without doing any chamber cutting. Now I neck size and the deposit doesn't go beyond the shoulder of the case.