Gunsmithing  LMT MWS .308 Excessive carbon in barrel/LC-LR pulled brass neck sealant?


Full Member
Jul 24, 2014
Houston, TX
This weekend I went and shot my MWS that I haven't fired in over 6 months, testing a new smaller aperture gas tube, and trying to get my Gemtech/JP HP bolt/Firing pin to actually cycle more than a few shots. I used ammo I loaded last year with LC-LR (new/pulled brass) and Hornady 168 HPBT bullets that I regularly take to 1000 yards in my bolt gun. It's loaded warm, to about 2750 fps (I think the charge is 48.6 of PP2000MR.

I wasn't sure the last time I cleaned the barrel, but thought maybe 400-600 rounds prior, and since I ran a few of these suppressed, the upper was filthy. (I had FTE/FTF with the Gemtech carrier in the suppressed setting, and case head damage using the JP HP bolt, so I switched back to my LMT carrier. (no issues)

I go to clean, and I'm running patch after patch of C4 through the barrel (over 50 of them) and patches are still coming out completely black. (no stripes...full black) Over and over I'm running patches, then bronze brush over 50 strokes with C4. I've gone over 60 patches by this point and decide to switch over to CLR (SS barrel so it should be fine)

I run patch after patch of CLR and still getting full black patches coming out. Over 50 patches of CLR (I cleaned my brake spotless prior to attacking the barrel to ensure I'm not getting false carbon fouling) I decide to plug the bore, and fill it with CLR to leave overnight.

Next day I unplug the barrel, and this black sludge is coming out. Completely black, it looks like runny tar. I then remember that the LC-LR brass I processed for this load is pulled brass, which has the tar/lacquer sealant in the necks, of which I mostly removed using q-tips and acetone, and most of it burned off when I annealed them. So I'm thinking, maybe this fouling is part carbon/part sealant. Is this possible? By the way, my third day in, I'm still getting carbon on my patches, albeit much less. (Just streaking rather than full black patches) I flushed the barrel with Hoppe's foaming bore cleaner and then a crap load of Hoppe's 9 to make sure the CLR is gone.

Last night I switched to JB bore compound/Kroil and VFG pellets thinking it needs more scrubbing, and it seems to have helped some. I cleaned out the JB with Kroil patches and switched back to C4 for a few more passes.

I've now started attacking some of the copper with Eliminator, but still getting carbon along with some blue copper signs. Is this normal fouling even for a barrel which might have 500 or more rounds through it without cleaning (it shoots sub-moa last range trip) Is it possible that the neck sealant remnants on the LC-LR brass might have something to do with it? (I've shot this ammo through my Proof bolt gun and haven't had this issue) I know I'm overthinking it, and it doesn't need to be clean to shoot it, but wanted to take it down to bare metal and at least clean the carbon out. I'm not concerned about copper at this point.

Is PP2000 MR that dirty? Should I even care? Barrel shoots lights out most of the time but is picky about loads. I didn't borescope it prior to cleaning cause I don't want my borescope mirror to get crap all over it. I'll borescope it after I'm done, if that ever happens.

I've added photos of what it looks like now and discovered this weird buildup in the chamber (neck area) The photos are AFTER about 150 patches or so. I should warn ppl, be careful with CLR in semi-autos because even though my barrel is SS, the extension is phosphated steel or something, and the CLR must have creeped all over it, down the extension, into the barrel mating area and retention screws, seizing the entire barrel assembly tight. I couldn't even remove one of the screws but was able to coax it out with a brass punch. Eventually the barrel broke free and I immediately cleaned off any rust that had already formed, doused everything in alcohol followed by Kroil. That weird buildup must be fumes or rust from the extension that must have migrated down or something. I can't explain it. I cleaned the area out and scrubbed it with Boretech eliminator and the "buildup" came out but the area is stained black. Super weird. Anyhow, the rest of the barrel has this "fuzzy" texture as if it's been powdercoated in carbon or something. Patches are coming out gray-ish, but still not clean. I've never seen anything like this. There is no exposed metal in the bore at all. I've also never shot moly coated bullets if that's what it would look like, but I did shoot a box of Winchester silvertip last year out of it (black coated bullets, not sure if moly)

Has anyone see something like this? Shoots fine, but if I'm devoting time to cleaning (4 days now off and on) I want a bright bore so I can start over. I know ppl will say to not worry about it, just shoot it. I don't want to leave this shit in my barrel when I put it in the safe for another year.


  • LMT MWS Bore Carbon Baked.jpg
    LMT MWS Bore Carbon Baked.jpg
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  • LMT MWS Chamber Area.jpg
    LMT MWS Chamber Area.jpg
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  • LMT MWS Gas Port Carbon Baked.jpg
    LMT MWS Gas Port Carbon Baked.jpg
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