Heavy Carbon on necks


Well-Known Member
May 2, 2009
Central Oregon
I was working up some loads for my AR30 338LM and noticed that only cases with carbon fouling on the necks was with Retumbo.
As it is, there are no pressure signs and these are the most accurate loads so far.
I am loading 97g to 98g of retumbo.

Is this anything to worry about?

When my 338 LM started doing this it was because the brass was getting hard and needed annealed. The case was not sealing to the chamber as good as it use too. This started at about 4 firings.

Have a look at my response here (I'm 284win):
.338 LM smoked necks - Sniper's Hide Forums

It's a common problem with the 338LM and Retumbo. Retumbo is a very slow burning powder. If you read my reponse to that thread, more powder solved the problem, but I think you might be getting near the hot side. Which bullet are you using?

I can almost guarantee you have a factory chamber. With too much neck/chamber clearance, heavy 338LM brass, and a slow burning powder, your are not getting a good neck to chamber seal. If you're happy with the accuracy I woudn't sweat it.

The fireforming process might have something to do with it also. Your brass needs to be fireformed to your chamber. I often get smoked necks when fireforming.

Hope this helps.
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More neck tension, hotter primer, seat bullet deeper, faster burning powder or you can steelwool your necks between reloads.
Thanks for the reply's.

I am using the 250g smk's.
When I take a headspace measurement on new brass (2.313") and once fired (2.316-319"). I am loading them out to 3.140" at the Ogive, this is .020 off the lands.
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I shoot Retumbo in my 243 and have the same issue also with my 284 Win. here's a little trick that I found out several years ago, soak the brass in Apple Cider Vinagar, about 30 - 45 minutes stirring about every 15 then was off in clean water several time and chunk em' in the tumbler they come out all nice and pretty! just do this outside as you don't want to get those looks from the other person that lives with you :D I can't say enough to wash several times in clean water. Later,

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