Soot on neck?

[dgibson]

Everybody's opinion now: what's the significance of "soot" on the neck of a fired casing? The ones in question are .270, nickel-plated brass, factory loads, average but not stellar accuracy out of an average but not stellar gun.

 

[dgibson]

Come on, folks; help me win this bet. You're costing me money! NOBODY has a reason why a spent casing would have burnt powder soot around the neck or whether it's important?

 

[MLM]

Morn dgibson, I only have two rifles that do not leave some soot on the neck. They are tight neck chambers. All of my hunting and factory rifles leave from a very small amount to being down right dirty. When firing the round the shell casing must expand like a gas bag to seal the chamber. The neck being the hardest part of the brass is realy the hardest and last to expand. You can control this to a point with powder choice and seating OAL, but not get rid of it completly. I hope this helps and don't cost you any money. It is just my 2cents worth.
Mike Murphy

 

[dgibson]

Thanks, Murph; even just the part about most of your rifles doing the same thing saved my $. A guy I know was really carrying on about his rifle doing that (not really even that bad), how the throat was too long and the headspacing was messed up and how it was just a matter of time blah blah blah....So, the bet.

 

[Delw]

Does it do it with brass case's or just the nickle ones? Nickle is alot harder to expand than brass is..


Delw

 

[dgibson]

Hey Delw--it does it on both brass and nickel. The nickel is more pronounced, but I think that's just as much from the color of the case as anything. That's what set him off to begin with; he had been shooting brass for a while and hadn't really noticed the soot, but he tried some Win Supremes in their nickel-plated cases and it really stood out. (Pretty case not shiny any more!)

 

[danr55]

Gibson, The fact that there is soot on the neck and none on the shoulder disproves your friends theory about head space being messed up. If the head space was messed up, there would be soot on the shoulder and down the sides of the case, or he would not get the bolt closed. Usually, that indicates that the case neck contract back to normal size after firing before the bullet has exited the barrel. There is still fired powder smoke cooking in the barrel and the exhaust from that burning is deposited on the case neck. If you think about the order of events that take place after you pull the trigger, that would be about number three or four. It's a good thing. If the case doesn't contract back a little bit, it usually indicates that the brass is hardened and may be on the verge of cracking or that the neck of the chamber is so tight that you may be increasing pressure more than is needed because the case neck can't expand enough to release the bullet completely.