From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Subject: Re: lathe marks in cylinders
Organization: Lawrence Berkeley Laboratory

In article <38762@mimsy.umd.edu> paull@hplred.hpl.hp.com (Robert Paull) writes:

#  Does anyone know why there are circular cuts directly behind the chamber
#mouths in a revlover cylinder? It seems like all revolvers have what look
#like rough lath cuts right about where a case mouth would stop. I thought
#these cuts might be to help keep the case from moving back in the cylinder 
#when the cartridge is fired. Since the case expands (obdurates?) to fill the

Obdurate is what _I_ am; you mean obturate.  8-{)}

#cylinder the case mouth would lock into the cuts and be held. The only
#problem with this theory is, as we know, the case really does slam
#back against the breech face as the bullet leaves the case.

A very small point - the machine which chambers a cylinder isn't a lathe,
it's more like a mill.  Certainly you'd use a lathe to chamber a rifle,
but it would be a royal pain to do a cylinder this way.

First the chamber is rough-bored and then it is finish reamed or in the 
case of S&W, sometimes ballized.  In some instances the manufacturer is 
not finishing the chamber to full depth.  This isn't too surprising 
because the far end of the chamber is the hardest part to do well.  Most
manufacturers use a finishing reamer which includes the forward part
of the chamber and all of the rest of the part of the bore which is in the 
cylinder.  This doesn't always fix the problem because these reamers are
very slightly tapered to ease case extraction so this means that the part
of the chamber nearest the rear of the cylinder has been gently eased out
as the wider part of the reamer reached it, while the forward area hasn't
had this benefit so it stays rough.  I've found that if you go slowly 
enough with a fresh, sharp chambering reamer, you won't have this problem.
To fix this problem, I've used a copper lap and very fine grinding compound.
For a low-tech fix, wrap some 600 grit paper around a dowel and go after it.
Just make sure you don't make the forward part of the chamber larger than
the rear.  This makes extraction too interesting.

     JHBercovitz@lbl.gov    (John Bercovitz)

From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Subject: Re: Getting crud out of cylinders
Organization: Lawrence Berkeley Laboratory

In article <38761@mimsy.umd.edu> paull@hplred.hpl.hp.com (Robert Paull) writes:

#  I've noticed that after I shoot 50 to 100 rounds of .38s' in a .357 
#(158gr LSWC) a ring of what appears to be carbon, lead or some 
#other fouling builds up behind the chamber mouths. This is tough stuff.
# [stuff deleted]
#   Recently I took a resized-deprimed .357 case, flared the mouth slightly
#and soldered an 8 inch piece of brass tube to the rim. I dip the case in
#solvent or Breakfree and push it into a cylinder. The slightly flared case 
#scrapes the fouling off the walls. The loose fouling is removed by running a
#patch thru the cylinder. This is the best method I can come up with so far.
#I assume that the brass case won't scratch the cylinder walls.
#   I would like to hear about your cleaning techniques and if there's an
#easier or better way to clean cylinders.

That sounds like a great way to do it.  I gotta try that.  What I do is use
a cleaning rod section with a brass brush on one end and a hand drill on the
other.  Works good.

        JHBercovitz@lbl.gov    (John Bercovitz)