III. Firearm Information by Type

D. Rifles

1. Commonly Available Cartridges

a. An Examination of Norinco 7.62*39 Corrosiveness

It seems that every couple of weeks we get a message here wanting
to know if the Norinco 7.62x39 FMJ ammo is corrosive.  I mentioned
here a few months ago that I was going to perform some simple
tests in an effort to ascertain this.
 
I performed a test on the Norinco 7.62x39 FMJ ammo that I bought 
recently and it certainly produced no corrosion.
 
NOTE: The ammo I refer to is copper-washed steel (case and bullet)
with steel-cored bullets which is sold in caselots (wooden) of 1200
rounds.  Inside the case the ammo is boxed up into yellow cardboard
containers with a styrofoam insert (20 rnds/box).  Each round is
stamped with the characters:   311 (or maybe 3II) and 92.  The
cardboard boxes clearly state that this ammo is non-corrosive (but
I didn't believe that until I'd tested it for myself).
 
This test consisted of shooting a couple of hundred rounds through
my SKS then scraping the residue from inside the gas tube and piston
onto one of three plates of plain steel.  One of the other plates
had common salt sprinkled on it and the other was left untouched.
 
Prior to the test all three plates were scrubbed and degreased then
dried in an oven at 200 deg Celsius for 30 minutes.
 
After the salt and powder residue was applied, all three plates were
again baked for 20 minutes at 200 deg Celsius and then removed and
left out in my garage for three days (it's summer here and the temp
has varied from about 15 deg C at night to 25 deg C during the day
and we have had rain on two of the days).
 
After the three day period I observed the following results:
 
PLATE 1 (the control, untouched steel)
Small spots (pinhead size) of rust were observed on the surface of
this plate.
 
PLATE 2 (sprinkled with common salt)
Spots of rust were noticeable.  These spots were somewhat larger
than those of the control plate and were more obvious where the
crystals of common salt were concentrated.
 
PLATE 3 (powder residue)
In areas exposed to the air (ie: not covered in residue) the rust
patterns were identical to the control plate (ie: small pinheads)
Where the metal was covered by the powder residue however, the
steel was *LESS* affected by rust although there was an even layer
of "tarnish".  This tarnishing was certainly not as deep as the
pitting produced by the rust spots found on the exposed areas on
all plates.  It would appear that (in this case) the residue was
almost providing a barrier between the air and the steel and a
level of protection from rust.
 
CAVEATS:
This was hardly a carefully monitored "lab-level" experiment and
despite the fact that we had a couple of small showers of rain
during the test period, the humidity overall was quite low during
the three days the plates were left exposed.
 
Testing was forced to a conclusion on day 3 when my wife "tidied up"
the exposed plates, contaminating the salt and residue covered ones
by stacking them face-to-face on my bench :-(
 
Since this experiment seemed to confirm that the ammo is non-corrosive
I've taken to cleaning my SKS with conventional techniques and
materials.  Now I just use Hoppes #9 on the barrel and gas-system.
The first time I did this I checked every day for a week to make sure
that no corrosion was occuring.  None was found and a re-clean on the
fifth day resulted in clean patches first time through with not a hint
of rust.
 
DISCLAIMER:
Since Norinco seem to be packaging their 7.62x39 ammo in a number of
ways (stripper clips, galvanised boxes, green card & wax paper, yellow
cardboard & styrofoam, etc) I'm not about to put my head on the block
and say to everyone that it's safe to assume *all* this ammo is non
corrosive.  All I'm saying is that the batch I've got seems to offer
no threat to the life of my rifle when I use normal cleaning techniques.
 
This may be somewhat academic since it seems that the supply of 7.62x39
FMJ into the US has all but dried up (for once I'm glad I don't live
in the USA.... we have no such problems here).