From: andrew, [EMAIL PROTECTED]
The cause of the leading in the cylinder throat is
probably down to the bullet being too hard and not
fitting the throat. I used to see this all the time
with low pressure loads and bought bullets which were
invariably cast from very hard alloys. Basically the
bullet is not sealing the throat and gas is escaping
around the bullet eroding metal from the bullet side
which is then deposited on the barrel surface
immediately ahead of the bullet. For a long time I had
this problem with my M29 and 250 gr. swc's and 18 gr.
of N110 which gave a pleasant 1300 fps. The bullets
were correctly sized for the chamber throats but I got
heavy lead deposits in the forcing cone. When I read
of the relationship between chamber pressure and bullet
hardness I tried cutting the wheel weight alloy with a
large lump of pure lead and the leading problem
disappeared. I also tried upping the chamber pressure
to shoot the bucketful of bullets I already had on
hand and this worked too.
The problem is that if the bullet is too soft then
whilst the bullet seals off the gasses at the breach
the seal is degraded as the bullet goes up the barrel
due to the bullet not being able to support the shear
stress imparted by the rifling. Essentially a small
amount of slippage takes place which opens a gap on
the trailing edge of the groove pressed into the bullet
by the rifling, gas can again get by eroding bullet
material and depositing it on the barrel surface ahead
of the bullet.
So the rule is, assuming a correctly fitting and
lubricated bullet, leading at the breech - bullet too
hard or not enough pressure. Leading at the muzzle -
bullet too soft or too much pressure. When you get
this right you can basically forget about barrel
cleaning. After I sorted out my M29 I only cleaned it
about every 5000 rounds, and that was only because I
was feeling guilty!
Please bear in mind that the lead is removed from the
bullet by an erosion process, it is not melted though
it might become molten once liberated from the main
body of the bullet.
> Many interesting comments have been made regarding
Vihtavuori powders but no real explanation has yet
been forthcoming of why I experienced ferocious leading
with N310 powder but not with Hercules Bullseye - all
other components in the equation being the same. Whatever
the mechanism that is causing the leading, it must be
associated with the powder as nothing else has been
changed.
What is the betting that the N310 produced a slightly
lower pressure at the critical time when the base of
the bullet needed to be upset to seal the throat. This
is yet another example of difference in behaviour
between seemingly similar powders.
< There was no velocity leading in the barrel.>
I don't know what Velocity leading is.
After some 40 shots the leading was a highly visible
thick layer, effectively soldered' to the chamber throats
and was very hard to remove. >
Try a lump of steel wool wrapped around an old bore
brush. Works a treat!
Cybershooters website: http://www.cybershooters.org
List admin: [EMAIL PROTECTED]
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