Liquid nitrogen gun barrel dip?
Donald R. Newcomb
man did to get a rifle barrel to shoot accurately. One thing he mentioned
was sending it off to be dipped in liquid nitrogen. Now, I asked a
mechanical engineer I know what this does and was treated to a long
discussion of the cryogenic properties of metals which left me more
bewildered than before.
Can someone give me a simple explanation of why chilling a barrel
in liquid nitrogen would make it shoot better? Thanks.
--
Donald R. Newcomb * University of Southern Mississippi
dnew...@whale.st.usm.edu * "The God who gave us life gave us liberty
dnew...@falcon.st.usm.edu * at the same time." T. Jefferson (1774)
W. Sugai
Donald R. Newcomb <dnew...@whale.st.usm.edu> wrote:
#A an article in a recent Precision Shooting Magazine discussed things on
#man did to get a rifle barrel to shoot accurately. One thing he mentioned
#was sending it off to be dipped in liquid nitrogen. Now, I asked a
#mechanical engineer I know what this does and was treated to a long
#discussion of the cryogenic properties of metals which left me more
#bewildered than before.
#
#Can someone give me a simple explanation of why chilling a barrel
#in liquid nitrogen would make it shoot better? Thanks.
i'm afraid i can't help you with the nitrogen-dip question but i do
recall from my shooting days that the single biggest factor affecting
accuracy in precision bench rifle shooting had to do with the way that
the internal stresses in the barrel caused stringing as the barrel heated
up with repeated shots fired. the smith that spoke to me about this
embellished his account with the tale of how the "old-time" barrelmakers
(pope, et al.) would throw the barrel blank on the floor a few times to
relieve the internal stresses. perhaps this nitrogen-dip technique has
something to do with relieving internal stresses, but if it doesn't, i'm
sure my remarks will invite rejoinders anyway, thereby keeping this group
active. :-)
Russ Kepler
W. Sugai <wsu...@eskimo.com> wrote:
#In article <3bqlrg$3i...@whale.st.usm.edu>,
#Donald R. Newcomb <dnew...@whale.st.usm.edu> wrote:
##Can someone give me a simple explanation of why chilling a barrel
##in liquid nitrogen would make it shoot better? Thanks.
Cryogenic cooling can help in stabilizing metals, and is used in very
high precision work (usually at the gage level, about .000001 in 1"
level). I'm not aware that a barrel is critical in this dimension, and
know that consistency in the barrel exceeding .0001" through the
entire bore is considered pretty good (the best barrels are lapped
to better than that).
So, I'd work on a lot of other things on a rifle before I went to the
bother of doing a cryogenic treat on the barrel (heck, most problems
are bedding, trigger or shooter anyway, even with the real precision
shooters). I'm not sure that there is a shooter in the US that would
be able to see the difference (against the noise induced by wind,
powder variation, bullet variation, temperature, barrel temp, feeding
irregularities, primer differences, primer seating differences, case
differences, bolt set changes, action shifts, etc.)
--
Russ Kepler posting from home ru...@bbxrbk.basis.com
Please don't feed the Engineers
George C. Rybicki
bbxrbk!ru...@basis.com writes:
##In article <3bqlrg$3i...@whale.st.usm.edu>,
##Donald R. Newcomb <dnew...@whale.st.usm.edu> wrote:
###Can someone give me a simple explanation of why chilling a barrel
###in liquid nitrogen would make it shoot better? Thanks.
I don't know if it will make it shoot better but this is what it
does to the metal.
Gun barrels and transmission gears etc are sometimes made from air or oil
hardening
steels. The steel is worked in a softened or normalized condition, it is
then heated back up and transforms to a high temperature form of iron
called austenite. On cooling back down
the steel transforms into ferrite and martensite. Martensite is a very
hard phase of iron.
The steel (martensite) is then tempered to reduce brittleness.
Occasionally all of the austenite does not transform to ferrite and
martensite at room temperature, this is bad
news, so we cool it down in liquid nitrogen so all of the austenite is
transformed. The condition is called retained austenite and is bad for
fatigue and fracture properties of gears. I dont know how it affects gun
barrels, but there is a volume change on the transformation of austenite
to ferrite and martensite so maybe it has a small affect on the
dimensional stability of the barrel. I am skeptical though because it is
usally something like 2% retained austenite or less than that.