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By Wayne McLerran
Last update: 7/28/13

It doesn’t take long for a black powder rifle shooters to realize that if hard
fouling builds up in the throat or bore, accuracy quickly suffers.  Therefore, if
not wiping between shots, somehow moisture must be injected into the bore to
keep the fouling soft.  When exhaling, the human breath holds a good bit of
moisture.  Simply blowing down the bore from the muzzle may help, a

common practice of 19th century hunters, but it’s not sufficient for most
conditions and is not a technique that’s compatible with prone BPCR silhouette
competition.  It’s much easier and quicker to insert a “blow tube” into the open
breech end of the barrel after the spent case has been extracted.

A couple of commercial suppliers manufacture blow tubes for various

common calibers, Montana Vintage Arms and Buffalo Arms being the most
well known. But making one is relatively simple and may be the only solution
if you’re shooting a less common cartridge.  Below is a Montana Vintage Arms
photo displaying a selection of their blow tubes.  Since the anodized aluminum
inserts are machined to minimum dimensions to slide into most chambers for a
specific cartridge, the O-rings stop air flow and moisture from blowing back
past the end of the tube into the chamber.  Locating the rings close to the tip is
not critical since the air flow is completely stopped.

Blow Tube Construction:
 To construct the most common style of blow tube you’ll need a standard
cartridge case, clear plastic tubing and a nipple of some type to slip the tubing
over.  To maximize air flow go with the largest diameter nipple that will fit.  
The case should extend the full length of the chamber, certainly not shorter than
the case length of the cartridges being shot in the rifle.  To match the chamber
dimensions as close as possible the case should be “fire-formed” in the rifle
being shot and not resized.  Even better, since the brass will shrink slightly in
diameter after fire-forming, use a neck expander to slightly flare or “bell” the
mouth until the case just barely but easily slips fully into the chamber.

An alternative to fire forming is to resize a new case using trial and error to
determine the correct resizing die setting in order to minimally reform the case
so it just barely slides fully into the chamber.  If the diameter of the case neck
or mouth ends up too small afterwards, use an expander die to enlarge the neck
or mouth to the maximum diameter that will fit.  Slightly flaring or belling the
mouth may also result in a better fit.

The next step of drilling out the primer hole is likely the most challenging of
all.  It can get a little “tricky” trying to hold or clamp the case without
deforming it while enlarging the primer hole.  I used a wooden dowel inserted
into the case for the 1st blow tube I made.  The dowel was quickly formed by
hand on a vertical belt sander.  For subsequent blow tubes I held the case in
one of those hammer-type impact bullet pullers; wrapping a thin folded piece of
fine sand paper around the case just in front of the base helped to hold the case
from rotating as the primer hole was enlarged.  No doubt there are other
innovative methods to hold the case.  When drilling out the primer hole, start
with a small diameter drill and work up in small increments to the largest
diameter required.

Once the primer pocket hole is enlarged, some shooters insert and soldered in
place a common brass yard hose splicer as the tubing nipple.  A more elegant
solution is to drill and tap the hole to fit the tapered threads of a 1/8” copper or
brass pipe nipple that has been cut in half (see photo below).  One advantage of
using a screw-in short pipe nipple is you can take it apart and resize the case if
it gets damaged.  If it does get damaged, since fire forming is no longer an
option, use the alternative trial and error case forming method mentioned
earlier.  I may use this construction method for future blow tubes due to the
advantage of being able to easily repair a bent tube.  It also allows for easy
cleaning by unscrewing both parts and tossing them into the cleaning media
when cleaning cases.  The photo below displays a threaded case and nipple
ready for some clear plastic tubing.

Another option is to cut off the end of the pipe nipple and solder or braze the
nipple to the case rim.  Or use a standard plumbers flaring tool to flare and
flatten the end of a short piece of copper tubing and soldered it to the case rim.  
And yet another method is to drill out the primer hole of two cases and solder
the rims together back-to-back.  Then shorten the case that was not fire-formed
and slip the tubing over it.  This latter method provides for a larger hole,
allowing for maximum air flow.  Once the case and nipple section is finished,
slip the plastic tubing over the nipple and you’re ready to go.  If necessary,
heat the end of the tubing in a small pan of water to soften it.  Below is a photo
of the 1st .40-65 blow tube I made.  The ¼” (0.375” OD) copper tubing nipple
was pushed into the enlarged primer hole and soft-soldered in place.

A Couple of Final Suggestion:
Regardless of the blow tube construction, keep the nipple and tubing as short as
comfortably possible in order for most of the moisture to reach the bore rather
than condense on the inside of the blow tube.  If you decide to make your own
blow tube, make two in case one is damaged during a match.

In closing, I should mention that some shooters apply the “KISS” (Keep It
Simple, Stupid!) principal and never go to the trouble of making a blow tube
with a cartridge case.  They just cut off a piece of clear tubing of the
appropriate diameter and shove one end into the rifle chamber.  If the tubing is
the correct diameter and the end is cut square, it should create a seal when the
end contacts the transition step from the chamber to the throat or bore.  In fact,
this simple approach should work as well or even better than making a blow
tube with a brass case or aluminum insert.

Wishing you great shooting,