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MAKING A BLOW TUBE FOR BPCR SHOOTING
By Wayne McLerran
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,
Wayne
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.