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| MAKING A BLOW TUBE FOR BPCR SHOOTING By Wayne McLerran |
Last update: 1/4/2012
As most black powder rifle shooters know, if the bore is not cleaned between
shots, one of the steps necessary to maintain shot-to-shot accuracy is injecting
moisture into the bore to keep the powder and lube fouling soft. Hard fouling
will deform the relatively soft cast bullet, resulting in a loss of accuracy.
When exhaling, the human breath holds a good bit of moisture. Although
simply blowing down the bore from the muzzle may help, 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.
Although a couple of commercial suppliers manufacture blow tubes for
various common calibers, Montana Vintage Arms and Buffalo Arms being the
most well known, making one yourself is relatively simple and may be the
only solution if you’re shooting a less common cartridge. But prior to
discussing the construction steps, some words of caution are necessary
concerning the possibility of getting too much moisture on the chamber walls.
Before constructing a blow tube I suggest you read the article titled: Case
Stretching & Separating in Black Powder Cartridge Rifles. Following is a
photo from Montana Vintage Arms 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.
So now, with the understanding that the goal is to inject moisture into the long
hot bore while minimizing the amount that collects on the chamber walls, let’s
make a blow tube. 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. As noted above, 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, which
was 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 I drilled out the primer hole. 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.
Once the primer pocket hole is enlarged, some shooters have inserted and
soldered in place a brass 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. Following are a couple of photos of a threaded
case and nipple ready for some clear plastic tubing. I “stole” the photos
from Jim Kidwell who posted the idea on the Shiloh Rifle forum.
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. Following is 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 surgical or plastic tubing
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
As most black powder rifle shooters know, if the bore is not cleaned between
shots, one of the steps necessary to maintain shot-to-shot accuracy is injecting
moisture into the bore to keep the powder and lube fouling soft. Hard fouling
will deform the relatively soft cast bullet, resulting in a loss of accuracy.
When exhaling, the human breath holds a good bit of moisture. Although
simply blowing down the bore from the muzzle may help, 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.
Although a couple of commercial suppliers manufacture blow tubes for
various common calibers, Montana Vintage Arms and Buffalo Arms being the
most well known, making one yourself is relatively simple and may be the
only solution if you’re shooting a less common cartridge. But prior to
discussing the construction steps, some words of caution are necessary
concerning the possibility of getting too much moisture on the chamber walls.
Before constructing a blow tube I suggest you read the article titled: Case
Stretching & Separating in Black Powder Cartridge Rifles. Following is a
photo from Montana Vintage Arms 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.
So now, with the understanding that the goal is to inject moisture into the long
hot bore while minimizing the amount that collects on the chamber walls, let’s
make a blow tube. 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. As noted above, 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, which
was 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 I drilled out the primer hole. 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.
Once the primer pocket hole is enlarged, some shooters have inserted and
soldered in place a brass 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. Following are a couple of photos of a threaded
case and nipple ready for some clear plastic tubing. I “stole” the photos
from Jim Kidwell who posted the idea on the Shiloh Rifle forum.
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. Following is 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 surgical or plastic tubing
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
