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.