STRETCHING SHORT BRASS TO FIT YOUR BPCR CHAMBER By Wayne McLerran
Last update: 6/7/13
In an earlier article posted on this site titled Shooting Short-Case Cartridges in BPCR’s – Myths & Facts, I discussed the subject of firing “short-case” ammo. The bottom line is it will not damage the chamber but expect accuracy to suffer to some degree. In another article titled Case Lengths, Chamber Casts & Impact Impressions, I covered several techniques to determine the exact length of your chamber and the preferred overall “fire-formed” case length. So, assuming you've measured the chamber and determined that the bunch of expensive brass you have is too short, what are your options?
You could purchase new brass, which may not solve the problem. The chamber may be longer than available new brass or longer than specified by the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI). And even if your chamber is SAAMI compliant, it’s very common to find new factory brass shorter than the SAAMI specifications. Of course, assuming it’s available; you could buy new brass for the same caliber but for a longer chambering and trim it shorter. An example is buying .45-90 brass to use in a .45-70 chamber after trimming. But this article is not about buying new brass. I will cover the three techniques that I’m aware of to lengthen the cases you already have.
Prior to discussing “realistic” options for stretching cases I’d like to dispel any thoughts you may have of attempting to significantly stretch brass using unorthodox loading or chambering techniques. Brass can be “fire-stretched” by using a combination of heavy neck tension, crimping the bullet and lubricating the chamber wall, but it will take several firings to stretch it a significant amount. Plus the likelihood increases that the case will completely separate. I suggest you read the article I wrote some time ago titled Case Stretching & Separating In Black Powder Cartridge Rifles.
Case Stretching Options
Note - Should you succeed in stretching brass using one of the techniques discussed below, keep in mind that the ideal case overall length (COL) should match the overall chamber length after “fire-forming” and/or neck expanding, certainly prior to full length resizing which will lengthen the case a few thousands.
I’ve used the .45 caliber stretcher and it does work, but it’s more work intensive and not as fast as the Kal-Max jig discussed below but much less expensive. Also, if you plan on stretching brass that has been fired and resized a few times, properly annealing the neck area prior to stretching will likely be necessary to reverse the work hardening and sufficiently soften the brass. Following the instructions, many strokes of my Redding T-7 turret press were required to stretch new .45-70 Remington brass 0.010”. One has to definitely develop a “feel” for when the stretching is taking place. The brass is stretched in the neck region. The process not only uniforms the neck wall but also thins the neck wall slightly, which may or may not be an advantage depending on your chamber and bullet dimensions. The Remington brass neck wall thickness went from 0.0105” to 0.0095” as the case was stretched 0.015”. Continuing the process, I was able to stretch annealed cases 0.030” with a resulting neck wall thickness of 0.0090”. Additional stretching may be possible, but I quit after reaching 0.030”. Tim suggested that the max he would recommend stretching Remington brass is 0.025". He also indicated that a liberal amount of case lube, more than would be used just resizing the brass, makes the stretching noticeably easier. Tim uses RCBS water soluble Case Lube-2. I used what I had handy, which is RCBS's original case lube (not water soluble).
Kal-Max Case Stretching Jig (KMCSJ) If your short brass is Remington, Starline, Winchester or Bell brand in .38, .40 or .45 caliber, another option is to purchase the Kal-Max Case Stretching Jig. I highly recommend the KMCSJ for stretching brass, but considering the price ($185 + shipping at the time of this writing) plus the additional hydraulic pump and ram unit ($100 to $250), it may not make sense to purchase the setup to stretch a hundred cases or so. Once the jig and ram are set up and adjusted, the stretching process is relatively fast. For a short video showing the KMCSJ in actual operation go to http://www.youtube.com/watch?v=oGzQsrPT4Qs or http://wn.com/Kal-Maxavi. The hydraulic pump and ram (the two orange-colored units in the video) are not included with the KMCSJ and must be purchased separately or rented.
For pricing and more details on the KMCSJ, go to http://kal.castpics. net/CaseStretcher.html or contact Charlie (Chuck) Maxwell (aka Montana Charlie) at firstname.lastname@example.org. There’s more than one source of a suitable 4-ton hydraulic pump and ram. Porto Power makes one (also sold by Sears), but the best deal I found is the Central Hydraulics Portable Puller (model # 44899) from Harbor Freight. I picked up one on sale for significantly less than the regular price of $99.99. You may also be able to rent one from a local equipment rental company.
Using the KMCSJ I stretched brand new .45-70 Remington brass 0.008” at the minimum setting and 0.037” at the maximum setting. The brass was not annealed. The potential stretching range depends on the wall thickness at the central portion of the case. Within the total range the amount stretched is determined by the adjustable punch. The punch comes with several thin washer- like spacers. Maximum stretching is achieved when the punch, with no spacer, is seated as deep as possible in the case. Due to the tapered walls of the case (walls get thicker towards the rim) the deeper the punch seats in the case the more it stretches the case as the punch and case are forced through the die. The finished brass no longer has tapered walls where it was stretched. The case wall thickness in the neck region is not changed.
Kal-Max versus Tim Smith-Lyon’s Stretcher As noted in the above comments, the price, complexity, and the stretching process are different between the two solutions. Also, the location the brass is stretched is different. As displayed by the dark case discolorations in the following photo, the Kal-Max stretches the brass in the middle; the Smith-Lyon’s unit stretches the neck area. By the way, the discolorations were the natural result of brass oxidation over several months after being stretched. The discolorations will be easily removed during normal cleaning in a vibrator or tumbler.
Stretching Brass with a Lathe If you’re fortunate to have a lathe or a friend that has one, brass can be lengthened using a “nib & spin” technique. The process involves the use of a die to hold the case and a “nibbing rod”. The nibbing rod is similar to a boring rod but has a very smooth hardened bump on one side close to the end, or has a hardened ball bearing seated on one side to form the bump. A die, similar to a full-length resizing die, is constructed to rigidly house the case and keep it from turning inside the die. The die inside diameter (ID) must closely match the outside diameter (OD) of the case. The die and case are aligned and clamped in the chuck jaws. Once everything is setup, the nibbing rod is inserted deeply into the case at a point where the case wall is thicker. As the lathe is running the nibbing rod is adjusted so that the bump or ball bearing presses against the wall of the case and slowly “irons out” or thins the wall as the case spins and the rod advances towards the case mouth, hence the term “nib & spin”. As the wall is thinned the excess brass is forced forward lengthening the case. I have not tried this technique, but likely will once I get my lathe up and running.