Sometimes it’s not the gun, it’s the ammo

By Hamilton S. Bowen, GUNS Magazine

Gunsmiths are much like farmers. They have to know a little about everything. Every good gunsmith and every good farmer is a Jack of all trades. In addition to a thorough understanding of firearm mechanics, gunsmiths need also to know a great deal about ammunition. Practicing gunsmiths encounter nearly as many failures of munitions as guns in their day-to-day practice. In many cases, a gun is “repaired” simply with a change in diet or some related adjustment to the ammunition. We’ll touch on a few common problems and how to overcome them.

Before SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) was founded in 1926, headspace allowances, essentially cartridge endfloat in the chamber, tended to vary from maker to maker and gun to gun. It isn’t uncommon to see a vintage Winchester or Savage lever rifle with what today would be considered excess headspace, whether from manufacturing tolerances or just wear and tear. With low-pressure ammo of the day, this really didn’t hurt anything until and unless the owner started reloading his own ammo. Then, the sloppy chambers would tend to stretch the cases on firing. Full-length resizing the cases after a few firings would often lead to case-head separations just forward of the rim, leaving the balance of the case stuck in the chamber.

Happily, there is an easy fix for reloaders. Have your gunsmith check the headspace to verify it is long and out of spec. While ideally you would have him set back the barrel and repair the excess headspace, this is often a time-consuming and costly process—and unnecessary. The simplest fix is fit cases to the gun. Using fresh unfired or once-fired cases, expand the necks up three to four calibers, then run them into your full-length sizing die only enough to form a new shoulder forward of the original. Leave it long initially, checking fit in the rifle. The action must not close at this point. Slowly, a little at a time, size further until the action just closes. Use this die setting to size fired cases in the future.

A really scary example of problems arising out of vintage guns and ammo are the province of big-bore British magazine rifles. I have seen serious function problems in custom rifles that were positively in spec according to best available chamber and headspace numbers and had adequate firing pin protrusion. Not all factory ammo made for the .404 Jeffrey, .416 Rigby, .505 Gibbs and other similar rounds is all that well-matched to available rifles. With some currently-produced ammo, I have seen numerous failures to fire or hang-fires due to short body sections exacerbated by the extremely sloped shoulders of the cases, all adding up to excess headspace induced by the ammo. You haven’t lived until you have experienced a 0.08-second hang-fire in a .505 Gibbs. Using our neck sizing technique will create ammo with proper headspace for these guns. I would never venture into harm’s way with a big-bore dangerous-game rifle for which I did not personally load the ammo, carefully tailored to the specific gun.

As a practicing revolver schmidt, I see several common “gunsmithing” problems almost daily that are the result of reloaded or out-of-spec ammunition. Heavy-bullet high-performance ammo is all the rage today in sport revolvers. Most of this ammo is loaded with cast bullets, which quite often have quite wide front driving bands in front of the case mouth. If this section of the bullet is too long and not sized properly, it can foul on the leede or throat sections of the chamber, preventing the cartridge from fully seating in the chamber. Sometimes, the interference is great enough to prevent closing the cylinder. Even if you can close the loaded cylinder, the cases may still have interference headspace and the gun won’t cycle smoothly.

Assuming the throat diameters are adequate to the bullet diameter below the crimp, the solution is either to properly size the whole cylindrical section of the bullet or change to a design with a smaller meplat and narrower driving band. Reloaders often forget that in-and-out bullet sizer/lubricators do not always size the entire bullet due to lube port location or bullet length. Only through-type sizers will accomplish this. A simple remedy is to use the Lee bullet sizer die in a reloading press to complete the job.

In some cases, reloading practices are not at fault. Gun malfunctions are just plain bad luck, a combination of unhappy gun and cartridge specifications. The resident baby Nambu is a good case in point. Available custom ammunition tends to have a long cartridge body section, which prevents the gun from going into battery occasionally. The ammunition may well have perfect specifications but my particular gun has seems to have short headspace and simply won’t function with it. Running the fired cases through the standard full-length sizer die didn’t help. So, I simply shortened the die body until I could set back the case shoulder enough to produce ammo that works. This same problem cropped up recently in the shop with a .38-40 revolver and was solved with exactly the same die modification. Vintage rounds were developed before the advent of SAAMI and chamber and ammo specifications varied wildly, leading to incompatibility of some ammo and chambers.

Every gunsmith and gun junkie should have as much ammunition-related material as possible in his archives. The book Cartridges of the World is a must-have and good place to start. If you shoot vintage firearms, old loading manuals are invaluable sources of loading data and bullet mold info. I also have several volumes on vintage ammo that I visit regularly. Aside from a set of high-quality calipers and a precision micrometer graduated in “tenths,” one of the most important tools you can have is a set of SAAMI cartridge and chamber drawings. Happily, these are now available on the Internet. These drawings are God for contemporary cartridge specifications and are binding on firearms manufacturing industry members. They also make life a lot easier for us small fry out here in the trenches.

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For more information:

Cartridges of the World
F+W Publications, 700 E. State St.
Iola, WI 54990
(715) 445-2214
www.gunsmagazine.com/gun-digest-4

Lee Precision 
4275 Highway U, Hartford, WI 53027
(262) 273-3075
www.gunsmagazine.com/lee-precision

SAAMI 
11 Mile Hill Rd., Newtown, CT 06470
(203) 426-4358
www.gunsmagazine.org/saami