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GUNS Magazine March 2010 - Page 35
• Jeff John • Q: I recently read John Barsness’s article “Ahh, Sweet 16” on handloading Chamber length Johnloads16-gaugeammotofittheratherwidevarietyofchamberlengthsfoundinhisguns whichinclude(fromtop)aBritisharmy&navySxS,Germancombinationgunwitha9.3x72Rrifle barrel,ithacaModel37andtheWinchesterModel12.Photo:JohnBarsness the “middle” gauge in the August 2009 issue and recently acquired a 16-gauge Hunter Arms “Fulton” SxS with 2-9/16" chambers. I have gotten conflicting reports on whether it is safe to shoot modern 2-3/4" shells. Most sources seem to say this is not much of an issue in 2-9/16" chambers, but can be in shorter 2-1/2" chambers developing dangerous pressures. Isn’t the difference between 2-9/16" and 2-3/4" shells only 3/16"? I have seen 12-gauge shells with seemingly more variation than that. However, I’ve seen vintage 1960s boxes of 2-3/4" 16-gauge loads state “Danger—do not use in chambers shorter than 2-3/4"!” Mr. Barsness says, “While some pressure tests show no real danger in shooting 2-3/4" loads in such chambers…” he does suggest reloading to shorter length for guns so chambered. I am interested in buying factory loads for my gun and other publications specializing in double guns and wing shooting seem to support Mr. Barsness’s statement about it not being dangerous. I’m not sure if it is worth the trouble and expense of getting the chambers lengthened if I don’t have to for safety reasons. The gun is in otherwise good working order and I don’t plan to put anything but regular lead field loads through it. Adam D’Amico via e-mail A: Let’s ask John Barsness: The problem with short chambers and modern ammo is it’s filled with variables. While all the pressure-tests I’ve found (including those made by major ammo companies) indicate there’s either no pressure rise— or maybe 1,000 psi—when firing 2-3/4" shells in 2-1/2" or 2-9/16" chambers, that doesn’t mean there never could be. WWW.GUNSMAGAZINE.COM I’ve done considerable measuring in trying to figure out why such a pressure rise would occur. In modern shotshells one issue is the “hard” rear end of a plastic wad. This isn’t easily compressed, and when forced through a “short chamber” forcing cone already partly filled with the front end of a plastic case, obviously can result in higher pressure. Also, the rear diameter of different wads varies considerably, mostly due to whether they’re designed to be used in molded cases with tapered interiors, or Reifenhauser cases with straight-walled interiors. The smaller diameter of a tapered-case wad might not cause any pressure rise at all, while the larger diameter wad from a straightwalled case might. These various factors are probably the source of the 1,000 psi pressure rises seen in some gun/ammo combinations. A mitigating factor is many “short” chambers are actually longer than stated. I’ve measured the chambers of a bunch of old American shotguns, as well as many British and European guns, and I don’t recall ever measuring one actually 2-1/2" long. Most so-called 2-1/2" chambers in British guns have measured 2-9/16" to 2-5/8", and often the two chambers in a double are slightly different lengths. The supposed 65mm (2.55") chambers on one of my old German drillings actually measure around 2.7", which is darn close to 2-3/4". Obviously such longer chambers are less of a potential problem. And yes, there are considerable differences in the actual length of fired shotshells. When loading for my German drilling I simply select Federal cases measuring 2.7" or less. I’ve also measured a lot of shotgun bores, and most European 12-gauge bores are smaller than the nominal American .730", while most European 20-gauge bores are bigger than the nominal .615" used in American guns. Obviously a smaller bore with a short chamber will probably cause higher pressures. Sixteengauge guns from anywhere are all over the place. The last factor is the quality, age and condition of the shotgun itself. This can also be all over the place, whether we’re talking about an old American double used with black powder ammo and not cleaned often enough, or a quality British double that’s had the bores repolished so often the barrel walls are almost paperthin. Yet another factor is European and British ammo is normally loaded to lower pressures than American ammo. All of which is why many of us suggest either shooting shotshells that match the chamber, or having the chambers lengthened. While shooting longer shells won’t cause any problems 99.9 percent of the time, the slight chance of a real problem isn’t worth the minimal cost of buying or loading shorter shells, or having the chambers lengthened. Aside from possible damage to a useful shotgun, our forend hand is right where most barrels blow out. If you don’t want to load your own shotshells, I would suggest having the chambers in your Fulton lengthened. This isn’t expensive, and a normal (and pleasant) side-effect is lighter recoil.— John Barsness Questions and Answers Due to the volume of mail received, GUNS cannot offer a personal reply. Please e-mail your question to ed@ gunsmagazine.com or snail mail to: GUNS Q&A, 12345 World Trade Drive, San Diego, CA 92128 35