Firearms come apart when gas pressures from burning powder can’t leave soon enough. Time matters. Pressures can’t build to dangerous levels if you don’t give them time.
On the other hand, you must give pressures time to build to useful levels. The bullet is an obstruction. Its resistance (friction and mass), plus barrel length and the relationship of bore to case capacity determine the appropriate powder and charge. A charge of fast-burning Bullseye powder behind a lightweight bullet in a .45 ACP pistol generates a sharp, quick thrust. It must, because that short bullet is easily dislodged.
As it races through the short bore, a huge space opens instantly behind it. The powder has little time to work before its energy dissipates. Think of a ping-pong paddle in action.
A rifle powder such as 4350 in a bottleneck case like a .270 generates pressure more slowly as it burns. The bore is small, relative to case capacity, and the bullet long. An instant burst of energy from Bullseye wouldn’t give the sustained push needed to overcome bore friction and accelerate the long, slim .270 bullet through a long barrel.
Heavier charges of fast powder would lift pressures to dangerous levels. Bore space behind the bullet wouldn’t increase fast enough to relieve it. Think of that ping pong paddle meeting a baseball. The paddle (or your wrist) would yield before the momentum of the incoming ball could be reversed.
Like handgun ammunition, shotshells use faster powders than those in bottleneck rifle hulls. The heavier the shot load, the slower the powder. Short pressure curves don’t mate well with slow acceleration against high resistance. Also, shotgun barrels and/or actions weren’t designed to bottle stiff pressures. Big bores and straight cases flush pressure out fast.
Rifles of modern steel seldom come apart. Acceptable breech pressures of smokeless centerfire rounds as determined by SAAMI (Sporting Arms and Ammunition Manufacturers Institute) run from around 42,000 psi for the .30-30 to over 60,000 psi for high-velocity magnums.
Several bolt rifles safely digest proof or “blue pill” loads of more than 100,000 psi. Famously, Springfield 1903 receivers to serial number 800,000 (in 1917) were of case-hardened, low-carbon steel, not as strong as subsequent double-heat-treated receivers. These acceded to even stronger nickel-steel receivers at serial number 1,275,767 (in 1927).
Proper charges of proper powders help keep your rifle intact. But careless mixing of cartridges can make even safe loads hazardous. Once a pal inadvertently loaded a .308 round in his .270. The .308 cartridge is shorter, so the bolt closed before the bullet met the smaller neck of the .270 chamber.
When he fired, pressures vaulted as the .308 bullet squirted through the .277 bore. The bolt froze shut. Gas from the ruptured case blew the extractor off and jetted through the magazine well, splitting the stock into three pieces. Fortunately, the Mauser lugs did not fail, and my friend was wearing glasses.
Another way to blow a rifle is to not use any powder at all. Once, having heard only the hammer fall as I triggered a borrowed rifle, I opened the action and ejected a fired case. “Must have forgotten to cycle the lever,” thought I, and chambered another round. But just before I fired, another possibility came to mind. Action open, I looked into the bore. Dark.
The rifle’s owner had failed to add powder to that first case. The primer had driven the bullet inches into the bore. Had I launched another 200-grain softpoint, pressure would have spiked as it collided with the stuck bullet. The Model 71 Winchester would almost certainly have been ruined, with injuries likely.
Don’t use someone else’s handloads! Pull the bullets; use the components.
You’ve read caveats about firing smokeless loads in Damascus shotgun barrels – those made by wrapping heated bars around a bore mandrel. The rule makes sense, as does the use of black-powder or “smokeless for black” (not full-power smokeless) loads in old double rifles. In truth, some early rifles and Damascus shotguns thrive on modern ammo.
I have it on good report that the actions and barrel thickness of Parker shotguns dating to the early 20th century are such that Parker proofed to higher pressures than generated by modern target loads, even some duck loads!
Still, barrel steels of a century ago don’t match ours today. Breeching that has become loose, or weak cases or oversize or damaged chambers add risk. When in doubt, have the gun examined by people with appropriate equipment and expertise, or stick to mild loads.
Hewing to conservative loads in old guns, and taking care to use the right powders and ammo can keep stock and steel in one functional piece, and you, too.
Learn More About Reloading
For reliable reloading information, look to the Reloader’s Special bundle from GunDigestStore.com. It includes The ABC’s of Reloading book, Reloading Shotgun Ammunition DVD and Reloading for Handgunners book.
About the Author: Wayne van Zwoll is a regular contributor to the Gun Digest annual, and author of the Gun Digest Book of Sporting optics. He is a nationally-recognized expert on rifles, optics and western hunting.
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