Here’s a typical cartridge pressure curve. Also, after a certain power level, they weigh more. So why aren’t all guns blowback? Well, blowback guns do have this little tendency to explode if designed incorrectly. The federal government forbids most use of open-bolt (fixed firing pin) designs, since they’re extremely easy to make fully automatic. So you can build working blowback bolts from crappy materials like mild steel (of course, harder steel will wear better).īlowback designs are legal in most US states, as long as you use a semiauto hammer or striker. The force on the bolt face is mostly just compression, instead of the tension at the back of the lugs (see Dan Lilja or Varmint Al for locking bolt analysis). There is no “headspace”, or cartridge slop before the bolt hits the locking lugs. You don’t need to machine locking lugs into the bolt or chamber. There are no mating or rotating parts in fact, the only moving part can be the bolt!
This is a public-domain government publication, so I’m reproducing the figures here directly.īlowback guns are actually a lot easier to build in a garage than locking bolt guns, because: Here’s a schematic view of a blowback gun, from George Chinn’s 1955 masterpiece, “The Machine Gun”, volume 4, part X. “Blowback” guns, by contrast, just use the inertia of the bolt to hold the chamber closed. This includes bolt-action or break-action rifles, as well as rotating-bolt semiautos like the AK or AR. “Most high-powered guns have a locking bolt, where locking lugs hold the chamber closed during firing. Reproduced from the Website “Orion’s Hammer” Massive bolt addition used to harness the 10mm in blowback