Barrel Length Restrictions for Suppressors

Nobody knows your suppressor better than the manufacturer who designed it. If this article has done its job, you now have a clearer sense of what you still need to ask, and the right questions to bring to that conversation about whether your suppressor is safe on your specific host. Check with your manufacturer to confirm barrel length restrictions and caliber compatibility of your can.

Case pressure (also called chamber or peak pressure) is the maximum pressure generated inside the cartridge when the powder ignites, peaking very early in the firing event while the bullet is still in the first inch or two of travel. SAAMI specs 5.56 NATO at around 55,000 to 62,000 PSI peak. Muzzle pressure is the residual gas pressure remaining behind the bullet the instant it exits the bore, much lower than peak because the gas has been expanding into an ever-increasing volume as the bullet traveled. The two are linked by gas expansion: peak pressure is set in the chamber and doesn't care what happens downstream, but muzzle pressure falls off as barrel length grows because the same fixed mass of hot gas has more volume to fill. A 5.56 round might exit a 10.5 inch SBR around 9,000 to 11,000 PSI but only 5,000 to 6,000 PSI from a 20 inch barrel, while case pressure stays essentially identical between the two. This is why short barrels are louder and more concussive, and why suppressors have a harder job on SBRs.

You might have noticed that barrels, as they approach the muzzle, might reduce in diameter. This is a simple function of the internal pressures decreasing as more powder is burned off and pressure is turned bullet velocity and heat. Because of this, a suppressor that worked just fine on a long barrel could fail catastrophically on a shorter one. Check out this video by 3RBallistics where he subjects a form 1 Nylon can to an overpressure scenario resulting in a catastrophic failure. Does a can always fail because of an overpressure scenario? Not always. It failure is a function of multiple, potentially compounding forces. Can can that might have be rated for a certain length, if subject to enough heat, could reduce the pressure needed to damage a can.