Zero-Dollar Stamp Could Finally Make Captive Piston Ammo Legal to Sell

This week's Silencer Saturday column on The Firearm Blog digs into captive piston ammunition, a century-old idea for suppressing a gunshot inside the cartridge itself, and asks whether the NFA's $0 tax stamp finally clears the way for it in the US.

Key points

• Old tech, new relevance: Daniel Y notes the design dates back to a 1902 J.E. Bissell patent, predating the Maxim silencer, and was famously used in the Soviet PSS pistol's SP-4 round, which traps propellant gas with an internal piston instead of a muzzle-mounted can.
• Why it never caught on here: The article explains that the ATF has treated each individual captive piston cartridge as its own suppressor, requiring a serial number and, until this year, a $200 tax stamp per round.
• What changed: With that stamp eliminated on January 1, the piece argues these cartridges could now move over the counter on a Form 4473, though they'd still be serialized firearms subject to background checks.
• Still a hassle, just a different one: The column points out a 4473 can list unlimited items, so a box of rounds could transfer on one form, but FFLs would have to track every serial number in and out.
• Reusable rounds: Daniel Y floats the idea that reloaders or manufacturers could repack spent cartridges, letting hunters carry a few suppressed rounds alongside standard ammo for the same rifle.

Quick take

It's a neat regulatory loophole more than a product announcement right now. Nobody's selling captive piston ammo at your local counter yet, but the legal logic the article lays out is sound, and it's worth watching if any manufacturer decides to test it.

Read the full story: Daniel Y