Image credit: Lynndon Schooler Good afternoon, everyone, and welcome back to TFB’s Silencer Saturday, brought to you by Yankee Hill Machine, manufacturer of the new Victra 20-gauge shotgun suppressor. This week we are looking at an uncommon but clever method of suppressing firearms. Captive piston ammunition suppresses the shot by containing the sound inside the cartridge. For regulatory reasons, this has never caught on in the United States, but with the recent changes to the NFA, there's no reason now why it couldn't. Let's discuss.Silencer Saturday @ TFB:Silencer Saturday #454: 375 Raptor Silencer Saturday #453: NFA Sea Change In Wake Of ATF Guidance LetterSilencer Saturday #452: Silent But Deadly Subsonic Rifle Match Silencer Saturday #451: Return of the LVAW Silencer Saturday #450: 4473 vs. Form 4 TransfersDisclaimer: This is not legal advice, and you should not rely on it to take or not take any action.Captive piston ammunition is relatively uncommon, but it is hardly new. There is a patent from 1902 by J.E. Bissell depicting the technology in a lever-action firearm. This actually predates the Maxim silencer’s patent in 1909. Several firearms have incorporated it in their design, with possibly the most famous being a clandestine handgun used by the Russians. Our writer Lynndon Schooler profiled the Soviet PSS pistol and its captive piston ammo earlier this year. His description of that ammunition deserves a quote here:“The most interesting aspect of the PSS is its departure from most suppressed weapons of the era in that it does not rely on a large, external suppressor to deaden sound. Instead, the pistol uses the SP-4 captive-piston cartridge that traps propellant gases inside the case with an internal piston at the moment of firing. That internal piston drives the bullet out of the case and then comes to rest, sealing the gas inside and preventing the high-pressure gases from exiting the muzzle, the principal source of a firearm’s report and flash. By confining the expanding gases within the cartridge, the SP-4 reduces signature while keeping the weapon compact.” PSS with SP-4 captive piston ammo (Lynndon Schooler) Another very good analysis of the PSS and its ammunition can be found in this article in the Small Arms Defense Journal. It also includes a cutaway view of the SP-4 cartridge. It is well worth a look if you want to see the inner workings.Unfortunately, this technology has never been widely available here in the United States. With our regulatory structure, each individual cartridge was considered a silencer by the ATF. That meant a $200 tax stamp and a serial number on each individual cartridge.On January 1 this year, that $200 tax stamp went down to zero. We had posited that perhaps this would mean captive piston ammunition hits the market on some level. Now that the ATF is no longer requiring Form 4s to transfer these items, they could be sold over the counter on a Form 4473.This would still not be the same as buying a box of your favorite ammo and heading off to the range. Each cartridge would still be serialized and would still transfer as a firearm. Under federal law, the ATF enforcement decision does not extend so far as to remove these items from the Gun Control Act, so the standard firearm purchase, transfer, and background check would still apply. However, Form 4473 has multiple lines for a reason: you can transfer an unlimited number of firearms on one 4473. There is even a specific form that you can add to your 4473 to add additional lines, so buying a box of 20 rounds of captive piston ammunition could easily happen in one form. It will just make your local FFL bothered because they will have to keep track of each of those serial numbers, logged in and logged out.But there's another thing about captive piston ammunition: it is not inherently a one-time-use item. There is no reason why, with the appropriate tooling and supplies, a skilled reloader could not reload their own cartridges or, failing that, could not send it back to the manufacturer for repacking. With that approach, the logistical headache of obtaining the serialized cartridges is more of a one-time hassle than a per-shot hassle.Consider the possibilities with this. Currently, if I have a gun like a 300 Blackout with a silencer, I can switch back and forth between subsonic and supersonic ammunition. Those have different points of impact and very different ballistic curves, but they still can be fired in one firearm.With captive piston ammunition, I can take my standard hunting rifle, which has no silencer attached, and continue shooting my regular old .30-06 ammunition. I could also have a few rounds of captive piston .30-06 in my hunting bag, and if I want to switch to suppressed use, I just have to dump the magazine and throw in the captive piston rounds. This will again change the point of impact and the trajectory, but that is no different than switching between supers and subs in a rifle with a silencer attached.Thanks for joining us for another edition of Silencer Saturday. What do you think? Will captive piston ammo become more common? Or will it remain a footnote despite the new regulatory environment? SILENCER SHOP – HANSOHN BROTHERS – DEADEYE GUNSMAC TACTICALALL YHM PRODUCTS AT BROWNELLSDEALERS: If you want your link to buy YHM suppressors included in future Silencer Saturday posts, email: silencers@thefirearmblog.com