The Bureau of Alcohol, Tobacco, Firearms and Explosives issued an open letter on August 28, 2026, telling federal firearms licensees that a complete silencer already registered in the National Firearms Registration and Transfer Record may be repaired or changed to another caliber without being treated as a newly made National Firearms Act firearm. The boundary is explicit: the work cannot destroy the serialized frame or receiver, remove or alter required markings, or otherwise make a new firearm.

That position changes how ATF treats work that previously ran into its April 2008 silencer-repair guidance. The older guidance said replacing the outer tube amounted to making a new silencer. It also treated a caliber change or an increase in the tube's overall length as changes that could trigger NFA marking, tax, and registration requirements. Repairs were generally outside those requirements only when the tube remained in place and damaged internal parts were repaired or replaced one for one.

What manufacturers may now change

ATF's new letter says modifying existing components to change caliber does not create new silencer parts when those components remain in the previously registered complete device. The agency's example is direct: a manufacturer may drill the end cap and baffles of a registered .22-caliber silencer so it can accommodate a 9mm projectile. Because the marked frame or receiver is not affected, ATF says that work does not make a new complete silencer or muffler device.