Legal & ethics — applies to every build in this hub

These rules apply to every build subdirectory under Firearms/. Not legal advice. Re-read before starting any build, especially before machining a receiver-side part or modifying anything that’s already a real firearm.

US-centric (Jeff’s jurisdiction). State-level rules vary substantially and override federal-only assumptions in many cases — when state law is material to a build, the build’s own notes should call it out explicitly.

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Standing rules

1. Know what’s a firearm and what isn’t, federally and at the state level, before machining anything. Under US federal law, a “firearm” includes the frame or receiver of a firearm — not the muzzle, not the grip, not the scope, not the magazine. Machining a Mauser C96 frame in any way that alters its functional characteristics is gunsmithing on a real firearm. Machining a 3D-printed muzzle device to bolt onto that frame is not. The line matters legally, and it matters for which build path (donor mod vs scratch build vs replica) Claude proposes.
2. Replica vs real, treat them differently in the documentation. A “blaster build” in this hub may end up as: (a) a modified real firearm, (b) a deactivated firearm or a legal display-only specimen, (c) a non-firing replica (Denix-style), (d) an airsoft / blank-firing platform, or (e) a wholly fabricated prop with no firing capability. The build’s the build’s own notes declares which it is and the legal posture for that path. Do not assume one path’s rules apply to another.
3. NFA categories Claude must know on sight.
   • Short-Barreled Rifle (SBR) — rifle with a barrel under 16″ or an overall length under 26″. Tax-stamp territory.
   • Short-Barreled Shotgun (SBS) — shotgun with a barrel under 18″ or overall length under 26″. Tax-stamp territory.
   • Machine gun — any firearm that fires more than one round per trigger pull. Heavily restricted; effectively closed to new civilian manufacture under the Hughes Amendment (1986).
   • Suppressor / silencer — any device designed to muffle a firearm’s report. Tax-stamp territory.
   • AOW (Any Other Weapon) — a catch-all category including pen guns, disguised firearms, smooth-bore handguns under 18″, and certain configurations of pistols with vertical foregrips. Some Star Wars prop conversions can drift into AOW territory if not done carefully (a vertical foregrip on a pistol is the classic trap).
   • Destructive device — explosives, grenades, and firearms with bores over 0.50″ that aren’t sporting shotguns.
   • C&R (Curio & Relic) — firearms over 50 years old or designated by the ATF. Most Mauser C96s are C&R-eligible. C&R status changes who can buy / sell / ship the piece but does not exempt it from the rules above.
4. Constructive possession is real. Owning a pistol and a short barrel that fits it and a vertical foregrip can constitute constructive possession of an AOW even if you’ve never assembled the parts. When a build’s parts list could be assembled into something NFA-regulated, the build’s own notes and the relevant volume must call it out explicitly and propose a path that avoids the constructive-possession risk (e.g. machine the muzzle device to be permanently installed on a long-barreled version, sell the donor pistol before machining, etc.).
5. State and local law can override. California, New York, New Jersey, Massachusetts, Hawaii, Washington DC, and others have rules substantially stricter than federal — magazine capacity, “assault weapon” feature lists, replica/realistic-imitation rules, and “any device that looks like a firearm” rules (the latter affecting prop builds, not just live-fire builds). Jeff’s actual state-of-residence rules should be confirmed before proposing a build path that requires shipping or owning a regulated configuration. When unsure, ask before recommending.

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Real firearms vs props vs airsoft — the three legal layers

Path	What it is	Federal posture	State / local concern
Donor-firearm modification (e.g. modify a real C96)	A real firearm. All federal firearm laws apply.	GCA (transfer / FFL rules), NFA (if config crosses a line), Hughes Amendment (no new MGs)	State-of-residence “assault weapon” or feature laws, magazine limits, may need transfer through an FFL even within-state
Deactivated / display-only specimen	A firearm-shaped object that ATF / state has accepted as no-longer-functional	Federal: depends on the deactivation standard. Many “deactivated” specimens still count as firearms federally; UK/EU deactivation standards do not.	State law varies widely on what counts as deactivated vs. still-a-firearm
Non-firing replica (Denix, etc.)	Cast / machined metal or polymer shape that physically cannot chamber or fire a cartridge	Federal: not a firearm. Subject to Toy Gun Marking Act and Federal Toy Gun Safety Act rules in some configurations (orange tip rules apply to imitation firearms under 15 USC 5001).	NY / NJ / CA / MA have rules on “imitation firearms” that can affect possession and transport
Airsoft / blank-firing conversion	A platform that fires either 6mm BBs (airsoft) or blanks (no projectile, plug-throat barrel)	Federal: airsoft is not a firearm. Blank-firing guns are usually not federally regulated unless readily convertible to live fire. Some Russian-made blank-firers have been imported and ruled “readily convertible” by ATF — those are firearms federally.	Often regulated as imitation firearms; orange-tip rules may apply
Scratch fabrication / prop-only (no firing of any kind)	A machined / printed / laser-cut object that bears no functional firearm component	Federal: not a firearm. Toy Gun Marking Act and the Federal Toy Gun Safety Act / 15 USC 5001 may apply if it’s a realistic-imitation firearm.	Same as non-firing replica — state imitation-firearm rules apply

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Sources to consult (and not invent)

When citing the legal posture in a deep dive, cite primary sources, not memory-of-memory:

• 27 CFR Part 478 — GCA implementation. Defines firearm, frame/receiver, modification rules.
• 27 CFR Part 479 — NFA implementation. Defines SBR / SBS / suppressor / MG / AOW / DD categories and tax-stamp procedures.
• 18 USC § 922 — federal prohibited-person rules, interstate transfer rules.
• 18 USC § 921 — definitions (this is where “firearm”, “antique firearm”, “destructive device” are statutorily defined).
• 15 USC § 5001 — imitation firearms / Toy Gun Marking Act.
• ATF Open Letters and Determination Letters — these are how ATF tells the industry “yes this is an AOW” or “no this is fine” on specific configurations. Searchable on atf.gov. Cite the letter number and date.
• ATF Form 4473 / Form 1 / Form 4 — purchase, make-an-NFA-item, transfer-an-NFA-item respectively. Reference by number when describing process.

When the deep dive references a state rule, cite the state statute by number, not a third-party summary.

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