FirearmsModule 6.4~7 min read

AR-15, Rails & Magazines

Serialized parts are irreversible

AR-15 lower receivers and serialized parts cannot be replaced if you ruin them. Altering or engraving over a manufacturer's serial number is a federal crime in the US. Always test settings on the inside / hidden surface first. Customer-supplied serialized parts: get signed liability release, photograph before work. ATF compliance for any serial number application is your responsibility. Verify minimum depth + character height requirements with current ATF guidance and consult an FFL attorney for compliance questions. See Disclaimer & Liability for full terms.

Aluminum receivers and Picatinny rails are easy work: soft material, large flat surfaces, fast settings. PMAGs (polymer) need different handling.

AR-15 lower / upper receiver (forged 7075 anodized)

Most AR receivers are hard-anodized Type III black. The mark is white aluminum oxide showing through where the laser ablates the dye.

Param	70mm	150mm
Speed	1500-2500 mm/s	1500-2500 mm/s
Power	30-50%	40-65%
Frequency	30-50 kHz	30-50 kHz
Pulse	8-30 ns	8-30 ns
Line interval	0.02 mm	0.025 mm
Loops	1	1

If the mark looks gray instead of crisp white, you're burning through the anodize into the aluminum. Drop power 5%.

Serial number application: read this first

80% lowers / privately-made firearms: do NOT proceed without attorney review

ATF Final Rule 2021R-05F (effective August 2022) materially changed the regulation of unserialized lowers / privately-made firearms (PMFs). The rule was upheld by the Supreme Court in Bondi v. VanDerStok (March 2025, 7-2) and remains in force as of 2026. State-level outright bans on ghost guns / unfinished receivers as of 2026 include Delaware, DC, Illinois, Maryland, Nevada, Oregon, Rhode Island, Vermont, and Washington. Several other states (CA, NY, NJ among others) impose serialization, registration, or transfer requirements without an outright ban. Do not engrave or apply markings to an 80% lower for a customer without first verifying current federal rules and your state's law with an FFL-specialty attorney. The legacy 0.003"/1/16" marking baseline applies to FFL manufacturers/importers; whether and how it applies to your specific work depends on your role and your state.

Reference points (verify current rule text and your role with an attorney before applying):

The long-cited 27 CFR 478.92 marking standard requires minimum 0.003" (0.076 mm) depth and 1/16" (1.6 mm) character height for licensed manufacturers/importers applying identifiers.
Markings are conventionally expected to include the manufacturer name, model, caliber, and serial number (per 27 CFR 478.92(a)(1)(ii) for FFL manufacturers).
State requirements may add character-height, conspicuous-placement, or content restrictions on top of federal rules.

Settings for compliant deep-engraved serial on aluminum receiver (assuming your attorney has confirmed you may legally do this work):

Speed	800 mm/s
Power	90%
Frequency	30 kHz
Pulse	200 ns
Loops	8-12
Line interval	0.02 mm

Verify depth with a depth gauge or pin micrometer on a scrap before applying to the part.

Picatinny rails (6061-T6 aluminum)

Soft, flat, easy. Use the 70mm for fine logos / serials, 150mm for branding across the rail length. Same settings as anodized receiver. The only difference is the rail might be unanodized raw aluminum (gray frosted mark) or anodized (white mark).

For unanodized rails, marking spray (CerMark, TherMark, or equivalent) gives the cleanest black-on-aluminum. Use with full fume extraction. These sprays contain metal-oxide compounds (predominantly molybdenum disulfide / metal-oxide formulations) that should not be inhaled. Mask non-target areas and wipe excess off with the manufacturer's recommended solvent after the engrave.

M-LOK and KeyMod handguards (free-float, aluminum)

M-LOK (developed by Magpul, now the industry-standard attachment pattern) and the older KeyMod system are slot patterns cut into free-float aluminum handguards. The base material is typically 6061-T6 anodized Type II or III black, occasionally FDE / OD-green Cerakote, occasionally raw aluminum on budget tubes. Flat surface area between slot rows gives substantial engrave real estate, more than a traditional Picatinny rail.

Substrate	Engrave behavior	Recipe
Anodized Type II/III black (most modern handguards)	White ablation mark of aluminum oxide showing through dye	Same as anodized receiver above (70mm for detail, 150mm for branding)
Cerakote over anodized (FDE / OD-green / custom)	Ablation through coating reveals the anodized layer or bare aluminum depending on coating thickness	See Cerakote Ablation for full workflow
Raw aluminum (budget tubes)	Faint gray frosted mark; use marking spray for contrast	CerMark / TherMark workflow as for raw Picatinny rails

Thin sections heat up fast

The aluminum between slot rows is often 1.5-2mm thick. Multi-pass deep engrave at high power can heat the tube enough to warp or discolor unevenly across the slot edges. Stay on single-pass surface marking for ablation work on handguards; reserve deep engrave for receiver bodies and rails with more thermal mass underneath.

Common requests: unit insignia, callsigns, names, dates, "DO NOT TOUCH BARREL" caution markings on the inner heat-shield surface. Watch trademark and military-insignia rules (see PMAG Engraving for the framework).

Buffer tube / receiver extension (7075-T6 aluminum)

The receiver extension under the buttstock is 7075-T6 aluminum, typically hard-anodized black, in MIL-SPEC (1.148" / 29.16mm) or commercial (1.168" / 29.67mm) diameter. The curve is gentle but real: a 70mm lens loses focus past about ±5mm off-axis.

Rotary mounting: chuck rotary holds the tube reliably. Tag it as a rotary job in Lightburn (see Fiber Rotary Engraving).
Split-pass strategy without rotary: split the design into 2-3 strips, run each at its own Z height. Tedious but viable for shops without a rotary.
Common subjects: caliber stamp, owner's name, build date, serial-correlating accessory mark.
Watch the threaded end: the castle-nut threads at the rear of the tube can collect engrave debris. Mask before engraving or clean thoroughly after.

Optic housings, mounts, and accessory parts (aluminum, anodized)

Red-dot housings, magnifier mounts, scope rings, and offset optic mounts are typically aluminum (6061 or 7075) with Type III hardcoat anodizing. Engrave settings mirror anodized receiver settings. Common requests are zero-stop documentation, mount-position references, and personal markings.

Optic glass and electronics are NOT engrave-safe

Aluminum housing only. The optical glass, illumination electronics, battery compartments, and any internal lenses on a red-dot or magnified optic are all damaged by 1064nm laser exposure. Mask off all glass surfaces before engraving the housing. Cap the optic on the objective side AND eyepiece side. For optics you're not sure about, remove the optic from any mount and engrave only the bare mount or housing piece, not the assembled optic.

PMAGs (polymer)

Magpul's PMAG is a glass-filled nylon that takes fiber laser marks via pigment bleaching, not ablation. Single-color work is straightforward; multi-color requires a MOPA fiber. For the full deep dive (Q-switched vs MOPA, all PMAG base colors, the multi-pass color-stack technique, jigs, pricing, and the matrix-test workflow), see PMAG Engraving: Lightburn Setup & Color Mastery.

Quick reference starting point on a 30W MOPA + 110mm lens, black PMAG, single-color tan engrave:

Speed	2000-2500 mm/s
Power	20-30%
Frequency	50 kHz
Pulse width	10-30 ns
Line interval	0.04 mm
Loops	1

Settings above produce a light tan / cream mark on black PMAG. Color shade is lot-dependent. Always run a parameter matrix on every new case of mags.

Bolt carrier groups (case-hardened steel)

BCGs are 8620 carburized to ~60 HRC on the surface. You can SURFACE-MARK them but not deep engrave (the case is too hard, and you don't want to compromise it anyway: that's where the wear surfaces are).

Speed	1500 mm/s
Power	50%
Frequency	30 kHz
Pulse	200 ns
Loops	2

Suppressor tubes (titanium / Inconel / stainless)

Cylindrical, requires rotary. Materials vary widely. Test on the brush-finished area first.

Titanium tube: 70mm + chuck rotary, color-anneal settings (see Color Annealing on Stainless / Titanium) for beautiful gradient marks.
Inconel: harder than stainless. Use deep engrave formula at slower speed (500-800 mm/s).
Standard stainless: deep engrave formula directly applicable.

Suppressor compliance: get attorney review before quoting this work

Suppressors are NFA-controlled. Engraving or applying new identifiers to a suppressor generally requires either holding a Type 07 FFL with Class 3 SOT yourself, OR partnering with an SOT who handles the ATF-approved transfer paperwork (typically ATF Form 5 for temporary tax-free movement). Informal "bailment" of a customer's suppressor is NOT a recognized ATF mechanism. Taking possession of a customer's suppressor without proper transfer documentation can constitute an NFA violation. Do not quote suppressor engraving until you've verified your specific compliance path with an NFA-specialty attorney or established SOT.

Pricing

See the consolidated Firearms pricing reference in the Firearms Engraving Primer.

Settings are community-validated starting points, not guarantees. Aluminum alloy and anodizing thickness vary by manufacturer and lot. Federal and state firearms laws current as of 2026; verify ATF compliance and your state's law with an FFL-specialty attorney before publishing services that touch serialized parts or NFA items.