Build Path C — From Scratch

Contents

(Generated by build/inject_toc.py at build time. Section headers below are the source of truth.)

This is the lab volume. Per _shared/deep_dive_protocol.md § 4, build-from-scratch is one of the two mandatory volumes in every firearms deep dive in this hub, and the standard for this hub is first-class machinist treatment — not the hand-wave most prop guides give the from-scratch path. That standard applies here: the from-scratch E-11 is treated as a real fabrication project executable in a real lab.

The premise behind the standard is the hub-level lab capability laid out in ../../CLAUDE.md: multiple CNC machines, multiple 3D printers, a 100 W large-format laser, a full gunsmithing toolset, and the experienced firearms / gunsmithing background to do action work and fitting correctly. For the E-11 specifically, the load-bearing fabrication challenge is the Sterling-pattern receiver tube — a wrapped-and-welded sheet-steel cylinder with a helical cooling-hole pattern. Everything else (fire-control housing, folding stock, greeblies, magazine) is either standard machine-shop work or 3D-printing work. The receiver is the project’s center of gravity.

Caveat on lab catalog specifics. The lab capability catalog at ../../_shared/lab_capability.md is TBD as of this volume’s authoring. Specific machine models, travels, spindle capabilities, sheet-metal handling capacities, welder specifications, and printer build volumes are not committed to in this volume. Where a specific capability matters, this volume describes the capability requirement; matching that to the actual lab is the implementation-time decision. Ask before assuming any specific capability — the hub rule.

6.1 Overview — the four work packages

A from-scratch E-11 build naturally divides into four work packages:

Package	Component	Effort	Lab capability needed
1. Receiver tube	The Sterling-pattern wrapped + welded sheet-steel cylinder	40–80 hr	Sheet-metal forming + TIG welding + drilling fixture / CNC drill
2. Fire-control housing	The lower receiver / pistol grip / magazine well / trigger group	30–60 hr	CNC mill (or sheet-aluminum welding)
3. Stock + magazine	Folding wire stock + curved 34-rd magazine	15–25 hr	Wire / rod bending + welding; sheet-metal pressing or 3D-printing
4. Greeblies	Scope rail + scope pod + M38 tube + Hengstler counter + Sandtrooper additions	15–35 hr	CNC mill + 3D printer + laser engraver

Plus an integration pass (assembly, fitting, finish, weathering): 10–30 hr.

Total honest estimate: 100–250 hours of bench time spread across the four packages. The wide range reflects whether the build is one-off (slow) or part of a repeating-pattern run where fixtures get re-used. The deep end of the range assumes building the receiver tube with custom rotary-CNC fixturing for the cooling-hole pattern; the shallow end assumes a manual drill jig and accepting more variance in the cooling-hole placement.

Decision to make before starting: is this build firing or non-firing? A non-firing build skips the fire-control internals (semi-auto sear, disconnector, working trigger) and the barrel-and-chamber work. A firing build is a semi-auto rifle that needs all of those — and a barrel that headspaces correctly in 9×19, which is its own fabrication challenge. Vol 6 assumes the non-firing path as the default (faster, no manufacture-for-self legal posture, no headspacing); § 6.9 covers what changes for a firing build.

6.2 Work package 1 — The receiver tube

The Sterling-pattern receiver is a wrapped + welded sheet-steel cylinder with the following key dimensions (from Vol 3 § 3.4):

• Length: ~197 mm (7.75″)
• OD: ~38 mm (1.5″)
• Wall: ~2 mm
• Helical cooling-hole pattern: 6 helical rows, ~28 holes total
• Fire-control housing mounting features on the underside

6.2.1 Material selection

The original Sterling spec was 4130 steel (chrome-molybdenum, the standard receiver-grade alloy steel). 4130 is the right choice if you have the welding and finishing setup to manage it.

For a build that just needs to look right and survive trooping handling, 1018 mild steel is acceptable — much easier to weld, much cheaper. The non-firing-build context (this volume’s default) makes 1018 a reasonable choice; the receiver doesn’t see chamber pressure.

Sheet stock dimension: ~140 mm × 200 mm × 2 mm sheet (length covers the receiver + scrap for handling; width covers the unwrapped circumference of the cylinder ≈ π × 38 = 119 mm + lap allowance).

6.2.2 Forming the cylinder

Three approaches, in order of fabrication-shop sophistication:

Option A — Sheet-roller forming. A small slip-roll (manual or powered) wraps the flat sheet into a cylinder. The seam runs longitudinally. This is the cleanest method and produces the truest cylinder; it requires a slip-roll capable of handling 2 mm steel.

Option B — Press-form with a mandrel. Cut the flat blank; bend the longitudinal edges over a mandrel using a press brake or hand-bend tooling; close the seam progressively until the edges meet. More forgiving than slip-rolling but produces a less-true cylinder; some hand-work is needed to true it up.

Option C — Source pre-formed tube. Drawn or seamless steel tubing in the right OD (~38 mm) and wall (2 mm) is commercially available (look for thin-wall DOM tubing or specialty seamed structural tubing). This skips the forming step entirely — buy a length of tube, cut to length, and proceed to the cooling-hole-pattern drill. The trade-off: a sourced tube is a different microstructure than a wrapped sheet (DOM tubing has the seam already welded by the manufacturer), and the seam is internal and may be slightly thicker than the wall — typically fine for non-firing.

For most labs, Option C is the right answer — sourced tube, cut to length, skip the wrap-and-weld step. Reserve Option A or B for builds where authentic-reproduction of the Sterling’s manufacturing method is part of the project.

6.2.3 Welding the seam (if formed from sheet)

If Option A or B was chosen, the longitudinal seam needs welding. TIG welding is the right choice — narrow heat-affected zone, clean weld bead, manageable distortion. MIG can be used but produces a wider HAZ and may require more cleanup. Aim for full-penetration weld with minimal external bead height; the receiver’s external surface needs to read smooth, not “welded together.”

After welding: stress-relieve (low-temperature post-weld treatment if 4130) and dress the weld bead flush with the external surface. A small belt-sander, then progressive abrasive finishing, brings the seam down to the surrounding sheet surface.

If Option C was chosen (sourced tube), this section is irrelevant.

6.2.4 Drilling the helical cooling-hole pattern

This is the receiver’s signature feature — six helical rows of cooling holes running diagonally along the receiver length. The original Sterling pattern is:

• 6 helical rows
• ~28 holes total
• Hole diameter ~6 mm (1/4″)
• Helix angle ~10–15° from the receiver axis
• Holes axially-aligned in rows but staggered between adjacent rows for the helical look

Three approaches:

Approach A — Rotary CNC drilling. Set up the receiver tube in a rotary indexer on the CNC mill. Program a G-code path that rotates the tube and indexes it longitudinally between holes. The mill’s drilling cycle handles each hole. This produces a dead-accurate helical pattern and is the right approach for a builder doing multiple receivers (the fixture gets reused).

Approach B — Manual drill jig. Build a sheet-metal jig that wraps the tube and has the hole pattern marked at the correct positions. Drill through the jig with a hand drill or drill press, one hole at a time. Cheaper and faster for a one-off but less precise — expect ±1–2 mm placement variance from hole to hole.

Approach C — Hybrid: laser-cut jig + manual drilling. Use the 100 W laser to cut a sheet-metal wrap-around jig with the hole pattern, wrap it around the tube, and drill through the jig. The jig is dimensionally accurate (laser cut), the drilling is manual (slow but acceptable for one-off). This is the right approach for most labs.

Deburr the holes inside and out after drilling. Holes that have raised burrs around their edges will be visible from external photography even after finishing.

6.2.5 Fire-control housing mounting features

The Sterling fire-control housing attaches to the receiver via two threaded posts on the underside of the receiver. These need to be added before finishing.

Approaches:

• Weld on bosses — short cylindrical bosses, threaded, welded to the underside of the receiver at the correct positions. Position from the Sterling factory drawings (Vol 7 has the dim sheet); position tolerance is critical (the fire-control housing must mate cleanly).
• Sheet metal tabs — cut tabs into the receiver bottom; bend down; tap. Less authentic but adequate.

For a non-firing build, exact tolerance on the mounting feature positions is less critical (the housing doesn’t need to hold under firing stress); for a firing build, exact tolerance matters.

6.3 Work package 2 — The fire-control housing

The Sterling fire-control housing is the lower receiver: pistol grip, trigger group, magazine well, and the upper-receiver attachment lugs. On the original Sterling it is cast aluminum.

Two fabrication options for a from-scratch build:

6.3.1 Option A — CNC mill from billet

The cleanest path for a lab with a capable CNC mill. Stock: a billet of 6061-T6 or 7075-T6 aluminum, sized to the bounding-box of the housing (~150 mm × 80 mm × 60 mm rough).

Op sequence:

1. Op 1 — Profile-mill the exterior. Set up the billet on parallels in a vise; profile-mill the outside contour with a square endmill. Leave the magazine-well area solid (Op 3 will hollow it).
2. Op 2 — Drill / mill the receiver-attachment lug pattern. Match the receiver’s mounting posts (§ 6.2.5).
3. Op 3 — Pocket the magazine well. Plunge-mill the magazine well from the bottom of the housing; clean up with a 1/4″ endmill. Tolerance to the Sterling magazine is ±0.2 mm.
4. Op 4 — Mill the trigger-group pocket. Hollow out the pocket where the trigger group sits; drill the trigger-pin and hammer-pin holes.
5. Op 5 — Finish-mill the pistol grip profile. The grip is part of the housing on the Sterling; mill the contour from the same billet.
6. Op 6 — Final surface finish. Tumble or media-blast the exterior to a uniform matte aluminum finish (will be parkerized or Cerakoted later).

Time: 20–30 hours for a careful one-off with proper fixturing.

6.3.2 Option B — Weld up from sheet aluminum

For a lab without large billet capacity, an alternative is to weld up the housing from sheet aluminum panels. Less authentic-looking; requires TIG welding of aluminum.

This is the option for builds where billet machining isn’t on the table. Quality varies with the welder’s skill; not the recommended path for a hero-spec build.

6.3.3 Trigger group decisions

For a non-firing build: machine cosmetic-only trigger group parts. Trigger, hammer, sear can be aluminum shapes that fit the housing pockets but don’t function. Skip the disconnector and the bolt-hold-open.

For a firing build: the trigger group must function with a semi-auto closed-bolt sear arrangement (per the Path A1 / A2 discussion in Vol 4). Open-bolt operation is not legal under post-1982 ATF guidance. The semi-auto sear is its own machining project — typically machined from 4140 or O-1 tool steel, hardened, ground to finish. This pushes Vol 6’s effort estimate to the upper end (200–250 hr).

For the default (non-firing) build: ignore § 6.3.3 entirely. The trigger group is cosmetic.

6.4 Work package 3 — Folding stock and magazine

6.4.1 The folding wire stock

The Sterling folding stock is bent steel rod with a hinged butt-plate. Construction options:

• Bend from rod stock. ~10 mm round-steel rod, bent over a forming jig in two passes (first the long shaft, then the butt-plate cross-piece). Weld the cross-piece to the shaft. Hinge mounts to the receiver via a steel collar at the front end. This is the right path for a lab with rod-bending capacity.
• 3D-print + reinforce. Print a one-piece stock in a high-strength filament (PA-CF nylon-carbon, or PETG-CF), reinforce internally with steel rod inserts at high-stress points. Less authentic feel; works for non-firing display builds.

The hinge mechanism — a steel pin running through a tab on the receiver — needs to allow the stock to fold flat against the left side of the receiver and lock in the extended position. Tolerance: ±0.5 mm in pivot-pin fit.

6.4.2 The curved 34-round magazine

For a non-firing build the magazine is purely cosmetic and can be:

• 3D-printed (PETG or ABS) in two halves and glued.
• Sheet-metal pressed — cut the side panels from sheet steel, press-form the curve, weld together. More authentic; more work.
• Sourced from a parts kit — a real Sterling magazine body (de-internalled if needed) acquired from a parts-kit vendor; finish to match.

For a firing build, the magazine must function as an actual feed device — get a real Sterling magazine, period. Fabricating a functional 34-round curved feed magazine is its own fabrication project and is not in scope for this volume.

6.5 Work package 4 — Greeblies

Vol 7 covers each greeblie at sub-assembly depth. This section is the fabrication-path summary:

• Scope rail — CNC mill from aluminum bar. Dimensions per Vol 7 § 7.2. Drill the scope-pod and M38-tube mounting holes during the same setup.
• Scope pod — 3D-print (SLA / resin preferred for surface finish), or CNC-turn from aluminum (more authentic; harder). The hero pieces are believed to be CNC-turned from solid. Vol 7 § 7.3 covers.
• M38 grenade-launcher tube — CNC-turn on a lathe (the right approach if you have a lathe) or 3D-print (acceptable for non-load-bearing prop use). Vol 7 § 7.4 covers.
• Hengstler counter (optional) — 3D-print (SLA for fine detail). Vol 7 § 7.5 covers.
• Sandtrooper T-track (Sandtrooper only) — laser-cut from sheet steel, bent into the T-profile, welded. Vol 7 § 7.6 covers.
• Sandtrooper ammo pouch (Sandtrooper only) — sewn from canvas / leather. Not a machining project.

Total greeblie fabrication: 15–35 hours depending on the mix of CNC vs 3D-print and the scope-pod complexity.

6.6 Op sequence — the recommended build order

A from-scratch E-11 build is best executed in this order:

1. CAD the whole prop first. Don’t start fabrication until the whole assembly has been modeled in Fusion 360 / SolidWorks. Receiver + fire-control housing + greeblies — all dimensioned, all mating features verified. This catches mistakes before they become metal.
2. Fabricate the receiver tube — Work package 1. This is the long pole; get it done first so the rest fits to it.
3. Fabricate the fire-control housing — Work package 2. Fit-up to the receiver mounting features before final-finish.
4. Fabricate the folding stock + magazine — Work package 3.
5. Fabricate the greeblies — Work package 4. CNC-mill the scope rail; turn or print the scope pod and M38 tube.
6. Test-fit the whole assembly — bare metal, no finish. Verify the magazine fits, the stock folds, the greeblies sit at the right angles. Adjust as needed.
7. Disassemble for finishing. Parkerize (or Cerakote) each component separately.
8. Weather pass. Drybrush, chipping, dust patina per Vol 8.
9. Final assembly. Reattach greeblies, install magazine, mount stock.
10. 501st CRL pass. Check proportions and finish against the target CRL (Stormtrooper, Sandtrooper, Death Star Trooper).

6.7 Tolerances and fitting

The Sterling pattern is forgiving — the gun was designed for wartime mass production, not bench-rest precision. Reasonable fitting tolerances:

Mating feature	Tolerance
Fire-control housing to receiver	±0.2 mm in position; the lugs need to engage cleanly
Magazine to magazine well	±0.2 mm in lateral; ±15° angle is correct
Folding stock pivot	±0.5 mm in pivot-pin fit; allows folding without binding
Scope rail to receiver	±0.5 mm in mounting-hole position
Greeblie-to-rail mounting	±1 mm; mostly cosmetic
Cooling-hole pattern	±1–2 mm hole-to-hole placement (depends on drilling method)

For a non-firing build these tolerances are forgiving. For a firing build the trigger-group tolerances (sear engagement, disconnector reset, hammer-pin position) tighten substantially — those are gunsmithing tolerances, not prop-build tolerances.

6.8 Honest difficulty assessment

A from-scratch E-11 is harder than a Doopydoo build (obviously) but easier than a from-scratch Mauser C96. The Sterling pattern was designed to be cheap and easy to make — wartime sheet-metal fabrication with minimal precision machining. The from-scratch C96 (per ../Mauser_C96/02-inputs/volume_sources/vol9.md) has a screwless lockwork that is genuinely difficult to fit. The Sterling has no equivalent — its fire-control is conventional and forgiving.

The hard parts of a from-scratch E-11 are:

• The receiver tube fabrication — getting the cylinder true and the cooling-hole pattern accurate. The lab needs sheet-metal capability (or a sourced tube) and a drilling approach that doesn’t wander.
• The fire-control housing pocketing — for the billet-machined approach, hollow pocketing of the magazine well and trigger pocket is multi-op CNC work.
• The scope pod CNC turning — if going for authentic-reproduction (rather than 3D-printed substitute), turning the pod from solid stock at correct dimensions is delicate work.

Compared to the Mauser_C96 from-scratch volume’s 100–300+ hour difficulty estimate, the Sterling-pattern E-11 is in the 100–250 hour range. This volume is the second-most-achievable from-scratch build in this hub (with the STEN, when scaffolded, being the easiest by design — see the STEN queue entry in ../../CLAUDE.md).

6.9 Legal posture — manufacture for self (semi-auto only)

A from-scratch firing E-11 is a semi-auto rifle manufactured for self under US federal law. The federal posture is:

• No registration is required to manufacture a Title I semi-auto rifle for personal use (this is established under the GCA and reaffirmed in ATF guidance).
• State-level serialization is increasingly required. California (since 2018) requires state-issued serial numbers on home-built firearms. Other states are following.
• The receiver must be marked. Federal law requires the receiver bear a unique mark identifying the manufacturer; for home-built, the maker is the manufacturer. Most builders mark their initials + a serial number; some states require additional information (state-issued serial, build date).
• The rifle must be semi-auto. Open-bolt operation is “readily convertible” to full-auto under post-1982 ATF guidance and is not legal for a from-scratch build. The semi-auto sear arrangement is mandatory.
• 922(r) compliance does not apply if all parts are US-made (which they are, in a from-scratch build) — 922(r) only applies to builds with imported parts.

For a non-firing from-scratch E-11 (this volume’s default), federal posture is simpler:

• It is not a firearm under federal law — no chamber, no firing pin, no functional action. 27 CFR § 478.11 firearm definition is not met.
• It may be regulated as an “imitation firearm” under 15 USC § 5001 (Toy Gun Marking Act) — the orange-tip rule may apply depending on the configuration. Many builders include a removable orange tip or omit it entirely after consulting state law.
• State imitation-firearm laws apply as for any non-firing replica. Vol 10 § 10.5 has the state-by-state matrix.

Vol 10 § 10.6 has the full posture for from-scratch / manufacture-for-self builds.

6.10 What this volume is not

• Not a firing-rifle gunsmithing manual. Semi-auto sear design, headspacing a 9×19 chamber, and the broader gunsmithing of a from-scratch rifle are in the gunsmithing literature; this volume covers the prop-fabrication side. Section 6.9 flags where the firing path diverges.
• Not a Sterling-action restoration manual. A real Sterling needing rebuild is in the gunsmithing literature (some of it is in the Hobart and Walter references in Vol 12).
• Not a CAD-model walkthrough. The CAD step in § 6.6.1 is mandatory but the modeling itself is left to the builder.
• Not lab-catalog-specific. Lab capability is treated as a load-bearing input; specific machine claims (mill model, sheet-metal-roll capacity, etc.) are deferred to the lab catalog at ../../_shared/lab_capability.md (TBD).
• Not a 501st CRL substitute. The CRL is the trooping spec; this volume produces a prop that meets the CRL when built carefully.

6.11 References (Vol 6)

• Vol 3 — Donor Firearm Provenance — Sterling Mk 4 / L2A3 — the dimension specification this build targets.
• Vol 7 — Sub-Assemblies & Greeblies — depth treatment of every greeblie machining detail.
• Vol 8 — Materials & Finishing — parkerizing, Cerakote, weathering recipes.
• Vol 10 — Legal & Regulatory Posture — manufacture-for-self posture (§ 10.6) and state imitation-firearm laws (§ 10.5).
• ../DEVELOPMENT.md — fabrication workflow overview, sub-assembly breakdown.
• ../../_shared/lab_capability.md (TBD) — specific lab tooling catalog to be populated.
• ../../Mauser_C96/02-inputs/volume_sources/vol9.md — sibling from-scratch volume for the Mauser C96; cross-reference for the hub’s machinist-grade authoring standard.
• Hobart, F.W.A. The Sterling Story. Sterling Engineering Co., 1995 — Sterling history and engineering background.
• Walter, John. The Sterling Sub-Machine Gun. (Small Arms Profile 12.) Profile Publications, 1971 — period reference with Sterling factory drawings.
• ATF Open Letters / Determination Letters — semi-auto sear configuration, open-bolt-versus-closed-bolt guidance.
• 27 CFR § 478 — Federal firearms regulations under the Gun Control Act.
• 15 USC § 5001 — Toy Gun Marking Act / imitation firearm requirements.
• Full bibliography consolidated in Vol 12.