Appearance
A defence contractor manufacturing 155 mm high-explosive projectiles was producing steel shell bodies by hot forging followed by rough machining on conventional lathes. The nose cavity — which houses the fuze and supplementary charge — required a 55 mm × 180 mm concentric bore machined from the projectile base. The existing process used a multi-step boring and reaming operation on a CNC lathe with a cycle time of 22 minutes per cavity and a reject rate of 6 % due to concentricity deviations exceeding 0.1 mm. By replacing the boring operation with a single-pass gun drilling operation using a carbide-tipped drill at 65 m/min cutting speed and 0.06 mm/rev feed, cycle time dropped to 6 minutes, concentricity improved to within 0.03 mm, and rejects fell to 0.5 %. The $800,000 investment in a dedicated deep hole drilling machine was recovered in 14 months through reduced cycle time and scrap. The improved cavity concentricity also eliminated fuze seating issues during assembly, a recurring quality problem that had caused field rejects.
Ammunition Components Requiring Deep Hole Drilling
Deep hole drilling in ammunition manufacturing serves two distinct purposes: creating cavities in projectile bodies for explosive fillers and fuze accommodation, and producing precision bores in fuze components for detonator trains and safety mechanisms.
High-explosive projectile bodies: HE projectiles from 75 mm to 203 mm calibre require a fuze cavity machined into the nose end of the steel body. This cavity receives the fuze assembly and may also contain a supplementary explosive charge. The cavity diameter typically ranges from 30–80 mm with depths of 100–300 mm, depending on projectile calibre and design. The cavity must be precisely concentric with the projectile axis to ensure balanced flight and reliable fuze function.
Mortar shell bodies: Mortar projectiles (60 mm, 81 mm, 120 mm) contain a fuze cavity at the nose and, in some designs, a central bore for ignition train components. The 81 mm M821 HE mortar shell, for example, contains a deep cavity machined from the base, with the fuze pocket at the forward end. These cavities are typically 20–50 mm diameter with length-to-diameter ratios of 4:1 to 10:1.
Armour-piercing projectiles: AP and APDS (armour-piercing discarding sabot) projectiles contain precision-machined internal cavities that must be concentric to within 0.013–0.025 mm. These cavities house the penetrating core or, in the case of APC (armour-piercing capped) rounds, a small explosive filler with a base fuze.
Training and practice projectiles: Inert training rounds often contain a simplified fuze cavity or a through-bore for instrumentation. These are typically lower-cost components but still require controlled drilling processes.
Fuze bodies: Fuze housings — whether nose fuzes, base fuzes, or point-detonating fuzes — contain multiple precision-drilled bores for the detonator train, safety plungers, setback pins, and arming mechanisms. These bores range from 2–15 mm diameter with tight tolerances (H7–H8) and must be burr-free to prevent interference with moving parts.
Supplementary charge containers: Some HE projectile designs include supplementary charge containers that fit into the fuze cavity below the fuze. These containers may be machined from steel or aluminium and require a central bore for the detonator flash channel.
Projectile Body Cavity Drilling Methods
The method used to create the fuze cavity in a projectile body depends on the projectile size, material, heat treatment state, and production volume.
Conventional lathe boring: Smaller production runs and prototype projectiles are often produced by boring the cavity on a CNC lathe. The projectile body is held in a chuck or collet, and a boring bar creates the internal cavity from the base or nose end. This method is flexible but slow, with cycle times of 15–30 minutes for large cavities. Tool deflection can cause concentricity issues, particularly in deep cavities where the boring bar overhang exceeds 4× the bar diameter.
Gun drilling for projectile cavities: Single-pass gun drilling is increasingly used for HE projectile fuze cavities, particularly in medium-to-high volume production. A carbide-tipped gun drill with internal coolant delivery creates the cavity in one pass. The gun drill enters from the projectile base and drills through the solid steel body to create the nose cavity. For existing forged projectile shapes that already have a rough cavity, gun drilling can be used to bring the cavity to final dimensions with superior straightness and concentricity.
BTA drilling for large calibre projectiles: For projectiles above 130 mm calibre, BTA drilling is used for the main cavity. The larger diameter (50–80 mm) and longer cavity depth (200–300 mm) make BTA drilling more efficient than gun drilling due to the higher material removal rate.
Trepanning for material conservation: In large-calibre projectile manufacturing, trepanning can be used to create the fuze cavity while preserving a solid core that may be used for other components. This is less common but relevant for premium projectiles where material cost is significant.
Fuze Body Precision Drilling
Fuze bodies require multiple precision bores that must be machined to exacting tolerances to ensure safety and reliable function. Unlike projectile cavity drilling, fuze drilling involves smaller diameters, tighter tolerances, and complex multi-axis operations.
Detonator pocket drilling: The detonator pocket is a precision bore in the fuze body that houses the primary explosive detonator. Bore diameters range from 4–12 mm with H7 tolerance (0.012–0.018 mm for typical diameters). The bore surface finish must be Ra < 0.8 µm to ensure the detonator assembly seats correctly and the explosive train functions reliably.
Safety mechanism bores: Fuze safety and arming mechanisms require precision-drilled cross-holes and longitudinal bores for setback pins, arming plungers, and locking balls. These bores typically range from 1.5–6 mm diameter with depth-to-diameter ratios of 5:1 to 15:1. The small diameters and tight positional tolerances (0.05–0.1 mm true position) make gun drilling the preferred method.
Flash通道 bores: In-point detonating fuzes, a flash通道 (flash hole) connects the primer to the detonator or the detonator to the booster. This is a small-diameter bore (1–3 mm) that must be straight and free of burrs to ensure reliable flash propagation.
Fuze body threaded bores: Many fuze bodies contain threaded bores for assembly with the projectile body or for attaching the fuze cap. These bores require a precision drilled pilot hole before tapping. The pilot hole must be concentric with the thread pitch diameter axis.
Safety and arming delay mechanism bores: Some fuzes incorporate clockwork or escapement delay mechanisms that require precision-drilled bearing bores and pin holes. These are typically sub-millimetre to 3 mm diameter bores with IT6–IT7 tolerances.
Materials for Ammunition Components
Ammunition components use steels selected for controlled fragmentation, machinability, and ballistic performance.
Projectile body steels:
| Material | Carbon content | Tensile strength (MPa) | Hardness (HB) | Application | Drillability |
|---|---|---|---|---|---|
| AISI 1340 | 0.38–0.43 % | 540–730 | 160–210 | Mortar shells, HE projectiles | Good |
| AISI 1045 | 0.43–0.50 % | 570–700 | 170–220 | HE projectiles, general ordnance | Good |
| AISI 1090 | 0.85–1.0 % | 790–950 | 220–280 | Armour-piercing projectiles | Moderate |
| 4340 | 0.38–0.43 % | 745–1,100 | 220–280 | High-performance ordnance | Moderate |
| HF-1 | Specialised | 800–1,000 | 200–250 | Large-calibre projectiles | Good |
Fuze body materials:
| Material | Application | Characteristics | Drillability |
|---|---|---|---|
| AISI 1215 | Fuze housings (low cost) | Free-machining, 170 HB | Excellent |
| AISI 1144 | Fuze bodies, safety components | Stress-proof, 200–240 HB | Good |
| 7075-T6 aluminium | Lightweight fuze housings | High strength-to-weight | Excellent |
| Brass (C36000) | Fuze components, primer holders | Corrosion-resistant, non-sparking | Excellent |
| PEEK | Training fuze bodies | Lightweight, non-fragmenting | Good |
Material selection considerations:
- AISI 1340 is the standard projectile steel for mortar shells and HE projectiles requiring controlled fragmentation. The manganese content (1.60–1.90 %) improves hardenability and fragmentation characteristics.
- AISI 1045 is used for general-purpose ordnance where fragmentation control is less critical. It offers better machinability than 1340 at the cost of lower strength.
- AISI 1090 provides superior hardness and penetration capability for armour-piercing projectiles but is more difficult to machine and requires carbide tooling.
- For fuze bodies, free-machining steels (AISI 1215, 1144) are common because they produce small, easily evacuated chips during small-diameter drilling, reducing the risk of chip packing.
Gun Drilling Parameters for Projectile Components
AISI 1340 and 1045 ordnance steel (as-forged or normalized, 160–220 HB):
| Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | RPM | Coolant pressure (bar) |
|---|---|---|---|---|
| 10 mm | 50–80 | 0.03–0.06 | 1,600–2,500 | 60–90 |
| 20 mm | 45–70 | 0.04–0.08 | 720–1,100 | 50–80 |
| 30 mm | 40–65 | 0.05–0.10 | 420–690 | 40–70 |
| 40 mm | 35–60 | 0.06–0.12 | 280–480 | 35–60 |
| 50 mm | 30–55 | 0.06–0.14 | 190–350 | 30–50 |
AISI 1090 and hardened ordnance steel (220–280 HB):
| Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | RPM | Coolant pressure (bar) |
|---|---|---|---|---|
| 10 mm | 35–55 | 0.02–0.04 | 1,100–1,750 | 80–120 |
| 20 mm | 30–50 | 0.03–0.05 | 480–800 | 70–100 |
| 30 mm | 25–45 | 0.03–0.06 | 270–480 | 60–90 |
| 40 mm | 22–40 | 0.04–0.07 | 175–320 | 50–80 |
Aluminium and brass fuze components:
| Material | Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | Coolant pressure (bar) |
|---|---|---|---|---|
| 7075-T6 Al | 6 mm | 80–150 | 0.04–0.10 | 20–40 |
| 7075-T6 Al | 12 mm | 70–120 | 0.06–0.14 | 20–35 |
| C36000 brass | 6 mm | 60–120 | 0.04–0.10 | 20–40 |
| C36000 brass | 12 mm | 50–100 | 0.06–0.12 | 20–35 |
Small-diameter fuze bores (1.5–5 mm):
For the small-diameter bores common in fuze safety and arming mechanisms, the following parameters apply for steel fuze bodies:
| Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | RPM | Coolant pressure (bar) |
|---|---|---|---|---|
| 1.5 mm | 25–40 | 0.005–0.015 | 5,300–8,500 | 100–150 |
| 3 mm | 30–50 | 0.008–0.020 | 3,200–5,300 | 80–130 |
| 5 mm | 35–55 | 0.010–0.025 | 2,200–3,500 | 70–110 |
Warning: When gun drilling small-diameter fuze bores below 3 mm, coolant filtration to 10 µm or better is essential. Particles larger than the drill's coolant orifice diameter (typically 0.3–0.5 mm for 3 mm drills) can block coolant flow, leading to rapid tool failure and potential drill breakage inside the component. Consider using a coolant polishing system with magnetic separation for ferrous chips.
BTA Drilling for Large-Calibre Projectile Cavities
For projectile calibres above 130 mm, BTA drilling is the preferred method for creating the fuze cavity.
| Bore diameter | Cutting speed (m/min) | Feed (mm/rev) | RPM | Coolant pressure (bar) | Coolant flow (L/min) |
|---|---|---|---|---|---|
| 40 mm | 35–55 | 0.08–0.16 | 280–440 | 20–35 | 200–350 |
| 50 mm | 30–50 | 0.10–0.18 | 190–320 | 18–30 | 300–450 |
| 60 mm | 28–45 | 0.10–0.20 | 150–240 | 15–28 | 350–550 |
| 80 mm | 25–40 | 0.12–0.22 | 100–160 | 12–22 | 450–700 |
BTA drilling for projectile cavities is typically performed on horizontal BTA machines configured for ordnance work. The Precihole BVN series and similar machines are suitable, offering diameters up to 155 mm with counter-rotation capability for improved straightness.
Heat Treatment Effects on Drilling
The heat treatment state of projectile and fuze components significantly affects drilling parameters and tool selection.
As-forged condition (most common for projectile body drilling): The steel is in a normalized or annealed state with hardness of 160–220 HB. This is the preferred condition for deep hole drilling because the material is soft enough for reasonable tool life but tough enough to produce short, manageable chips. Cutting speeds can be at the upper end of the recommended range.
Spheroidized condition (for controlled fragmentation shells): US Patent 4,246,844 describes a spheroidizing heat treatment for mortar shells where the steel is held at 695 °C ± 10 °C for 12–24 hours to achieve at least 60 % spheroidization of iron carbides. This treatment softens the steel and improves cold formability. In the spheroidized condition, drilling produces longer, stringier chips that require careful coolant flow management. Increase coolant pressure by 15–20 % over the as-forged condition to ensure adequate chip evacuation.
Heat-treated condition (after quenching and tempering): Projectile bodies that are heat-treated before cavity drilling (less common, as drilling is typically performed before heat treatment) present significant challenges. Hardness of 280–350 HB requires reduced cutting speeds (30–40 % below as-forged values) and carbide or CBN tooling.
Stress relief before drilling: Large forged projectile bodies may contain residual stresses that cause the cavity to distort during drilling. A subcritical stress relief anneal at 550–650 °C before drilling reduces distortion and improves cavity concentricity.
Tip: For ammunition production where drilling is performed before heat treatment, always verify the as-forged or normalized hardness of incoming raw material using Brinell or Rockwell testing. Incoming hardness variation of ±20 HB is normal for ordnance steel grades and should be accommodated by running parameters at the conservative end of the range. If hardness exceeds 240 HB for AISI 1340, consider a normalising anneal before drilling.
Machine Configurations for Ammunition Drilling
Ammunition component drilling requires machine configurations that balance precision, production rate, and safety considerations.
Horizontal gun drilling machines: Single-spindle or multi-spindle horizontal gun drilling machines are the standard for HE projectile cavity drilling. Key features for ammunition work include:
- High-pressure coolant systems rated to 150 bar minimum for small-diameter fuze bores
- Chip conveyor systems capable of handling steel chips from ordnance materials
- Through-the-spindle coolant with flow monitoring for drill breakage detection
- Counter-rotation spindle for improved cavity concentricity
- Enclosure with ballistic protection for operator safety
Vertical gun drilling machines: Inverted vertical machines are well-suited for fuze body drilling where workpiece changeover frequency is high. The vertical orientation aids chip evacuation in small-diameter bores and allows gravity-assisted coolant return. Vertical machines are common in fuze manufacturing lines where multiple fuze variants are produced in batches of 500–5,000 units.
Multi-spindle configurations: For high-volume production of standardised projectile bodies (common in 155 mm and 81 mm ammunition), 2–4 spindle gun drilling machines significantly improve throughput. Each spindle operates independently, allowing simultaneous drilling of multiple projectiles. A 4-spindle machine can achieve effective cycle times of 3–5 minutes per projectile for fuze cavity drilling.
CNC lathe with deep hole drilling attachment: Many ammunition manufacturers use existing CNC lathe capacity for projectile cavity drilling by adding a through-coolant drilling attachment with high-pressure coolant booster. This approach is common in lower-volume production where the cost of a dedicated deep hole drilling machine cannot be justified.
Fuze-specific micro-drilling machines: For the small-diameter bores in fuze components, specialised micro-drilling machines with spindle speeds of 10,000–40,000 rpm and sub-micron positioning resolution are used. These machines typically include vision systems for drill alignment and breakage detection.
Quality Requirements for Ammunition Components
Ammunition components are subject to strict quality standards governed by military specifications and safety regulations.
Projectile cavity quality specifications:
| Parameter | Standard ordnance | Precision ordnance |
|---|---|---|
| Cavity diameter tolerance | ±0.1 mm | ±0.05 mm |
| Concentricity to projectile axis | < 0.15 mm | < 0.05 mm |
| Cavity depth tolerance | ±0.5 mm | ±0.25 mm |
| Surface finish Ra (cavity wall) | < 3.2 µm | < 1.6 µm |
| Burr condition | None at thread interface | None at any surface |
Fuze component quality specifications:
| Parameter | Fuze body | Detonator pocket |
|---|---|---|
| Diameter tolerance | H8–H9 | H7 (0.012–0.018 mm) |
| Surface finish Ra | < 1.6 µm | < 0.8 µm |
| True position (cross-holes) | ±0.1 mm | ±0.05 mm |
| Burr condition | None permitted | None permitted |
| Edge break | 0.1–0.3 mm chamfer | 0.1–0.2 mm chamfer |
Inspection methods:
- Air gauging: Bore diameter measurement for fuze detonator pockets (±0.002 mm resolution)
- CMM: Full dimensional inspection of fuze body features, cross-hole positions
- Surface profilometer: Ra and Rz measurement of bore surfaces
- Borescope inspection: Visual check for burrs, tool marks, and surface defects in projectile cavities
- Concentricity gauge: Dial indicator or air-electronic gauging for projectile cavity concentricity
- Thread gauges: Go/no-go verification for fuze cavity threads
- Ultrasonic inspection: Detection of subsurface defects in projectile bodies after drilling
MIL-SPEC compliance: Components manufactured to military specifications such as MIL-F-63446B (fuze assemblies and parts) require:
- No deviation from prescribed dimensions or tolerances without prior approval
- Cumulative tolerance analysis to ensure correct fit and assembly
- Porosity inspection for die-cast fuze bodies
- Jolt and jumble testing per MIL-STD-331 for fuze safety verification
- Lot traceability through the manufacturing process
Tip: For fuze component drilling, implement a 100 % inspection regime for detonator pocket diameter using air gauging with SPC data recording. Unlike projectile cavities where sampling inspection is acceptable, fuze detonator pockets are safety-critical features where a single out-of-tolerance bore can result in a misfire or premature detonation. The cost of 100 % air gauging is negligible compared to the liability of a field failure.
Safety Considerations for Ammunition Drilling
Deep hole drilling of ammunition components involves specific safety considerations beyond those of conventional machining.
Empty shell body drilling: Projectile bodies are machined before filling with explosive. The primary safety consideration is chip management. Steel chips from projectile body drilling are sharp and can cause injury during handling. Chip conveyor systems must be enclosed, and chip collection bins must be emptied regularly.
Drilling near explosive fillers: In some manufacturing processes, cavities are drilled into cast explosive fillers (a method described in US Patent 3,967,527). This is inherently hazardous and has been largely replaced by casting methods that eliminate the need for post-fill drilling. If post-fill drilling is required, it must be performed with:
- Explosion-proof machine enclosures
- Non-sparking tool materials
- Coolant flooding to prevent frictional heating
- Continuous temperature monitoring of the drill and workpiece
- Remote operation from a blast-proof control room
Fuze component safety: Fuze bodies are machined before assembly with explosive components. However, some fuze bodies contain integral primer pockets or flash holes that will later interface with explosives. These features must be deburred and cleaned to prevent any loose material from interfering with the explosive train.
Material handling: Projectile bodies are heavy (20–90 kg for 155 mm shells) and require mechanical handling equipment. Chip removal systems must be positioned to prevent chip accumulation around the workpiece.
Coolant management: Steel drilling produces fine ferrous chips that can contaminate coolant systems. Magnetic separators and paper filters are essential to maintain coolant quality. For ammunition production, coolant should be tested weekly for bacterial growth and tramp oil contamination.
Troubleshooting Ammunition Component Drilling
| Symptom | Likely cause | Correction |
|---|---|---|
| Cavity concentricity > 0.15 mm | Tool deflection or workpiece clamping distortion | Increase guide bush support; reduce feed by 20 %; check clamp alignment |
| Fuze pocket oversize at entry | Worn guide pads on gun drill head | Replace guide pads; verify drill head OD |
| Chip packing in small-diameter fuze bore | Coolant pressure insufficient for chip evacuation | Increase coolant pressure to 100+ bar; verify coolant flow with flow meter |
| Drill breakage in AISI 1090 projectile | Excessive cutting speed causing work hardening | Reduce speed to 25–35 m/min; use AlTiN-coated carbide drill |
| Poor surface finish in projectile cavity | Built-up edge on cutting edge | Increase cutting speed; check coolant concentration; use polished flute drill |
| Fuze detonator pocket eccentric | Drill entry walking on angled surface | Use spot drill or centre drill before gun drilling; increase guide bush length |
| Thread gauge reject on fuze cavity thread | Pilot bore oversize or bell-mouthed | Verify pilot drill diameter; reduce feed at bore entry |
| Chip welding in aluminium fuze body | Coolant lubricity inadequate | Increase coolant concentration to 8–10 %; use oil-based coolant |
| Burr at fuze pocket cross-hole intersection | Drill intersection sequence incorrect | Drill cross-hole before main bore; reduce feed at exit by 50 % |
| Chatter marks in projectile cavity | Long boring bar overhang | Use gun drilling instead of boring; reduce tool overhang; increase dampening |
Frequently Asked Questions
What is the most common deep hole drilling method for HE projectile cavities? Gun drilling is increasingly standard for medium-calibre HE projectiles (75–130 mm) where the fuze cavity diameter is 30–55 mm. BTA drilling is used for larger cavities above 50 mm in large-calibre projectiles (155 mm+). Traditional lathe boring is still used for low-volume production.
What materials are used for projectile bodies that require deep hole drilling? AISI 1340 is the standard material for mortar shells and HE projectiles requiring controlled fragmentation. AISI 1045 is used for general-purpose ordnance, and AISI 1090 for armour-piercing projectiles. Alloy steels such as 4340 are specified for high-performance ordnance.
What are the typical tolerances for fuze detonator pockets? Fuze detonator pockets require H7 tolerance (0.012–0.018 mm for 6–10 mm diameter bores) with surface finish Ra < 0.8 µm. These are among the tightest tolerances in ammunition component machining.
How does heat treatment affect projectile cavity drilling? Projectile bodies are typically drilled in the as-forged or normalized condition (160–220 HB). Spheroidized material produces longer chips requiring higher coolant pressure. Drilling after heat treatment (280+ HB) requires reduced cutting speeds and carbide tooling.
What coolant pressure is required for drilling fuze components? Small-diameter fuze bores (1.5–5 mm) require 70–150 bar coolant pressure, with the highest pressures needed for the smallest diameters. Coolant filtration to 10 µm is essential to prevent drill blockage.
Can projectile cavities be drilled on a standard CNC lathe? Yes, using through-coolant drilling adaptors with high-pressure coolant boosters. This is common in lower-volume production but cycle times are typically 3–4× longer than dedicated gun drilling machines.
What safety considerations apply to ammunition component deep hole drilling? Projectile bodies are machined before explosive filling, so normal machining safety applies (chip handling, coolant management). Post-fill cavity drilling is hazardous and has been largely replaced by casting methods. Fuze components require scrupulous deburring to prevent interference with explosive trains.
What inspection methods are used for fuze detonator pockets? Air gauging (±0.002 mm resolution) is standard for 100 % inspection of detonator pocket diameter. CMM is used for cross-hole position verification, and borescope inspection verifies internal surface condition and burr freedom.
How does ammunition component drilling differ from gun barrel drilling? Projectile cavity drilling involves shorter bores (100–300 mm depth vs 1,000–6,000 mm for gun barrels) with larger diameters relative to length. The emphasis is on cavity concentricity and thread interface quality rather than the extreme straightness and surface finish required for rifled gun barrels. Fuze component drilling involves small-diameter precision bores with IT6–IT7 tolerances that are more comparable to aerospace hydraulic component drilling.
What is the typical production volume for ammunition deep hole drilling? Military ammunition production runs range from 5,000–100,000+ units per year per calibre for major NATO-standard calibres (155 mm, 81 mm, 120 mm). Fuze production volumes are higher, as multiple fuzes may be produced for each projectile. High-volume production favours multi-spindle gun drilling machines while lower volumes use CNC lathe attachments.
Summary
| Aspect | Projectile fuze cavities | Fuze detonator pockets | Fuze safety mechanism bores |
|---|---|---|---|
| Typical bore diameter | 30–80 mm | 4–12 mm | 1.5–6 mm |
| Typical depth | 100–300 mm | 10–40 mm | 10–80 mm |
| Drilling method | Gun drilling or BTA | Gun drilling (micro) | Gun drilling (micro) |
| Typical material | AISI 1340, 1045, 1090 | AISI 1215, 1144, brass | AISI 1144, 7075 Al |
| Cutting speed | 25–80 m/min | 25–55 m/min | 25–50 m/min |
| Feed | 0.03–0.14 mm/rev | 0.005–0.025 mm/rev | 0.005–0.020 mm/rev |
| Coolant pressure | 30–90 bar | 80–150 bar | 70–150 bar |
| Concentricity requirement | < 0.05–0.15 mm | < 0.05 mm (true position) | < 0.1 mm (true position) |
| Surface finish Ra | < 1.6–3.2 µm | < 0.8 µm | < 1.6 µm |
| Inspection method | CMM, concentricity gauge | Air gauging, CMM | CMM, borescope |
Ammunition projectile and fuze deep hole drilling encompasses two distinct but related applications: the creation of fuze cavities in projectile bodies and the precision drilling of fuze components. Projectile cavity drilling uses gun drilling and BTA methods on medium-to-large diameter bores in ordnance steels (AISI 1340, 1045, 1090), typically performed before heat treatment in the as-forged condition. Fuze component drilling involves small-diameter precision bores in free-machining steels and non-ferrous materials, requiring high spindle speeds, high coolant pressure, and micron-level tolerances. Both applications demand strict quality control, with fuze detonator pockets requiring H7 tolerances and 100 % air gauging inspection. As global defence spending continues at elevated levels and ammunition stockpiles require replenishment, the demand for efficient, high-precision deep hole drilling in ammunition manufacturing will remain strong — favouring dedicated gun drilling and BTA machine configurations with automated workpiece handling and integrated inspection.