Deep Hole Drilling: Armored Vehicles, Naval Guns & Missiles

Deep hole drilling was born from the need for accurate gun barrels. The term "gun drilling" is not metaphorical — the first single-lip drilling tools were developed specifically for creating straight, true bores in rifle and cannon barrels. Two centuries later, the defense industry remains the most demanding customer for deep hole drilling technology.

Deep hole drilling serves defense manufacturing across three primary domains: gun barrels and ordnance (the historical core), armored vehicle components, and missile and aerospace defence components. Each domain imposes specific requirements on the drilling process — from the extreme straightness demanded by cannon barrels to the material challenges of high-hardness armored steels.

Historical Context ​

The relationship between deep hole drilling and defense is as old as the technology itself.

The BTA (Boring and Trepanning Association) system, developed in 1943 to meet wartime demand for cannon barrels, was the first internal chip evacuation method for deep hole drilling. It allowed higher penetration rates and better hole quality than external chip removal methods, becoming the standard for large-calibre ordnance manufacturing.

Gun Barrel and Ordnance Manufacturing ​

Small Arms Barrels ​

Small arms barrels (pistols, rifles, machine guns) are manufactured using gun drilling as the first operation after gun drilling the initial bore:

Process sequence for a rifle barrel:

1. Gun drilling: The initial bore is drilled from solid bar stock, typically 5–20 mm diameter at depth ratios of 50:1 to 100:1
2. Reaming: The gun-drilled bore is reamed to final diameter with improved surface finish
3. Rifling: Button rifling or cut rifling creates the spiral grooves that impart spin to the projectile
4. Chambering: The breech end is machined to accept the cartridge
5. Honing: Final bore finishing for accuracy and consistency

Cannon and Artillery Barrels ​

Large-calibre barrels (20 mm to 200 mm) use BTA drilling as the primary bore creation method:

Process sequence for a cannon barrel:

1. BTA drilling: The initial bore is drilled from solid forged or bar stock, typically 20–200 mm diameter at depth ratios of 30:1 to 60:1
2. Trepanning (optional): For very large diameters, trepanning removes a solid core that can be repurposed
3. UNS reaming: Precision reaming of the BTA-drilled bore to final dimensions
4. Rifling: Servo-driven button rifling for calibers up to 200 mm
5. Honing and inspection: Final surface finishing and ballistic inspection

UNISIG's defense-grade machines are capable of BTA drilling up to 630 mm diameter and 20,000 mm depth, with dedicated servo-driven rifling machines for calibers from .17 to 200 mm.

Naval Gun Systems ​

Naval gun barrels — such as the BAE Systems Mk 45 5-inch (127 mm) naval gun — require the same fundamental deep hole drilling process scaled to large dimensions. The Mk 45 Mod 4 upgrade includes a 62-caliber barrel (barrel length = 62 × 127 mm = 7,874 mm) with mechanically strengthened gun mount.

The U.S. Navy's NAVSUP Weapon Systems Support solicited 655 automatic gun barrels in FY2024–2025 (Solicitation N0010425RQA74), indicating sustained demand for deep hole drilling in naval ordnance.

Armored Vehicle Components ​

Track Shoes ​

Armored vehicle track shoes (the individual links that form the continuous track of a tank or armoured personnel carrier) require deep hole drilling for the pin bores that connect adjacent links. The challenges include:

• Material: High-hardness armored steels (350–550 HB)
• Hole geometry: Cross-holes at precise spacing for track pin assembly
• Production volume: Hundreds of track shoes per vehicle, thousands per production run
• Portable drilling: Field maintenance requires modular deep hole drilling systems for track repair and modification

Precihole Machine Tools lists track shoes as a primary defense application for its deep hole drilling machines.

Hydraulic and Suspension Systems ​

Armored vehicles use hydraulic systems for steering, suspension, and weapons elevation. These systems require deep hole drilling for:

• Hydraulic cylinders: BTA-drilled tubes for recoil mechanisms and suspension dampers
• Valve blocks: Gun-drilled oil passages in high-strength steel manifolds
• Piston rods: Deep-drilled axial bores for lightweight hydraulic actuators

The combination of high-strength materials (often 300M or similar high-alloy steels) and deep depth ratios makes these components particularly demanding for deep hole drilling.

Structural Components ​

Armored vehicle structural components — including torsion bar housings, drive sprocket shafts, and idler wheel assemblies — require deep hole drilling for weight reduction, oil passages, or assembly features. The key challenge is machining hardened armored steels (often 400–550 HB) that dull conventional tooling rapidly.

Tip: For deep hole drilling in armored steels, carbide gun drills with AlTiN or TiSiN coatings are recommended. Feed rates should be reduced by 30–50% compared to standard alloy steels of equivalent hardness, and coolant pressure should be increased to ensure chip evacuation from the longer chip-forming zone.

Missile and Aerospace Defense Components ​

Missile systems require deep hole drilling for components where precision, weight reduction, and reliability are critical:

Missile Components Requiring Deep Hole Drilling ​

Certification Requirements ​

Defense deep hole drilling contractors must maintain rigorous certifications:

Hunting Dearborn (Fryeburg, Maine) exemplifies the certification profile of a defense deep hole drilling contractor: AS9100D, ISO 9001, ITAR registered, NADCAP accredited, DDTC licensed, and CAGE coded.

Equipment Used in Defense Deep Hole Drilling ​

Machine Types ​

Key Suppliers to the Defense Sector ​

Automation in Defense Deep Hole Drilling ​

Defense manufacturing increasingly demands automation for both production efficiency and quality consistency. Precihole has integrated robotic loading and unloading systems from Fanuc, Mitsubishi, ABB, Kuka, and Yaskawa for firearm barrel production, enabling lights-out manufacturing for 24/7 unattended operation.

Automation is particularly valuable for high-volume defense components:

• Small arms barrels: Robotic loading of barrel blanks into gun drilling machines, automatic tool wear compensation
• Track shoes: Automated transfer between drilling stations with in-process gaging
• Missile components: Robotic part handling for multi-operation workcells combining drilling, boring, and inspection

Warning: Automation in defense deep hole drilling requires careful consideration of security requirements. ITAR-controlled parts may not be viewable by remote monitoring systems, and data transmission for Industry 4.0 diagnostics must comply with defense security protocols. Discuss these requirements with the machine builder before specifying remote access capabilities.

FAQ ​

What is the difference between gun drilling and BTA drilling in defense applications? ​

Gun drilling (external chip removal) is used for small-diameter precision bores typical of small arms barrels (5–20 mm diameter, depth ratios up to 100:1). BTA drilling (internal chip removal) handles larger diameters (20–630 mm) at higher penetration rates, making it the standard for cannon and artillery barrels. The BTA system was developed specifically for defense applications during WWII.

Which defense components require deep hole drilling? ​

Gun barrels (small arms through naval cannons), armored vehicle track shoes, hydraulic cylinders for steering and suspension, missile fuel injector bodies, rocket motor tubes, guidance system housings, launch tube components, periscope tubes, radar masts, and submarine components all require deep hole drilling.

What certifications are required for defense deep hole drilling contractors? ​

ITAR registration is mandatory for US defense contractors. AS9100D or AS9100C (aerospace and defense quality management) is typically required. NADCAP accreditation for special processes, DDTC licensing for export-controlled work, and SAM.GOV registration for US federal contracts are also common requirements. Many contracts also require customer-specific quality approvals (e.g., Naval Submarine approval).

What materials are most challenging for deep hole drilling in defense applications? ​

High-hardness armored steels (400–550 HB) are the most challenging due to rapid tool wear and difficulty maintaining chip form. Titanium alloys (used in missile and aerospace defense components) create built-up edge at conventional speeds. High-strength steels like 300M combine high hardness with low thermal conductivity, concentrating heat at the cutting edge. Nickel-based superalloys (Inconel 718) used in missile components work-harden during machining.

How deep can defense deep hole drilling machines drill? ​

UNISIG's BTA machines can drill up to 20,000 mm (20 metres) depth with diameters up to 630 mm. Small arms gun drilling typically reaches 500–1,500 mm depth. Naval gun barrels such as the Mk 45 5-inch (127 mm) gun have barrels approximately 7,900 mm (62 calibers) long. Cannon barrels typically range from 3,000–8,000 mm depending on caliber and platform.

What is the process sequence for manufacturing a cannon barrel? ​

A typical cannon barrel manufacturing sequence is: (1) BTA drilling from solid forged stock, (2) trepanning if material conservation is required, (3) UNR reaming for diameter and surface finish, (4) servo-driven button rifling to cut the spiral grooves, (5) honing for final bore surface finish, and (6) ballistic inspection including bore-scope examination and dimensional verification.

Who are the major defense contractors offering deep hole drilling services? ​

Hunting Dearborn (Fryeburg, ME), Applied Aerospace & Defense, Grand Valley Manufacturing, Perfect Bore Manufacturing (UK), and Mollart Engineering (UK) are established defense subcontractors with deep hole drilling capabilities. UNISIG and Precihole manufacture deep hole drilling machines used by defense contractors and in-house defense manufacturing operations.

How is automation being applied to defense deep hole drilling? ​

Robotic loading and unloading of parts, automatic tool wear compensation, in-process gaging, and lights-out manufacturing capabilities are being deployed for high-volume defense components such as small arms barrels and track shoes. Precihole has integrated robots from Fanuc, Mitsubishi, ABB, Kuka, and Yaskawa into their deep hole drilling systems. However, automation must account for ITAR security requirements that may restrict remote monitoring and data transmission.

Summary ​