What is Gun Drilling?
Gun drilling is a precision deep hole drilling process that uses a single-lip cutting tool with internal coolant delivery to produce holes with exceptionally high depth-to-diameter ratios. Originally developed over 100 years ago for manufacturing gun barrels, gun drilling can achieve holes up to 300 times the drill diameter in depth while maintaining tight tolerances and excellent surface finish in a single pass.
Unlike conventional twist drilling—which struggles past approximately 5× diameter before chip evacuation and heat become unmanageable—gun drilling is purpose-built for deep, straight, precision holes where standard methods fail.
How Gun Drilling Differs from Conventional Drilling
The fundamental difference lies in the tool design. A gun drill has a single cutting edge (not two like a twist drill), a hollow shank with an internal coolant channel, and a V-shaped groove running the length of the tool for chip evacuation.
| Feature | Gun Drilling | Conventional Twist Drilling |
|---|---|---|
| Cutting edges | Single (one-lip) | Two (double-lip) |
| Max depth ratio | Up to 300:1 | ~5:1 to 10:1 |
| Coolant delivery | Internal, through tool | External flood (usually) |
| Chip evacuation | External V-groove | Helical flutes |
| Self-piloting | Yes (guide pads) | No |
| Typical surface finish | Ra 0.4–0.8 µm | Ra 1.6–6.3 µm |
| Secondary ops needed | Rarely (eliminates reaming/honing) | Often required |
How Gun Drilling Works
The gun drilling process relies on three key components working together:
The Gun Drill Tool. A gun drill consists of a carbide cutting tip brazed or attached to a long steel shank with a V-shaped flute. High-pressure coolant is pumped through an internal hole in the shank, exiting at the cutting tip to cool the work zone and flush chips back through the V-groove.
Guide Pads for Self-Piloting. Immediately behind the cutting tip, carbide guide pads bear against the freshly cut bore wall. These pads provide continuous self-pilot action—they steer the drill on-axis throughout the entire cut depth. This is what allows gun drills to maintain straightness within 0.001" per foot (0.08 mm per 300 mm).
High-Pressure Coolant. Cutting fluid at 300 to 2,000+ PSI is delivered directly to the cutting edge. The coolant lubricates the cut, controls heat, and—most critically—provides the hydraulic force to push chips back along the V-flute and out of the hole.
The typical sequence: a pilot hole is drilled to guide entry, the gun drill is inserted, rotation and coolant flow begin, the tool feeds to full depth in one continuous pass, and rotation stops before retraction.
Key Capabilities
Gun drilling delivers impressive specifications that often eliminate the need for secondary finishing operations:
- Diameter range: 0.5 mm to 50 mm (0.020" to 2.0")
- Depth capability: Up to 10 meters (32 feet)
- Diameter tolerance: ±0.025 mm (±0.001") or better
- Straightness: 0.08 mm per 300 mm (0.001" per foot)
- Surface finish: Ra 0.4–0.8 µm (8–32 RMS) as-drilled
- Concentricity: Within 0.05 mm
Types of Gun Drills
Gun drills are manufactured in three main configurations:
Brazed tip. The most common type for diameters from 1.0 mm to 30 mm. A solid carbide tip is silver-brazed to a steel shank. The tip can be resharpened multiple times, offering good economy.
Solid carbide. One-piece carbide construction with no brazed joint. Offers maximum rigidity and the highest penetration rates. Best for small diameters (under 3 mm) where tool strength is critical.
Indexable insert. Replaceable carbide inserts and guide pads on a steel body. Used for larger diameters (16 mm to 65 mm). Eliminates regrinding—simply index the insert when worn.
Major manufacturers include Guhring (EB 100, EB 80, EB 800 series), Hartner (E 100, E 800 series), Star SU, Botek, and UNISIG. For a detailed breakdown of each type’s geometry, applications, and selection criteria, see our gun drill geometry and tool types guide.
Industrial Applications
Gun drilling is used across virtually every precision manufacturing industry:
Aerospace. Landing gear components, turbine shaft cooling holes, hydraulic system parts, and structural aircraft components. The aerospace industry requires the tightest tolerances and reliability that gun drilling provides.
Automotive. Fuel injector bodies, common rail systems, camshafts, transmission shafts, engine oil galleries, and connecting rods. High-volume automotive production relies on multi-spindle gun drilling machines for efficiency.
Medical. Cannulated bone screws (drilled 2.0 mm × 60 mm deep in titanium), intramedullary nails, surgical instruments, and dental implants. The process delivers the surface finish and precision required for implant-grade components.
Oil & Gas. Downhole tools, drill collars, valve bodies, and hydraulic components. Gun drilling handles the tough materials (stainless steels, Inconel) and extreme lengths required in this sector.
Mold & Die. Conformal cooling channels in injection molds and die casting tools, ejector pin holes. Gun drilling enables complex cooling channel geometries that improve cycle times and part quality.
Firearms. The original application—rifle and pistol barrels remain one of the most demanding gun drilling applications.
Advantages and Limitations
Advantages
- Single-pass efficiency. Deep holes are completed in one pass without pecking, reducing cycle time and tool wear.
- Excellent precision. Often eliminates secondary operations like reaming or honing, saving cost and handling time.
- Superior surface finish. The guide pads burnish the bore wall during cutting, producing a smooth finish.
- Material versatility. Works on almost all machinable materials—steel, stainless, aluminum, titanium, Inconel, brass, plastics, and ceramics.
- Tool life. Carbide tips can be reground multiple times, and indexable inserts eliminate regrinding entirely.
Limitations
- Requires specialized equipment. Dedicated gun drilling machines or high-pressure coolant systems add capital cost.
- Slower feed rates than BTA drilling for larger diameters (above 0.5"/12.7 mm).
- Not economical for shallow holes. Below 20× diameter, conventional drilling is faster and cheaper.
- Setup complexity. Requires skilled setup for pilot holes, guide bushings, and coolant system configuration.
- Tool cost. Gun drills are more expensive than standard twist drills and are application-specific.
Common Misconceptions
“Gun drilling is only for gun barrels.” While developed for firearms, gun drilling today is used across aerospace, automotive, medical, oil & gas, and mold making.
“Gun drilling requires a dedicated machine.” While dedicated machines offer the best performance, gun drilling can be performed on retrofitted CNC lathes and machining centers, especially for moderate depth ratios up to 40:1.
“Gun drilling is slow.” The process is slower per revolution than conventional drilling, but because it completes the hole in a single pass without pecking or secondary operations, total cycle time is often shorter.
When to Choose Gun Drilling
Gun drilling is the right choice when:
- Hole depth exceeds 20× diameter
- Straightness tolerance is critical (under 0.1 mm per 100 mm)
- Surface finish must meet Ra 1.6 µm or better
- Hole diameter is under 50 mm
- Secondary operations (reaming, honing) should be avoided
- The material is difficult to machine with conventional drills
Summary
Gun drilling is a proven, specialized process that solves one of manufacturing’s most difficult challenges: producing deep, straight, precision holes efficiently. Its single-lip tool design, self-piloting guide pads, and high-pressure coolant system work together to achieve depth ratios and accuracy that conventional drilling cannot match. While it requires investment in tooling and equipment, the ability to produce finished-quality deep bores in a single pass makes it indispensable in critical manufacturing applications.
For a deeper dive, see our step-by-step guide to how gun drilling works and our gun drilling parameters and speeds guide. For a complete overview, visit the gun drilling guide.