Gun Drilling & BTA Drilling: Definitive Gun Drill Guide (2023)

Gun Drilling & BTA Drilling: These are the right tools for the absolute deepest of Deep Hole Drilling. “Deep Hole” is defined by drill diameters, and specifically the depth to diameter ratio. When used properly, gun drilling can produce straight holes that are much deeper than conventional style drills are capable of.

Here’s some quick information on various deep hole drilling solutions from our Deep Hole Drilling Guide:

Gun Drilling & BTA Drilling: Definitive Gun Drill Guide (1)

The depth to diameter ratio chooses the right process to produce straight deep holes…

While we can use special g-code such as the Conversational Programming of G-Wizard Editor to extend the reach on deep holes beyond Parabolic Flute Drills and Peck Drilling, to go really deep takes even more specialized tooling. Premium solid carbide twist drills are all done by 20 diameters, to maybe a bit more with hand tuned custom cycles.

Typically, Gun and BTA Drilling are done on special deep hole drilling machines that are designed for the purpose. Such machines are capable of contra-rotating both the cutting tool (Gun or BTA Drill) and the workpiece, which gives the best results on large depth to diameter ratio holes.

Gun drilling can also be done on a lathe, but the disadvantage is that the lathe can only rotate the workpiece and not the drill at the same time.

Straight deep holes are not easy!

What is Gun Drilling?

Gundrilling developed to help make straighter more accurate gun barrels. As you can imagine, deep straight holes are critical to accurate gun barrels.

Gun Drilling & BTA Drilling: Definitive Gun Drill Guide (2)

(Video) Gun Drilling Machine - Swaraj Automation

It uses a fairly simple geometry solid carbide tip on a long, thin cutting tool that pumps fluid through the core of the tool to flush chips from the tip back out through generous straight flutes:

Gun Drilling & BTA Drilling: Definitive Gun Drill Guide (3)

Gun Drills by Sterling

The tips are similar in geometry to solid carbide twist drills except there is no twist–the flutes are straight. Coolant under pressure forces the chips back out along the length of the grooved shaft. These tips are either solid carbide or brazed carbide–it takes a tough cutting tool to deal with these depth to diameter ratios.

Gundrilling equipment for deep hole drilling consists of

  • A thin cutting tool with solid carbide cutting edge(s), the gun drill itself.
  • Toolholding components to pump the coolant and evacuate chips.
  • A machine–either a lathe or a dedicated gundrilling machine.

Why does gundrilling work better for straight deep holes? It’s all about the chips. In a deep hole, it gets harder and harder to remove the chips as depth to diameter ratio increases. The deeper the hole the more difficult chip removal becomes. Pumped coolant at a pressure that guarantees chips are blown back out of the hole together with an avenue the chips can move through are key.

Add a solid carbide tip and you’ve got a gundrill for virtually any material.

When to Consider Gun Drilling

Among deep hole drilling solutions, choose gun drilling when:

  • Hole depths are greater than 20x.
  • Deep Holes would require reaming or honing to meet tolerances. Gun drilling requires no reaming or honing because the surface finish of the drilled hole is already very good.
  • With drilled diameters of less than 20mm. Larger diameter deep holes can be done more efficiently with BTA Drililng.

Deep hole drilling can be done on virtually any material when these conditions are met.

Sometimes even relatively shallow holes (by gun drilling standards) benefit from gun drilling when straightness, diameter, and surface finish requirements are high. The hole size, finish, and straightness of a gun drilled hole are all higher than with twist drilling and other deep hole drilling solutions, so eliminating a second reaming or honing op via gun drilling may save time.

(Video) BTA Deep Hole Drilling Machine

Solid carbide twist drills are not always the answer.

Gun Drilling on a Lathe

While gun drilling can be done on a lathe, it is better done on a special-purpose deep hole drilling machine. The advantages of the deep hole drilling machine include the ability to rotate both workpiece and gun drill (in opposite directions), whip guides to support the long drill and workpice, plus high pressure coolant for better chip evacuation.

Contra-rotating tool and workpiece contributes to straighter drilled holes. Dedicated deep hole drilling machines also have more sophisticating monitoring of loads and coolant pressures that correctly identify when the tool is dulling and needs to be changed.

Anthony Fettig, CEO of UNISIG, says the dividing line is at about a 40:1 depth to diameter ratio. That’s the point where purpose-built deep hole drilling machines start to have a significant performance advantage over using gun drills on conventional lathes and milling centers.

Even so, gun drilling on an ordinary lathe can still be effective. Here’s a gun drill in operation on a manual engine lathe with just a mist coolant unit:

Gun Drilling & BTA Drilling: Definitive Gun Drill Guide (4)

Image via CTE Magazine.

Such a simple rig will take holes to much greater depths than ordinary twist drills can reach.

Given that whipping can create a real safety hazard as well as completely destroying the gun drill, some important procedures must be followed when gun drilling on lathes without whipping guards:

  1. Create a pilot hole at least 1 to 2 diameters deep and 0.0005 – 0.001″ larger than the gun drill.
  2. Position the gun drill in the hole before starting rotation.
  3. Always stop rotation before removing the gun drill from the hole.
  4. Consider a steady rest on the lathe to help stabilize gun drills. If you don’t have a steady rest, you may have to use a series of progressively longer gun drills. Try to keep less than 40 diameters length of gun drill unsupported.
  5. When using mist instead of high pressure coolant, reduce feedrates by 60%. The smaller the hole, the more important higher pressure coolant becomes.

Gun Drills are happier with cutting oil than typical water soluble coolant used with CNC. Keep the coolant temps below 80 degrees F so you don’t lose viscosity on the oil. All that is telling you is that where coolant is concerned, lubrication and keeping chips evacuated is more important than cooling.

(Video) botek BTA Drilling System

Check with application support for specific coolant recommendations based on the depths of your hole and the tool in use.

Coolant guidelines for gun drilling:

DiameterIdeal PSIMin PSIGPM @ Ideal PSI

Another area to fine tune for your particular application is the nose grind or geometry. If not specified, most gun drills have a N-8 nose grind and R1 relief. This is fine for steel or inconel. But, in the case of aluminum or brass, you’re better off with an N-4 nose grind and R4 relief. Consult your gun drill manufacturer for best results as they’re the experts.

Gun Drilling Feeds and Speeds

Our G-Wizard Feeds and Speeds Calculator will figure Gun Drill feeds and speeds for various depths:

Gun Drilling & BTA Drilling: Definitive Gun Drill Guide (5)

In fact, G-Wizard can produce feeds and speeds for nearly all deep hole drilling solutions needed to manufacture your parts.

You can download and be using G-Wizard today!

Gundrill Types

Choosing the right tooling will maximize your performance.

Single Flute Gundrill

A single flute gundrill is the most common design. A single flute with straight, not-helical flutes will produce shorter chips which are easier to evacuate than long ones.

Double Crimp Gundrills

The term Double Crimp essentially means cutting with 2 flutes. Double crimp gundrills have 2 chip evacuation flutes, but they’re smaller than a single flute gundrill, so they must be used on a metal that produces smaller chips like cast iron and aluminum. Because double crimp gun drills have 2 flutes, they can operate a higher feedrates than single flute gundrills.

(Video) Setting up of a TBT Deep hole drilling machine with TBT gun drills

If you’re in doubt about whether a double crimp will work in your application, share your specific requirements with applicaton support at your vendor.

Related Tooling

High Precision Rifle Buttons

High precision rifle buttons (or rifling buttons) are precision carbide tools for cutting the rifling grooves on a gun barrel. A rifle button can be pushed or pulled through the barrel, but this is done without rotation (so more like a broaching operation).

Push and Pull Reamers

A push or pull reamer may be used to remove 0.003″ to 0.004″ of material before using a rifle button. This ensures accurate ID and good surface finish of the barrel.

Gundrill Wear

It is important to remember that the most critical interface where the carbide tip is subject to the most traumas is the entry and exit of the part whenever the boring cycle is interrupted. Tool life should improve if you minimize interruption of the boring cycle to avoid that critical interface.

What is BTA Drilling?

There are several differences that separate BTA Drilling from Gun Drilling:

  • BTA Drilling involves a drill bit mounted on a long tube as tool.
  • Chips are evacuated through the center of the tube and coolant flows around the outside of the tube, which is a smaller diameter than the hole.
  • BTA cutters are either brazed or inserted carbide, not solid carbide.

BTA stands for Boring and Trepanning Association. BTA Drilling can achieve feedrates that are 5-7 times that of Gun Drilling, hence it can deliver a lot faster boring cycle. The downside is the tooling is bulkier, so it can only be used on larger diameter holes.

Here’s a simple animated diagram showing how BTA Drilling works:

In-House Deep Hole Drilling Solutions?

Many shops outsource deep hole drilling solutions for metal, particularly when there is a need for BTA Drilling or the kind of very deep holes where dedicated deep hole drilling machinery really shines. However, if your manufacturing needs can be handled with a gun drill on a lathe competitively, it’s not that hard to bring the process in-house.

Doing so can enhance your shop’s manufacturing profits or at least reduce manufacture turnaround times.

(Video) DeepTri-Drill - Remarkable productivity and stability in deep hole drilling!

Before purchasing any gundrill or BTA tooling, phone your vendor’s application support to be sure you are getting the best cutting tool for your manufacturing application. Give their experts your specific requirements. Straight deep holes need all the expertise you can get to ensure a quality end result when boring stock. When it’s as easy to come by as a phone call to application support to discuss your specific requirements, why miss out?


We given you some quick information about how to succeed with these deep hole drilling solutions and an idea of what tooling is available. You should understand the basic information needed after going through this content.

A little work with your vendors on specific requirements and you’ll no longer be challenged by hole depth. Having experience in this area will be helpful to most any shop making the types of parts or products that require deep holes.


What is the difference between gun drilling and BTA drilling? ›

BTA Drilling vs Gun Drilling

BTA drilling machines introduce coolant around the tool head, and evacuate chips through the drill and machine spindle, compared to gundrilling, where coolant is introduced internally and chips exit through an external groove.

What is the BTA drilling process? ›

The BTA (Boring Trepanning Association) process involves the use of a specialized drilling tool with a long inner tube that allows the extraction of the cutting fluid and the metal chips more efficiently. These tools have a minimum diameter of 15.6 mm but can reach up to 300 mm in diameter.

What should the coolant pressure be on a gun drill? ›

5) Coolant PSI, Type, and Filtration

Typical recommendations are anywhere from 1,500 PSI for holes below 0.15" diameter to 500 PSI.

What is the difference between a gun drill and a drill? ›

A gundrill tool differs from a conventional twist drill by its unique head geometry; a standard gundrill has a single effective cutting edge that removes chips as it advances into a metal workpiece.

What are the three types of drilling methods? ›

Here are the five common types of oil drilling techniques.
  • Cable Drilling.
  • Directional Drilling.
  • Electro-Drilling.
  • Rotary Drilling.
  • Dual-Wall Reverse-Circulation Drilling.
Feb 25, 2022

What are the four main types of drilling? ›

What drilling technology should you choose?
Drilling typeSoil type
Rotary drillingSoft rock
Down-the-hole drillingHard and cracked rock (limestone, granite, etc.)
Top hammer drillingConsolidated land
Auger drillingClay, clayey sand, gravel
3 more rows

What are the 4 steps in the drilling process? ›

A typical drilling process has the following stages:
  • Preparation. Preparing a drilling site involves ensuring that it can be properly accessed and that the area where the rig and other equipment will be placed has been properly graded. ...
  • Drilling. Vertical Drilling. ...
  • Well Completion. ...
  • Production. ...
  • Well Abandonment.

What are the three major operations of core drilling process? ›

Three major operations make up the core drilling cycle: the actual drilling into the ground (or the advancement of the bit), retrieving the core sample from the core barrel using one of the 2 methods listed above, and replacing the equipment with a clean, lubricated inner tube assembly which will allow you to resume ...

How much PSI is in a coolant line? ›

What about coolant hose? The cooling systems in most late model cars and trucks are designed to operate at 13 to 18 PSI or less. So most radiator and heater hoses never see the high side of 18 PSI, even if the engine runs hot and overheats.

Why the coolant is necessary while drilling? ›

Friction, in turn, can result in ragged edges or other issues in the material you are drilling. In some cases, it can also lead to damaged drill bits or even damaged tools. To prevent problems from happening, you will need to use coolants and lubricants during drilling.

What does a 15 psi radiator cap do to the boiling point of antifreeze? ›

A cooling system using a 15 psi radiator cap will add 45 degrees to the boiling point for a final boiling point of 268 degrees. The real purpose of pressurizing your cooling system is to give the vehicle a higher operating zone in case of extreme conditions.

What is the strongest type of drill? ›

Carbide is the strongest drill bit for metal and is typically reserved for professional-grade tools. Black Oxide is a coating added to HSS drill bits that helps reduce friction and speed up drilling through hard metals.

Why it is called a gun drill? ›

They are used for deep hole drilling—a depth-to-diameter ratio of 300:1 or more is possible. Gun barrels are the obvious example; hence the name.

Why use a drill press over a hand drill? ›

The main difference is the amount of structure -- with a hand drill, it's difficult to be sure that the holes you're drilling are exactly perpendicular to the piece, but this isn't a problem with the drill press. The drill press isn't a very large machine, but it has quite a bit of flexibility built into it.

What are the two main types of drills? ›

The two major types of the drill are manual and electric drills. The common features they have today include multi-function power, selection of driver bits, and varied drilling power.

What are the two most common type of drilling method? ›

On the basis of material obtained from the hole, there are two main types. 1. CORE DRILLING: where by means of drilling core can be obtained 2. NON CORE DRILLING: where only rock cuttings along with slurry can be obtained.

What are the two 2 main types of drilling bits? ›

Currently in the drilling industry, there are two main categories of drilling bits: rolling cutter bits and fixed cutter bits.

What is the order of drilling? ›

The sequence of drilling operations involves drilling large diameter holes first and running large diameter conductors then drilling progressively smaller hole sizes, installing smaller and stronger casings and liners as downhole pressures increase.

What is the most common form of drilling used today? ›

How wells are drilled[edit] The most common method of drilling wells uses rotary drilling (Figure 1). A drilling bit is attached to the end of a long string of jointed, hollow drill pipe, and the whole assembly is rotated by a motorized turntable at the surface, the rotary table.

What is the most widely used form of drilling? ›

Depending on the purpose and budget of the project, there are several types of drilling methods available, but reverse circulation and diamond are by far the most common for mineral exploration.

What are the basic drilling operations? ›

Drilling operation is the first contact between the formation and the nonnative fluids and equipment. Drilling fluids play a vital role during the drilling operations by lubricating the bottom-hole assembly, cooling the drilling bit, lifting-up the cuttings, and forming impermeable filter cakes.

What is a drilling rig called? ›

In the petroleum industry, a derrick consisting of a framework or tower of wood or steel is erected over the deep drill holes of oil wells to support the tackle for boring, to raise and lower the drilling tools in the well, and to insert and remove the well casing… In petroleum production: The derrick.

What is rig 6 drilling unit? ›

Rig 6. Our Rig 6 is a conventional box on box substructure with a “double” derrick that is hydraulically raised and cable scoped with a depth rating of 10,500 feet with 4 ½” drillpipe.

What are the 3 types of oil rigs? ›

There are three primary rig types. Jackups, semisubmersibles and drillships make up the majority of the offshore rig fleet and all are used worldwide.

What does core mean in drilling? ›

A modern core drill is a drill specifically designed to remove a cylinder of material, much like a hole saw. The material left inside the drill bit is referred to as the core.

What are all three cutting parameters of drilling operation? ›

In this research work, the optimal cutting parameters speed, feed rate and lip angle of the drill bit for drilling operation is identified to minimize the tool wear and to improve the accuracy of the work.

What happens if I use a higher psi radiator cap? ›

Because cooling systems are designed for specific pressure. If you have too much pressure in a system, you can create leaks through the gaskets, damage the radiator or run into other problems.

Can you put too much coolant in your radiator? ›

Most of the time, excess coolant is expelled from an overflow hose. You'll likely see a puddle of coolant beneath your car if this has happened. In worst case scenarios, overfilling your antifreeze tank can lead to electrical damage if overflow comes into contact with engine wiring.

Why is it not good to add cold water to a hot engine? ›

Do not pour cold water into a still-hot radiator — it could cause the engine block to crack due to the sudden change in temperature. If you absolutely have to add water while the engine is still warm, pour slowly while the engine is running in neutral or park.

Why do people use water instead of coolant? ›

There are many people who believe using distilled water instead of coolant is suitable for vehicles driven in hot climates. This usually comes down to their mistakenly believing that antifreeze is only necessary for vehicles that will be driven in cold-weather conditions.

Why is water a better coolant than oil? ›

The specific heat of water or water/glycol is about twice that of oil, so a given volume of water may absorb more engine heat than can the same volume of oil. Therefore, water may be a better coolant if an engine is permanently producing large amounts of heat, making it better for high-performance or racing engines.

What is the best pressure for a radiator cap? ›

Most radiator pressure caps keep the system pressure at 16 PSI so the engine coolant can get considerably hotter without the fear that it will boil off. If there is no pressure in the cooling system, the coolant will boil off.

Can a radiator cap hold too much pressure? ›

High-Pressure Radiator Cap

Unchecked high pressure could cause damage to the radiator, heater core, hoses or water pump seal. The pressure cap also prevents radiator hoses and tanks from collapsing. As the engine cools it causes a vacuum in the cooling system.

How many degrees will a 13 psi pound radiator cap raise the boiling point? ›

Water boils at 212° F, increasing the pressure in a closed system increases the boiling point. This means that a cap rated at 13 lbs. will increase the boiling point in a system by 39° F.

What is the hardest metal to drill through? ›

Carbide. Carbide is the hardest material used in drill bits.

What is stronger carbide or cobalt? ›

Cobalt Drill Bits Pros. As we have seen, both drill bits are made from high-grade materials and perform well. But in terms of strength, solid carbide drill bits are superior, with a hardness of 75 HRC and cobalt's hardness of 65 HRC on a Rockwell scale.

What's the hardest metal to drill? ›

Carbide: The hardest and most brittle of the drill bit materials, it's used mostly for production drilling where a high-quality tool holder and equipment is used. It should not be used in hand drills or even drill presses. These bits are designed to drill into the hardest materials.

How accurate is gun drilling? ›

Gundrilling is capable of maintaining accuracy to extreme ratios of up to 400:1. The process can be performed in 3 manners: Rotating tool, stationary workpiece.

What is drill called in the military? ›

Modern drill is essentially of two types: close-order and extended-order, or combat drill. Close-order drill comprises the formal movements and formations used in marching, parades, and ceremonies. Combat drill trains a small unit in the looser, extended formations and movements of battle.

What is the tolerance of gun drilling? ›

Depending on the material and application, gundrilling is always more precise, and often faster than conventional drilling. Tolerances as close as 0.0003" have been consistently held and surface finishes of 16 to 20 micro-inches are expected in gundrilling.

What are 3 rules for drill press? ›

Safety Rules

Don't wear loose clothing or gloves, keep long hair tied back. These items will get caught in bit or spindle. Never adjust the drill press or setup while it is running. Never leave chuck key in press.

What are 5 important rules for a drill press? ›

Drill Press Safety Rules
  • Run drill at correct RPM for diameter of drill bit and material. ...
  • Always hold work in a vise or clamp to the drill table.
  • Use a correctly ground drill bit for the material being drilled. ...
  • Use the proper cutting fluid for the material being drilled. ...
  • Remove chips with a brush, never by hand.

What are the two main types of drilling? ›

The main types of drilling systems include rotary drilling, percussion drilling, and rotary-percussion drilling. Rotary drilling involves a rotating drill bit, percussion drilling uses a hammering action, and rotary-percussion drilling combines both methods to penetrate various soil and rock conditions.

What are the two most common types of drilling methods? ›

On the basis of material obtained from the hole, there are two main types. 1. CORE DRILLING: where by means of drilling core can be obtained 2. NON CORE DRILLING: where only rock cuttings along with slurry can be obtained.

What are the two types of core drilling? ›

There are two main types of core drilling: hard coring and soft coring. This refers to the type of lithology each method is suited for.

Are there two types of drill? ›

All the drills are classified as corded or cordless drills. The cordless drills are used for light and easy tasks like some DIY projects. They are also an ideal choice for performing tasks in areas that are tough to reach. On the other hand, corded drills are used for heavy-duty machining.

What is the most common type of drilling? ›

The first type of drill bit is the twist bit. As its name suggests, this type of bit has a twisting action that helps it to bore through material. Twist bits are the most common drill bit used, and are available in a range of sizes and are ideal for drilling holes in wood and metal.

Which method is fastest for drilling? ›

Rotary percussion drilling is the fastest and most economical method for drilling grout holes in rocks. On the other hand, rotary drilling is frequently used in soils.

What is the most common type of drill used today 2 points? ›

Twist drills are the most widely used of all drill bit types.

What is drilling for oil called? ›

Hydraulic fracturing or “fracking” is one form of stimulation used to facilitate the production of underground resources such as oil and natural gas wells, geothermal energy, and water. Another form of well stimulation is called acidizing and will be discussed later.

What is the deepest drill core? ›

This is the Kola Superdeep Borehole, the deepest manmade hole on Earth and deepest artificial point on Earth. The 40,230ft-deep (12.2km) construction is so deep that locals swear you can hear the screams of souls tortured in hell.

Can you use a normal drill for core drilling? ›

Yes, you should be able to use it for that, take it easy, give the drill a rest every few minutes. Have hammer off, drill the pilot first, clean out rugularly.

What is the difference between core and RC drilling? ›

The kind of sample each drilling method allows differs. Diamond core drilling is good for precise sampling and analysis of layers; RC drilling is good at extracting bulk samples. Drilling rate can depend on the ground conditions but RC drilling tends to be quite a lot quicker than diamond core drilling.


1. MTDCNC talks Gun-drilling with the experts at Guhring
2. Deep Hole Drilling Techniques
(Tools and Tech)
3. The Ultimate Guide to BTA Drill Bit by (DIC TOOLS) | Drill Bit | Dedicated Impex Co.
4. Deep Hole Drilling | CMZ, Turning YOUR world
5. Tri-Fine - Indexable deep hole drills featuring inserts with chip splitter and built-in wiper
6. Hammond & Co. Spraymist/Ventec Instructional Video
(Hammond & Co)


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