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AFTE Journal--Volume 44 Number 1--Winter 2012 19

Introduction

During a visit and tour of the SIG Sauer factory with Harald

Wagner in early January 2010, permission was given to

publish the manufacturing details and information pertaining

to SIG Sauer pistols to practitioners within the field of forensic

firearms examination.

The visit, article, and personal interest were initiated because

SIG Sauer uses two different manufacturing methods to rifle

their pistols depending on the client; these are electrochemical

rifling (ECR) and cold hammer forged rifling. As a result, the

manufacturing steps involved in making their barrels may

differ within one pistol model as well as from one model to

another.

This article will primarily focus on barrel manufacturing, but

will also discuss the pistol slide and frame manufacturing

processes as well as assembly, proofing and testing of the SIG

Sauer pistols before sale.

Barrel Manufacturing

In the literature, there are a number of articles that discuss

rifling methods [1-5] and specifically explain ECR [6, 7]

and cold hammer forging [8-10]. As a result, this paper only

summarises these methods and highlights aspects specifically

related to manufacturing at SIG Sauer.

Manufacturing of SIG Sauer 9 x 19 mm Pistols

By: Rachel S Bolton-King1

*, J Paul O Evans1

, Clifton L Smith2

, Jonathon D Painter3

, Derek F Allsop3

and Wayne M Cranton1

1. School of Science and Technology, Nottingham Trent University, Nottingham NG11 8NS, UK.

2. Electron Science Research Institute (ESRI), Edith Cowan University, Joondalup WA 6104, Western Australia, Australia.

3. Department of Applied Science, Security and Resilience, Cranfield Defence and Security, Cranfield University, Shrivenham,

Swindon, Wiltshire SN6 8LA, UK.

* Present address: Faculty of Sciences, Staffordshire University, Stoke-on-Trent, ST4 2DE, UK

Keywords: 9 x 19 mm, electrochemical, hammer forged, manufacturing, rifling, SIG Sauer

ABSTRACT

This article details the manufacturing processes and assembly of 9 x 19 mm calibre SIG Sauer duty, sporting and limited

edition pistols produced at the factory in Eckernförde, Germany.

The principal manufacturing focus for this paper is SIG Sauer barrel production, as two methods of rifling are utilized

in their pistols; electrochemical rifling and cold hammer forged rifling. However, pistol slide and frame manufacturing is

also discussed, as well as assembly, proofing and test firing of firearms before sale.

All rifle and pistol barrels manufactured at the Eckernförde

factory use the same raw steel material. These are long lengths

of cylindrical bar of varying diameter depending on the firearm

model the barrel is being made for. The raw steel is slightly

harder than normal steel, but not as hard as the finished barrel.

This approach is a compromise to reduce the wear of tools and

therefore the cost of manufacturing.

The raw material is then cut by a saw into smaller, more

manageable lengths, of equal size, no matter what firearm

barrel is to be made. These are then ready to be made into

barrels in the barrel production unit.

All SIG Sauer pistol barrels used to have hammer forged

rifling, however, the police and military wanted to reduce the

cost of pistols and one of the ways that SIG Sauer could do

this was to introduce a cheaper rifling. As a result, all duty

pistol barrels made after 2002 have been made with ECR

as the equipment and manufacturing process is significantly

cheaper. The rifling in sporting, limited edition and custom

pistols are still produced using the cold hammer forged

technique.

Duty Pistols (Post-2002) – ECR

This section describes the manufacturing process for

producing ECR barrels for SIG Sauer classic line duty pistols,

such as P226 and SP2022.

The shortened raw steel is fed directly into a CNC

milling machine, which can drill, mill and cut two barrels

simultaneously. There are two sets of cutting heads, but only

Date Received: June 28,2011

Peer Review Completed: October 5, 2011

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AFTE Journal--Volume 44 Number 1--Winter 2012

20 Bolton-King et al. -- Manufacturing of SIG Sauer 9 x 19 mm Pistols

one material feed point. During the milling process, the first

steel piece is cut off and turned away with cutting head 1, while

the second piece is produced at the same time with cutting

head 2. The third barrel is then made by cutting head 1 and so

on. The machine operates automatically and uses computer

aided manufacture (CAM). This process drills the internal

barrel bore and chamber, contours the outside of the barrel,

breech block with locking and camming surfaces (Figure 1) as

well as crowning the muzzle. The use of two cutting heads is

particularly noteworthy for any firearm examiner undertaking

toolmark comparison and investigation utilizing consecutive

barrel manufacture, or when investigating potential sub-class

characteristics. Another aspect to highlight is that there are

six CNC milling machines located at the factory that are all

used for barrel manufacturing, and a variable number may be

running at any one time to produce one batch of pistol barrels.

The number used depends on the size of the batch. At the end

of this stage there is no rifling inside the barrel bore.

The rifling is then imparted using an ECR machine, which

can rifle one barrel at a time and takes about 15 seconds. The

electrode (Figure 2) is held vertically at the base of the machine

and the barrel (anode) is held vertically above the electrode

(cathode). The barrel is then lowered on to the electrode while

a voltage is applied and the electrode rotates at the specified

rate, stripping the metal away forming the grooves. The

barrels milled from one (or more) CNC milling machine(s)

will have been grouped together and will not be separated into

barrels cut with each of the machines or individual cutting

heads. This means that consecutively produced barrels (at the

end of production) are highly unlikely to have been produced

sequentially from one tool/cutting head. However, SIG

Sauer does ensure that all machines producing the batch are

equipped with tools that are made from the same tool-batch.

This is to try to ensure that there are no differences in the

barrel tolerances.

After an internal polishing step, the barrel is hardened in two

areas (shown as discoloured areas on Figure 3) where forceful

contact will be made between the barrel and other pistol

components upon firing the weapon:

1. On the top, front section of the barrel breech block, which

hits the front of the slide’s ejection port during lock-up;

2. The barrel locking lug beneath the breech block, which

causes the barrel to move downwards after firing and the slide

remain open after the last round in the magazine has been

fired.

The hardness of these areas is tested in order to ensure that

they are within tolerance. If the hardness does not meet

the requirements, the inductive hardening process can be

repeated, numerous times if necessary, without affecting the

quality of the steel, and can be programmed to increase or

reduce hardness.

A robot then polishes the external surfaces of the barrel and

Figure 1: Annotated image of a 9 mm Luger SIG Sauer P250 barrel after CNC milling stage.

Figure 2: An electrode for rifling a 9 mm calibre pistol barrel.

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AFTE Journal--Volume 44 Number 1--Winter 2012

Bolton-King et al. -- Manufacturing of SIG Sauer 9 x 19 mm Pistols 21

moves the barrel into a laser machine, which engraves the

serial number onto the barrel. However, due to the use of two

cutting heads in each CNC machine for drilling and milling

the barrels, and the potential for multiple machines to be

used to manufacture one batch of barrels, a firearm examiner

cannot rely on the assumption that consecutive serial numbers

indicate consecutively manufactured barrels. This issue has

been highlighted previously and is summarised by Bonfanti

and De Kinder [11].

Barrels then undergo surface treatment. This is typically

bluing in an acid bath, however, another option is coating

with Physical Vapour Deposition (PVD – an alternative

to electroplating). This coating can be made of a variety of

different materials and protects the barrel from scratching and

rusting and increases the abrasion resistance and corrosion

resistance (compared to the untreated steel), therefore

increasing the lifespan of the barrel. The guarantee of SIG

Sauer ECR barrels is 15,000 rounds, however, a definitive

lifespan has not been determined.

Pistols (Pre-2002) and Sporting Pistols – Cold Hammer

Forged Rifling

Sporting pistols are required to be both accurate and precise,

of very high quality and have a long lifespan; therefore,

these pistol barrels are still cold hammer forged. Custom

pistol barrels, and pistols with silencers that require an

extended barrel with a threaded end, are also manufactured

and rifled using the hammer forged process. The SIG Sauer

manufacturing steps for such pistol barrels are summarised

as follows:

1. central hole drilled through shortened length of cylindrical

raw steel material (same specification of steel as used for ECR

barrels);

2. outer steel surface milled in CNC machine;

3. drilled hole polished using honing machine;

4. cold hammer forging of drilled and milled bar material;

5. hammer forged bar cut into 5 pieces to make 5 pistol barrels;

6. muzzle crowned, outer surface of barrel and inside chamber

contoured with CNC milling machine;

7. metal disk attached under un-milled barrel chamber using

frictional welding;

8. outer surface of breech block with locking and cam surfaces

contoured by CNC milling;

9. robotic polishing of external surfaces of the barrel;

10. laser engraving of serial number onto the barrel;

11. surface treatment, typically bluing or PVD coating;

however, the customer can request no such treatment.

The cut raw steel bar is placed in a lathe and a gun drill is

used to produce a central hole. The diameter of the drilled

hole is dependent on the intended barrel calibre, but is slightly

larger than the required diameter of the finished barrel. This

is because the hammering process will reduce the size of the

barrel bore to the correct diameter.

The outside of the drilled steel bar is then milled in one of

ten multifunctional CNC milling machines prior to hammer

forging. This process also removes any surface rust present on

the outside of the material.

The bore of the steel bar is then very finely polished several

times on a honing machine to remove most of the drilling tool

marks. This process also ensures that the hole is a constant

diameter and is uniform along the length of the steel.

The honed steel bar is then taken to be cold hammer forged in

a separate production unit. The hammering machine contains

4 hammers. Opposite the hammers is a chuck which clamps to

the end of the steel bar material and holds the mandrel (Figure

Figure 3: A pistol barrel illustrating the discoloured areas of inductive hardening.