Fliegers-Selbstlader-Karabiner FSK15

(Flyers Self-Loading Carbine)

After Mexico refused to pay for the remainder of the approximately 4,000 Mondragon rifles, SIG was stuck with a rifle that no one wanted. Lucky for SIG, the Great War (that would be WW1) was about to get started. Germany purchased the entire stock from SIG. Did Germany really need such a small amount of Mondragon rifles, or was it to deny their use to the French and British forces… who knows?

This weapon’s machined tolerances were much too critical for the muck and abuse of the trenches, these guns were designed for much cleaner environments like the dry desert of Mexico. Not able to find a desert in France or Belgium the German army decided the navy or the flying Corp (reconnaissance airplanes and observation balloons) would fit the bill perfectly.  In 1915 the Model 1908 was modified for aircrews and redesignated the FSK15.

However, once the Maxim machine gun became plentiful the FSK15’s were eventually phased out, after all a belt fed Maxim machine gun gave superior firepower to both pilot and gunners.  Rather than invest in R&D for so few a number of guns the rest were eventually relegated to emergency use only.

Modifications

The big changes from the Model 1908 are as follows; shortening the barrel by 20mm, shortening the buttstock about by 20mm, adding a 30-round drum magazine, modifying the rifle so it only operates as an autoloading weapon.

The autoloading only function, was accomplished with a single screw in the gas regulating valve.   An observer in flight accidentally going into manual mode was the probable motivation for this modification.

The following visual modifications were made to the Model 1908 to the FSK 15. Most all Mondragon’s Model of 1908 were converted to the Model 1915/FSK15.

1. Markings, or lack of.

 The Mexican crest over the chambers were never applied on the FSK15.

2. Shortening the barrel and buttstock by 20 mm or 3/4 inches.

Top: Model 1908
Bottom: Model 1915 without drum magazine

3. Addition of a 30 round drum Magazine

The standard magazine well was adapted to take a 30-round drum magazine.

(The floor plate, spring and follower were removed, a new magazine catch was added)

The thirty (30) round drum magazine was for aircrew use.  Five (5) magazines came with each gun. Each drum would be marked with a small metal tab indicating which magazine it is. i.e., “4-1234” (the 4th drum to the serial number of the gun)

A lever on the rear of the drum wound a spring that forced the ammunition up into the chamber area. Just like the Thompson submachine gun except the Thompson was in the .45 Auto pistol round.

The magazine well has the “L” shaped magazine catch for the drum. A claw at one end and push button at the other end

4. Prevention of the charging handle from disconnecting from the return spring

A positive locking device of the manual charging option was incorporated on all FSK 15’s. The knurled rectangle has a push button underneath to de-activate this feature.

In the photo below, the gun on the left has the charging handle locked.  To reload, you simply pull back hard against the return spring, just like charging an autoloader today. As the shooter pulls back the charging handle, you manually extract the spent round. Upon releasing the handle, the bolt slams forward loading a new round. Firing is semi-automatic from that point on.  I’m still not sure why the device is needed.

The middle gun in this photo has overridden the lockout and is able to cycle the action without interference of the return spring. The soldier would be required to slam home the bolt.

The gun on the right in this photo is the original design. Pulling the charging handle on the outside fat portion releases the hook that engages the operating rod. This allows the shooter to manually load a new round, eliminating the need to overpower the massive return spring. All modern semiautomatic rifles do not have this feature. (At least all the ones I know of.)

There was a misconception that this feature was added because the gun jammed so much that it needed a manual option. If it jammed that much, it would have not been approved for service.  All SLR’s will jam if not cleaned properly, if you carried an M-16 in the 60’s, you would be familiar with the jamming problem.

5. Stock Numbering

A number was stamped into the wood on the left side, slightly above and forward of the magazine. All the numbers start with 81 and have a decimal place with one or two numbers following, i.e. 81.4, 81.5, 81.55, 81.6 etc.

(The purpose of this number still eludes me.)

It was suggested that they are unit numbers. There is no known documentation that I can find indicating which German units the Model FSK15 were issued to.

6. Gas System

The gas selector/regulator was normally allowed to rotate. Not sure why this bothered the Germans so much that they put a in a screw to prevent rotation.

After shooting a few rounds, I’m thinking that the locking screw would prevent the rifle from accidentally being released from the semi-auto mode into manual mode. This could be catastrophic when you are a couple of thousand feet in the air shooting it out with a fighter and you revert to only having a bolt action rifle.

7. Receiver End cap, Retaining Screw

The END CAP was modified with a retaining screw to prevent a worn cap from falling off.  An original model 1908 is on the left and the modified FSK15 on the right.

8. Foward Sling Swivel band reinforcing

Specification Sheet for the Model 1915 or FSK15

Country of Design: Mexico

Designer: Manuel Mondragon

Used by: Germany during WW1

Description

• Caliber: 7x57mm Mauser
• Type of reloading mechanism: Semi-automatic, gas operated.
• Drum magazine capacity: 30 rounds

Production

• Quantity: 3,500 – Germany converted all the purchased 1908’s to the Model 1915. They were supposedly destroyed after the war, and yet at least 50 + have been accounted for.        
• (I keep an ongoing list of serial numbers of as many as I can. Let me know if you have one).
• Bannerman’s was selling them as war surplus from 1925 until 1966 according to the Bannerman’s sales catalogs.
• Years made: Converted around 1915
• Manufacturer:  Swiss Industrial Company (SIG), Neuhausen, Switzerland
• Entered service: Probably around 1915

Specs

• Weight: 9lbs 3oz
• Barrel length: 25 inches
• Total length: 45.5 inches
• Sights: 400-2000
• Serial number range: between 200-4000

Known examples…………………………………………..42