7.5x55 Swiss (GP11)

History

 
Following European trends of the mid to late 1880’s and after exhaustive testing, the Swiss army adopted a 7.5mm small bore cartridge designed by Eduard Rubin and a straight pull repeating rifle designed by Rudolph Schmidt. The Schmidt-Rubin rifle was officially adopted in 1889, replacing the 10.4mm Vetterli rifle, the new 7.5x53.5mm cartridge was officially adopted the following year bearing the designation GP90.
 
The GP90 was initially loaded with a 211gr paper patch bullet loaded to 1970fps. The nominal bore diameter for the 1889 Schmidt-Rubiin was .304". The land diameter was 7.51mm or .296". The paper patched bullet diameter was approximately .321" (through to .323") at its widest. Underneath the paper, the bullet diameter was .316". Although a patch was employed to reduce fouling, the primer employed produced considerable bore corrosion. The cartridge was therefore modified to use a less corrosive primer with a change in designation to GP90-03.

Further modifications lead to the GP90-23. This featured a 1mm longer 54.5mm case, a change in bore diameter from .304” to .3075” along with the adoption of a 190gr Cupro nickel jacketed round nosed bore riding bullet loaded to 2050fps.  After cartridge modifications, Swiss military officials discovered weaknesses in the M1889 rifle action. By 1895 a redesign of the action shifted the bolt locking lugs from the rear to the front of the action, resulting in the stronger M1889-96 rifle adopted in 1896.
 
In 1905 Germany adopted a superior, lighter faster pointed bullet for their military service rifle forcing other European countries to make similar advances. By 1908 the Swiss army had developed a lighter and handier rifle and eventually a new cartridge, the GP11 or 7.5x55 (1911). The GP11 load consisted of a 174gr .3087” bullet giving 2640fps. Initially production of the new rifle occurred by re-barreling M1889-96 rifles to fire the GP11 cartridge. In 1913 production of a new, rather than re-worked rifle, began with the introduction of the M1911 rifle. The M1911 rifle remained in service until the adoption of the K31 rifle in 1931. The Karabiner (carbine) 31 is considered the finest of the Schimdt-Rubin style rifles delivering smooth reliable feeding and superb accuracy.
 
The K31 was eventually superseded by the selective fire Stgw 57 chambered for the GP11, the GP11 cartridge and Stgw57 remaining in service until 1983. Both rifle and cartridge were finally replaced by the SIG SG541 rifle firing Switzerland’s current service cartridge the GP90, essentially the 5.56 NATO (.223 Rem).
 
Prior to its retirement from service in the 1980’s most Western countries had little experience with the Schimdt-Rubin style rifle or GP11 cartridge. Despite this fact, for decades in almost every major Western community, Swiss expats have taken great pride in shooting the K-31 rifle at Swiss club target ranges.  Today Swiss military rifles and ammunition are more freely available, appealing to hunters and collectors alike. 
 

Performance

The GP11 is a unique and well designed cartridge. Outwardly the cartridge case appears smaller than the .30-06 Springfield and similar to the 6.5x55 and the 7x57.  Closer inspection reveals that the rim and head diameter at 12.6mm (.496”) and 12.5mm (.493”) respectively are larger than the .30-06 at 12.01mm (.473”) and 11.49mm (.470”).  Although the .30-06 is longer at 63mm (2.5”) the 55mm (2.185”) GP11 Swiss military cartridge case has identical powder capacity to commercial Winchester .30-06 brass. In fact if the GP11 case were the same length as the .30-06 it would hold approximately 10 grains more powder. 
 
Unlike the .30-06 cartridge and Springfield rifle, Swiss military rifles were designed for lower chamber operating pressures of 45,500psi. The original GP11 load remained unchanged until its retirement and featured a 174gr .3087” bullet giving 2640fps in the 25.65” barreled K31 and only a little more velocity in the longer 30.7” barreled M1889-96. Although operating at mild pressures, the 7.5 Swiss is a powerful cartridge, achieving the same killing performance as produced by the .30-06 and long barreled .308 rifles. With so many projectile designs to suit a wide variety of hunting situations, loads for the 7.5 can be tailored to suit a wide range of hunting situations.
 
The Schimdt-Rubin and K-31 rifles are smooth, reliable and accurate. Unfortunately these rifle actions do not offer top metal in the right areas to allow the mounting of standard bases and rings for normal scope use. Instead, scout style mounts are made to fit the rear sight ramp housings. Off center side mounted scope rails are also available as aftermarket items. The Swiss actions can be fitted with custom made bridge style mounts extending from the very rear of the action over the breach but making such a mount is labor intensive .

   

Factory Ammunition

Of the former GP90 and GP90-03, there are small scale U.S manufacturers who produce rare ammunition and occasionally produce GP-90 ammunition using shortened 7.5x55 brass loaded with unpatched .308 caliber bullets.  

As for the GP11, like most military surplus ammunition, full metal jacket GP11 ammunition does not lend itself well to hunting but can be improved by hollow pointing which produces a fast expanding bullet suitable for medium game but cannot be relied on to give deep penetration. Another common practice is to remove the FMJ projectile using a kinetic bullet puller and replace it with a 165 through 180gr soft point projectile.

Commercially loaded GP11 sporting ammunition is now somewhat rare. Norma produce a load featuring their 180gr core bonded Oryx bullet at 2493fps for a realistic 2400fps. The Oryx bullet is particularly suited to medium game in the 90 to 180kg range giving relatively deep penetration but on lighter game where not enough resistance is met, kills can be slow.

PPU currently produce a 174 grain load at an advertised muzzle velocity of 2525fps. The PPU jacket is similar in thickness to the Sierra 180 grain Gameking and Prohunter bullets (rather stout) but with a wide jacket mouth and plenty of exposed lead to help initiate expansion. This is an adequate general purpose load for hunting medium game out to moderate distances. 
 

Hand Loading

Regarding the GP90 and GP90-03, these can be loaded using Norma or PPU 7.5x55 brass trimmed to their respective 53.5 or 54.5mm case lengths and run through 7.5x55 dies. The safest method for loading the GP90 cartridge in an aged rifle, is to use a paper patched cast bullet loaded to mild speeds. That said, bullet casting and paper patching is quite an in depth subject in comparison to general reloading. As an alternative, as per the loads mentioned in the factory ammunition section, it is possible to use a jacketed .308" projectile. The neck area of the chamber will be loose if loading a GP90 in this manner, therefore cases will require regular annealing to minimize work hardening caused by expansion and resizing of the neck. Although a slow powder would seem the best choice as a means to minimize pressures, these burn rates can produce inconsistent pressure when down loaded. It is therefore wiser to use H4895 or N135 combined with .30-40 Krag data (similar case capacity and pressure rating), carefully working up to around 35 grains behind the 168 grain A-MAX / ELD-M, aiming for a maximum muzzle velocity of 2200fps. The A-MAX / ELD-M is a thin jacketed, soft projectile. This helps keep pressures to a minimum regarding the .304" bore diameter and in addition to this, the Hornady projectile produces broad wounding coupled with good penetration at low impact velocities. However before embarking on any such project, it is important to have a rifle of this age checked over carefully by a gunsmith. 
 
GP11 military ammunition uses Berdan primers. To reuse cases, primers must be removed hydraulically and replaced with new Berdan primers, a frustrating and time wasting affair. Norma and PPU brass is boxer primed and is therefore much more suitable for reloading. Some reloaders claim great success using .284 Winchester brass which has similar case dimensions however the rebated rim of the .284 is smaller than the GP11 and may fail to extract in some rifles. The GP11 cartridge does its best work when loaded with medium burn rate powders such as Varget (ADI2208) through to medium-slow burn rates such as H4350 (ADI 2209) if loading heavy weight projectiles.

The GP11 uses standard .308” projectiles, producing similar performance to very mild loads in the .30-06 or top loads in the .308 Win, therefore bullet performance notes can be sourced among these texts. Typical velocities to expect from the 25.6” barreled K31 without exceeding recommended pressures are 2900fps with 150gr bullets, 2750fps with 165 to 168gr bullets, 2600fps with 178-180gr bullets and 2400fps with 200gr bullets.
 

Closing Comments

 
The GP11 is certainly an unusual cartridge as are the Swiss rifles built to house it, its mention here is not only to realize its abilities as a hunting cartridge but also to bring to light the fact that it has been used extensively but discreetly wherever Swiss communities settle across the globe. One final note regarding bullet and barrel dimensions - these do vary. While I have tried my best to summarize measurements in a succinct manner, the reader should be aware that manufacturing tolerances were within a given range and that exact dimensions varied somewhat throughout the decades of production. 
 
 

Suggested loads: 7.5 Swiss					Barrel length: 25.6”
No	ID		Sectional Density	Ballistic Coefficient	Observed  MV Fps	ME Ft-lb’s
1	HL	175gr Berger VLD	.264	.528	2600	2228

 

Suggested sight settings and bullet paths
1	Yards	100	200	250	300
	Bt. path	+2.7	0	-3.8	-9.4

 

No	At yards	10mphXwind	Velocity	Ft-lb’s
1	300	6.5	2123	1751

Sight height 12.5mm (.5”) (military open sights)

 
 

	Imperial	Metric
A	.498	12.65
B	.497	12.64
C	30 deg
D	.457	11.63
E	.341	8.68
F	1.750	44.58
G	.334	8.5
H	2.180	55.6
Max Case	2.180	55.6
Trim length	2.170	55.3

 
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