A 1918 as well, lucky you. I undestand that some of the 1917 were turned into straight pull rifles.
As far as clip development;
From; Berthier Rifle and Carbine
http://www.virdea.net/french/berthier.html
(14)The Berthier was tested in 1889 with a wide range of magazine capacities from three to six rounds. The three round capacity was chosen after testing by soldiers - it was handier, did not catch on clothing, and it was still faster to shoot than the Mle 1886. When the weapon was used for cavalry or for volley shooting the three round capacity was sufficient, but in no-man’s land the smaller magazine capacity was a real detriment. A five round magazine put it on par with the Mauser 98 rifles in use by the German infantry. (return)
From;
http://ww2.rediscov.com/spring/VFPC...g/DETAILS.IDC,SPECIFIC=12784,DATABASE=objects,
At the bottom;
"During the First World War the limitations of the Lebel design became ever more apparent and in 1915 it was decided that the 1907 Berthier rifle should enter mass production as a partial substitute, being known as the Fusil Model 07/15. The design was modified in 1916 in order that a five-round box, which would be more suitable for use in the trenches, could be fitted. Manufactured on a large scale fo
References:
Bruce, Anthony. AN ILLUSTRATED COMPANION TO THE FIRST WORLD WAR. Michael Joseph LTD. London, England. 1989.
Walter, John. RIFLES OF THE WORLD. DBI Books, Inc. Northbrook, Il. 1998.
From “ 151 RIL, Regiment d’Infanterie de Ligne “
http://www.151ril.com/content/weaponry/firearms#Berthier 2
· First examples produced: Sept. 1916 with the design approved in Dec. 1916
· First distribution: Spring of 1918
Page also has information on the R.S.C. model 1917, or F.A. 17 (8 mm)
and shows a partial picture of the clip.
Further reading;
https://en.wikipedia.org/wiki/Berthier_carbine
Carbine Mle 1892
Changes
· Magazine expanded to hold 5 cartridges (1916)
· Rear and front sights added (1920)
· Built-in cleaning rod removed (1927)
· Modified for the 1932N cartridge (1932)
· Modified to stripper-clip and the 7.5 mm cartridge (1934)
The most successful and long-lived variant of the Berthier system was the short and handy carbine version of the five-shot Mle 1916 Berthier rifle, designated "'Mousqueton Berthier Mle 1892/M16". Contrary to the Mle 1916 Berthier five-shot infantry rifle whose manufacture had barely started during the late summer of 1918, the mass production ( over 800.000 "mousquetons" ) of the Berthier Mle 1916 five-shot carbines had begun much earlier, in May 1917, at the Manufacture d'Armes de Chatellerault (MAC) . The Berthier M-16 five-shot carbine immediately proved to be very popular with mounted cavalry, artillery, and reconnaissance troops. It was still in service with some French law enforcement units as late as the 1960s.
Based on the preceding and the slowness of Governments to adopt a new weapon feature I think it is safe to assume the 5 shot Berthier clip was around long before 1916.