At the beginning of WWI the main idea in almost all armies was one of Napoleonic like battles of troops marching and and staring each other in the face shooting at each other. This idea made long rifles prevalent, making carbines nearly useless. By the end of the war trench warfare was the main idea now in the minds of military experts, especially the French. This thinking would soon be applied in the Maginot Line.
By the end of the war trench warfare was beginning to make the long rifle obsolete. The rifles were sometimes longer than the trenches were wide. This would seem to make the longrifle a thing of the past. However military thinkers of the time denied carbines, which would be excellent tools in the trenches, any kind of prominence. It would take 20 years before the Soviets would start large scale production of a carbine.
As said above, WWI also changed the markings on the Mosin rifles. At the beginning of the war the rifles sported two Imperial Eagles, one on the barrel above the date and Arsenal mark and one on the reciever, below the arsenal mark and date. In 1917, with the Czar shot and the Romanov dynasty fizzling out, the Bolsheviks began grinding off the Eagles. If a rifle is found with Eagles intact one should check for a boxed SA mark on the left side of the reciever, indicating Finnish service. If no box is present this means the rifle was very lucky and escaped grinding. during the Russian Civil War the Sestroyesk arsenal was burnt down, ending production of all military weapons there. The Mosin was used extensively in the Russian Civil War, being the infantry weapon of choice of both the Bolsheviks and the Whites. By 1924, with the Soviets in power, they turned to updating the M91.