Romania had more than a million rifles in its inventory after World War One, but they were mused between Mannlicher 88/90, Mannlicher 95, Mosin Nagant, and Berthier patterns - and they were almost all rifles and not carbines. In order to make practical use of all these arms, it was decided to allocate them geographically rather than try to standardize on one single type. The region of Moldavia got the guns in 7.62x54R, including Mosin Nagants. This consisted mostly of M91 rifles, and very few M1907 carbines - but carbines were needed in fairly significant numbers to arm specialist troops (artillerymen, machine gunners, etc).

In the mid to late 1930s, about 10,000 carbine conversions were ordered, and these were about 2/3 completed by 1938 (the one date where we have an archival accounting of the project status). Presumably they were all finished before World War Two began. After the war, they remained in service as Romania continued to use 7.62x54R ammunition as part of the Soviet bloc.

The conversion process on these Mosins was more complex than on the other types of rifles that were shortened in Romania. The bolt handles were bend down, new rear sight leaves made (mimicking the M1907 pattern) and the original M91 rear sight blocks cut down to fit them. The M91 muzzle was removed, the barrel shortened, and the muzzle re-sleeved over the new end of the barrel to fit the original bayonet. And, of course, a sheet metal bayonet housing was added to the furniture to hold the bayonet when stowed.

These carbines are sometimes mistakenly identified as St Petersburg Cavalry School carbines (as in my own previous video on that subject).

Video on the Romanian Berthier carbine conversion from this same period:
https://forgottenweapons.vhx.tv/videos/romanian-berthier-carbine-4k

Thanks to the King Ferdinand I Military Museum for giving me access to this example and to A.N.C.A. for coordinating the visit! If you are in Bucharest, make sure to stop in and visit the museum:
https://www.muzeulmilitar.ro/en/