Any clues?

[Surpmil]

That photo has been discussed on other forums previously.

It is usually described as showing "Soviet Partisans" on the North West Front.

Some variation on the CLLE. The sling modification would be a very unlikely thing to be have done in wartime to rifles captured from the Baltic republics. That suggests either the rifles were ex-White Army and reworked in the 1920s or 30s, or else the modification was done by one of the Baltic republics in that period.

It would be an interesting choice if purchased by one of the Baltic states considering there were millions of surplus SMLE's in store after WWI. Was the heavier barrel preferred or just the lower price of the older rifle?