Now, before I continue I would like to be clear that I don't know all there is to know about Finn slings. What I've learnt has come from reading and participating in various forum posts, looking at various websites, corresponding with Finnish collectors who have local knowledge, and trawling through the SA-Kuva photo galleries. Unfortunately there isn't a whole lot of primary source info available to us in Finnish, let alone English, but I'm sure some will be found in time.
From looking at SA-Kuva we can see that whatever sling was handy was used, so technically if it fits it is correct for your rifle regardless of type. Please note how largely I haven't said 'this is for an M28 or this is an M28-30 sling' as I don't believe slings were categorised this way - I believe that before 1941 you had Army sling types to go on rifles in Army inventory and Civil Guard sling types to go on Civil Guard rifles, after 1941 all bets are off and whatever is available is correct.
Here we go....
Civil Guard sling brown leather with riveted steel oval buckle - marked 'SY 1924' 54 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4570_zpsqtyi0ufz.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4571_zps70o2m8q2.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4572_zpsajvbpqlr.jpg)
Civil Guard sling brown leather with sewn German Silver(?) 'squarer' oval buckle marked 'SY 1925' 54 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4574_zpsbke4znjt.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4575_zpsdsgpdcyy.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4576_zpsjc8tirhn.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4577_zpsra7ut4c4.jpg)
Civil Guard sling brown leather with riveted German Silver(?) 'squarer' oval buckle marked 'SY 30' (hard to see in the photos) 54 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4578_zpsplfrs7l8.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4579_zpstnhondmb.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4580_zpsgwc5iyhl.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4582_zpswzfij6kb.jpg)
Army sling brown leather with riveted rectangular steel buckle. Also found in green leather perhaps the most common Finnish sling 1939-45? 53 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4583_zpstd2y5vz0.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4584_zpsidhefy2e.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4585_zps5qemwu15.jpg)
Not REAL sure about this one, has been referred to as a 'Continuation War m/28 sling', but some Finnish collectors tell me it may be an early 1930s web sling intended for Civil Guard rifles. Thin tan web with German Silver buckle. 43 inches long (short?)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4586_zps2wvixrsk.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4587_zpsspu6br3n.jpg)
Civil Guard Depot replacement sling. Tan web with brown leather tab. 'Sk.Y' marked. These can be encountered without the CG mark, these are considered to be private purchase slings made by the same company. 49 inches long.
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4588_zps3o1noown.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4589_zpsnqiyguss.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4590_zpsu0vngete.jpg)
Army "M39" sling. Green leather with zinc(?) rectangular buckle. May be post-war. 49 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4591_zpsqyvug7ky.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4592_zpstgmurh59.jpg)
Army 'M39' sling. Green Leather with reused steel oval buckle from earlier sling. May be post-war. 49 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4594_zpslihgyxxq.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4595_zpsto9t4neu.jpg)
Army(Airforce? navy?) 'M39' sling. Grey leather with zinc rectangular buckle. Post-War. 48 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4596_zpsfp72xr5p.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4597_zpswbnk2x7w.jpg)
Rubberised canvas 'tractor belt' sling. One end riveted together, the other with sling button. Made from grey rubberised canvas, this one is missing its keeper. 50 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4599_zpsxzhwpspf.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4600_zpsredrqbwi.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4601_zpsxvu6g9ns.jpg)
Rubberised canvas 'tractor belt' sling. Both ends with sling buttons. Made from orange rubberised canvas. This one is unissued. 50 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4602_zpszjepqsel.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4603_zpsdklxbzca.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4604_zpsotyj9wgo.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4605_zpstb32pqbp.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4606_zpscvhcm4vs.jpg)
Late Continuation War depot replacement sling. Made from green web with steel rectangular buckle. Many different coloured leather reinforcing pads available. 48 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4607_zpsto2cfwfk.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4608_zpskoqzkuzx.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4609_zpsrqjgqbgj.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4610_zpsnpjharqo.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/Finnish%20Slings/finnwebendsGB.jpg)
Late Continuation War depot replacement sling. Made from green canvas with a reused German Silver squarer oval buckle. 46 inches long
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4611_zpsk9rg1jjn.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4612_zpsmrz7tcgu.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4613_zpspd8lzjvu.jpg)
Civil Guard two piece 'M30' sling. Steel wire roller buckles. Also an oval buckle version out there. Long section is 45 inches long, short section is 12 inches long. After the war the Army removed the short section from these slings and issued the long section only.
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4614_zpsoabttprb.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4615_zpss4o5wqgt.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4616_zpscrbeg359.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4618_zpsla6mdb2f.jpg)
Italian Mannlicher Carcano Sling. Brown leather - not too many variations of these....
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4623_zpszdgegcg9.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4624_zpshy011pbw.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4625_zps5bzut31n.jpg)
Finnish Captured Soviet SVT38/SVT40 sling. Another variant exists using a smaller trapezoidal buckle.
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4627_zpstgr6gxpa.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4628_zpsil3twhse.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4629_zpsnacocgnn.jpg)
Finnish Captured Soviet M91/30 sling. Fairly common, with some 'ersatz' variants being found.
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4630_zpssofgkoc3.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4631_zpsvoz48xhe.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4632_zpsbvzzvyyi.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4633_zps5nepzqz6.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4634_zps0qjywurr.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4635_zpspa8ute9y.jpg)
![Image](http://i137.photobucket.com/albums/q209/fernleaf78/RMN/IMG_4636_zpsqoey4505.jpg)
There are a few different variants of Finn Mosin slings that I'm missing - I'd love to see what slings some of you guys have?