The original Mosin Nagant was the M91 as in 1891, made until the 1920's. The spike bayonet is almost 20" long
They are 51 inches long overall with 31 inch barrels, weighing 9.6 lbs.
There were shorter M91's made to be easier handled on horseback. The Reds developed these into the M91/30, which has similar dimensions.
The Soviet improved standard was the M91/30 with better sights and bayonet attachment.
It is 48.5 inches long with a 28.7 inch barrels and weighs 8.7 lbs.
The M38 carbine was for support troops who didn't shoot as their first duty.
Similar to the M91/30 but 40" long, 20" barrel, 7.6 lbs and no bayonet.
The M91/30 was still unwieldy in house fighting and the M38 had no bayonet(handy when bumping into the enemy coming through doors or around corners.)
The M44 is like the M38 but has a 15" folding bayonet hinged to the right side of the barrel.
M44's are 40 inches long overall, barrel is 20 inches and weight is 8.9lbs.
The Finns had a few models of rifles, most are rare except for the M91s and M91/30s they got and rebuilt in varying degrees, and the M39.
The M39 is a Finn design based on the Russian receiver. It handles and shoots well, and most Finnish rifles will have better quality and accuracy than Russian or Soviet ones.
The M39 is 46.6" oal, 27" barrel and around 10lbs.
For more information see these sites:
http://www.russian-mosin-nagant.com/
http://www.mosin-nagant.net/
HTH,
Mike