74?? You say "was" - was that when you still had fingers & the rifle wasn't in twenty pieces?
Without even digging out the reference books I'd say that is a VERY compressed load = maybe 47 would be closer (again, without checking ANY books - so DON'T use that as load data!!)
7,62x53R is not basically the same, it IS the same: The actual case length for both is 53.5mm - the Finns went down to 53, the Russians up to 54...but it's the same ammo.
The FIRST true Finnish made Mosins pre-date the Winter War by quite some time, at least 15 years....as a lot of the M91 rifles seized from the Russians/Soviets in the 1917 Independence War & the Bolshevik uprising were rebuilt in the early 20's - the first true Finnish rifle being the M24 = nicknamed the Lotta rifle as the female Lotta Svard raised the funds to have the work done. (They were a like a cross between the Women's Institute & the TA)
The Finns had two main factories to do the rifle upgrades & new builds. State Factory 1 & Home Guard Factory 1; these would in turn change names to, SAKO and TikkaKoski (meaning Woodpecker Rapids, after the location). The other factory at VKT eventually morphed into its current entity, Valmet. All three still well known makers of high quality products.
My Finnish rifles tend to slug at around .3095" - and most of the Finnish reference books DO state that the nominal bore dia of Finnish barrels is .3095"
Even my M91B with a Belgian made barrel slugs at that size.
THE official issue bullet of the WW2 Finnish military is still in production too - the Lapua D46
Tracer? The Finns bought some 10 million or so .303 tracer as WW1 surplus from us - this was in turn pulled apart as a source of powder - and the .330 tracer bullets were used to make 7.62x53R tracer ammo. Not too big a departure from the big scheme of things as the UK made a lot of 7.62x54R ammo in WW1 & WW2 for export to Russia, etc. Greenwood & Batley being possibly the biggest supplier, but Kynoch & others make it too. @SPARKIE
If you have not done so, try to do a bore slug to confirm dia.
Also, check out "the load" information online - for most military .30-cal or similar, you use a lead bullet of standard weight & either 16gr of 2400 or 13gr of Red Dot. Good for up to 300m or so.
If your Mosin is a newer one or a Soviet, you may be better trying a Lapua of bigger dia or the Sierra Match King or Game King .303 bullets
Best of luck with it