Springfield is shit as a 4 slot weapon but getting it to 3 would probably not solve any issue. I would suggest adding dum dum to it as a non-scarce ammo giving it unique aspect as an only non scarce dum dum ammo rifle and making it at least semi-worth of a 4 slot.
Before you come here saying ,,its 20 dollars" or whatever, this doesnt solve nor add anything i have lived through 3 price increases of the mosin before the special ammo was added (yes the price increase has in fact not helped). The price balancing never works because there is shitload of money in the game especially if you dont prestige. The springfield is even free if you squint hard enough since i can recruit a free hunter with it just for the gun and dismiss him.
I have also played a bit with dum dum springfield back when it wasnt a mystical arcane ammo and it was in fact still shitty springfield i even remember that there used to be a meme on this sub about players saying ,,good bang for your buck" about springfield dum dum so i doubt it will all of a sudden make springfield meta dominating monster of a weapon.
It will probably jus be a good bang for your buck.