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Before I answered I had to look up the Savage 64 to discern action type. ie bolt, pump, lever, semi-auto.
Being a semi-auto that states LR it's possible that it's made to function reliably only with high velocity ammunition, BUT that being said you can experiment with standard velocity ammo in differing brands to see if the action will cycle them reliably. I'll go out on a limb and say sub-sonic and low velocity rounds would not cycle well if at all. I experiment with my .22 semi LR auto pistols to see what ammo they will shoot with reliable ejection and feeding. Shooting standard and low velocity rounds should not do any harm to the rifle, but you'll most likely have to cycle the bolt manually. You should also try several different brands of .22LR to test for the best function and more importantly the best accuracy in your rifle. It should handle HV 40 grain solid nose or 38 gr hollow points with no problems.