This may be irrelevant since the FTF problem also appears on brand new 93s, by I have noticed leaving a rimfire rifle cocked will, over time (sometimes very little time), weaken the spring. When putting it away, always open the bolt, double check for a round in the chamber, empty the mag, depress the trigger and close the bolt. NEVER dry fire any rimfilre rifle.

As a side note, I just bought a new 93R17FV, and with just under 50 rounds thru it, I have had no misfires. I did notice that the indent on the cases was rather shallow, so a new spring may well be in my future as well.