Consider placing a aluminum rod inside the
mag spring,
Likely a 1/8"diamter rod cut to allow five rounds.
I use a 60 for squirrel in SE MI, and I just load five, but one time ater quieetly walking a trail, and four yearling coyotes come tering out and away from me,
hunkered down to get a shot, when an adult made a "bark" and they skeddalled!
The I loaded all 18 forback-up.
MI regs do not mention rimfire, just canter-fire.