Flat point lead cast bullets work great for subsonic loads and are very cheap. At that low velocity they don't foul hardly at all and they stabilize easy due to there shortness in length and high density so you can use a heavier bullet As well.

The flat point will hit much harder than a fmj at those velocitys, and the lead will even expand a little bit. With a fmj you will only see similar preformance to a round nose 22lr and will likely over penetrate and the varmint will run a ways.

Just load it a hundred fps over the sound barrier and back the powder off .1 gr at a time u till you don't hear the sonic crack anymore then your good
To go.

I would advise against sub sonic fmj for hunting, but a 60gr flat point lead bullet at 1050fps will hit hard.

And it will sound like popping a bag of chips