Get at least ten fifty-round boxes of different ammos, standard velocity and high velocity. This is a one-time investment that will tell you what you want to know. None need be the very expensive match ammo. Try some cheap stuff, but get good quality ammo as well, like CCI.

Take your time and shoot ten-shot groups on a calm day. 100 yards is stretching the potential of the .22 LR anyway, and just a little wind will prevent you from assessing the accuracy potential of whatever ammo you are shooting.

You often get what you pay for. To spend a little more for good quality accurate ammo is well worth it rather than spending a little for trash.