Took my old Winchester pump out to shoot a few loads and check it out to see if it was still on............
Not.
It has been a while with lots of different ammo through it and I did not remember what it was sighted in for.

Started with a 40gr Lhp Sub-sonic load and it was quite loud for a SS load. It went across the screen at 1042 fps and all three were touching at 15 yards.

The 29gr lead short went across the screen at 691 fps and was a lot quieter than the 40 grain bullet but about twice the grouping.

The 29gr Long surprised me, only putting out 640 fps.
However it did group a little tighter than the Short...........the only problem is finding them.

CCI data has both 29gr loads rated at 910 fps.........which might be MV and not at 15 feet? Once sighted in the Long did well with a few odds and end 12 Ga. hulls, out at 20 to 35 yards.

Later.

I've chronographed many kinds of 22 ammo in a variety of handguns
and rifles over the years. Your sub-sonic velocity sounds about right,
they run a few fps slower than std velocity. The sub-sonic designation
comes from the fact that none will break the speed of sound resulting
in the sharp crack of high velocity rounds, not from very low muzzle
blast. Your 29gr loads read about what can be expected from CBs. Are
you sure that's not what they are? CCI makes both short and long
CBs, most companies don't. Most brands of shorts run about 1050 fps
from my rifles with CCI faster at about 1100 fps.