I sighted them in at 950fps out of a Maverick Compact at 50 yards. They really did well. I think they are NSA .217 20.3's but not 100% sure. I've heard of other guys shooting them as low as 800fps out of Daystate Reveres, but maybe I got lucky as my first dial-in at 950 was dead on 1/2 or better at 50. I didn't try any other speed.
These are in fact produced by NSA to sell through Daystate. Nick sells a similar slug directly that I believe is just a few grains difference. They really do work wonderfully in a variety of airguns and yes, they can perform well in even some lower powered ones. These in .22 produce about twice the BC of the JSB redesigns. If anyone is on the fence about giving slugs a try I would highly recommend these.
I set an email to Nick telling him I was having issues finding the Howlers in 22 cal. He said the 20.2 grain .217 diameter were the exact same. In my air wolf I tried the .216 20.2 grain and they shot well, the .217 Howlers shot well but were tight fitting. I was experimenting with speeds from 880-920 fps. 905 to 910 fps seems to group the best. My next order will be the .2165 in 20.2, like Goldilocks I'm hoping these will be just right!
I shoot them out of a MKll Impact compact at 900 fps, and they are bad medicine on pest birds, squirrels, and a few groundhogs. Furthest shots have only been approx 75 yards, but they work just fine for my uses.