and you are right about the Industry B-4-1, it is very low powered in .22 cal.. Actually I sent away for a .177 cal. B-4-1, but the warehouse sent me a .177 cal. box with a .22 cal. B-4-1 inside. I bought one of these B-4-1s for the shop for selling because I liked the looks, thought it could be a good seller, but after trying it and realizing how low power it was, I never bought another one, I never even bothered to send away for the .177 cal. model after this dissapointment.
Believe it or not, a friend of mine liked the looks also (B-4-1), he tried it and bought it as a gift for his father in-law at a discount price (cheap) I gave him. His father in-law started complaining about the low power. Later on I bought a few of the XS B-7 models, much more powerful than the B-4-1 models. About a year later, this friend of mine got tired of hearing his father in laws complaints about the B-4-1 and bought one of these B-7 models for his father in law for Christmas and his father in law loved this model, no more complaints.
The reason for the difference in power between the two models is that the XS B-7 comes with a leather piston seal and a better main spring. Lubed leather piston seals work great in .22 cal.. The B-4-1 comes with a syn. piston seal, these work ok in .177 cal., but don't give much power in .22 cal., leather seals work better in smaller .22 cal. air guns, syn. seals don't. This is why all of those cheap Cummins air guns only come in .177 cal., most of these models come with syn. piston seals.
The B-4-1 I tried was giving even less than 500 fps in .22 cal. about 480 fps. The B-7 I tried gave over 700 fps when dieseling (first 4 shots) and settled down to 650 fps. Of course leather seals need lubing more often, I use Slick 50 on this model, I recommend 3 drops every box of pellets. So you can expect about 150 fps more from this model easily.
All XS B-7s I bought sold fast, everyone who tried it liked it. Here is a little review I did on this model.