I really don't think this gun is suitable for 40-50yd hunting in stock form. Birds (not crows) yes, but squirrel and other varmint, no.
When I get it up to 700fps with the hammer spring mod & 9oz CO2 PB bottle, then I can see doing some 40yd hunting, maybe even 50yds. It should have around 7-8fpe left in it at 50yds with a CP. The important thing is to use pellets with a high ballistic coefficient like the Crosman Premier and JSB pellets like the Express 14.3gr. The JSB Jumbos 15.8-16.0gr are a little too heavy for the 850 and don't fit in the loading port too well. The Superdomes and FTS that the 850 really likes don't hold much energy passed 25-30yds. At 50yds the CP retains 50% more energy than most other pellets! as does the Kodiak but 21gr is too heavy for this gun.
Also the problem with 50yd shots is that a head shot is very difficult. You are most likely going to go for a vitals (body) shot and the chances of the animal getting wounded and escaping are greater. I want to make sure my quarry goes down fast so I don't risk shots like that unless I use a 20+FPE Springer. They have plenty of power for a quick kill @ 50yds. My 350 .22 has 14+FPE left at 50yds with a CP so theoretically I could take prey at 70yds and beyond, but gravity, holdover, wind, and everything else comes into play with great distances so chances are the shot will not be too accurate. My longest shots I made with the 350 were at 45yds - a groundhog and a crow, and a couple of squirrels at 40. All went down fast and the same as the 25yd kills, but I 'm limited to about 50yd shots only on my property. When I get a scope on the 350 (soon after a tune) I will not hesitate shooting at 50yds. My guess is after I tune the 850 for 700fps or 15.5-16fpe, I will probably limit my shots to around 40yds. Mainly because I trust and know the 350 will take game easily at anything >40yds.
The good thing is that with the .22cal. 850, or any .22, your 1-shot 1-kill ratio is greater than if you used a .177, so that's another plus on top of the increased energy.