I believe it's a Chinese bam b3. It might also be a bam 40. I really haven't seen one of those for 30 years so I could be wrong. Does it have a sling mount on the side of the butt stock?
They were sold for around $15.00 - $20.00 a while ago and some stated they used theirs as a car jack.
If you get it for FREE then you won't be pissed.
If it has an oversized bore then the extremely utterly crappy oversized 7.9gr CROSMAN PREMIER SUPERPOINTS might work if NOTHING else you try shoots straight.
I had to go through a hell of a lot of these Chinese B3s over the years to finally get one that shoot good (I SIMPLY COULD NOT BELIEVE IT).
I gave them away for FREE (almost) just for the cost of shipping. This last one I will keep since it seems to be a real freak of nature totally uncharacteristic of them in the accuracy department. I would guess it's a 1 in 1000 chance in barrel lotteries based on how terrible my others shot.