you can’t even “give” away a gun to your grandson...forbidden....
Not true. In fact there are many loopholes for "temporary transfers".
You can gift a gun to a close relative - but you may be right - not to a grandson. (So - gift to the dad that then gifts to the grandson).
However, if you want to go shooting with your son or grandson, you can’t loan them your gun at the shooting range! Gifts are okay, transfers (not just sales) are illegal.
But - like one poster said - who will enforce it? I suppose the gun range could be held liable somehow, and will be forced to come up with some way of enforcing it.