There's not many people at all anywhere hunting pigs at 300 yards. I'm hoping the op is just wanting to spot them out to that range to set up shots at a closer range. I won't judge though.
Another suggestion, since the farm fields are already a dug-up mess,, OP needs to get his hands on a M79.. Night vision scopes then will not be an issue, or 300 yard targets
e10 throws even farther than 300, it is small and light. comes in green red and white, outside diameter of a battery tube is 31mm, a 30mm scope ring can be used to mount it on a rail, with minor trimming. however i'm not sure how it will handle the recoil. especially solder points in the driver
there are also green target illuminators, made specifically for mounting on a rifle, but they are much more expensive.