Using a hand power grease gun is a great idea for this bearing. If any resistance is felt, stop. But since it rests in a partial spherical metal hub, the grease can, if the fit is not new and real tight, be pushed out between the hub and bearing. Also, if the anti-wrap system is worn and you have had the bearing wrap up in the past, the inner seal may be compromised somewhat. So IMO, if you get 3-5 pumps in and it comes up against resistance, stop there and perhaps make it an annual zerk. But if you get much more than 5, check where the grease is going by dropping the door under the feeder and check for grease around the bearing with a flashlight looking up into the anti-wrap window. IMO. If you see grease there, then perhaps make it a 20 hour zerk IMO.
On my 1680, the bearing to hub fit is quite good and the bearing is only 500 hours old. I get about 3-4 pumps into it at the start of each season and that's about it.