Bobco,

If you are drastically off---hi/lo and/or right/left, you have a few options...

1) Yes, you can just manually adjust. However, I have found this to be quite difficult, as a turkey's head/neck are pretty small targets at 30+ yards as is, let alone remembering to aim 6 inches up and 12 inches to the left...

2) Better option may be to get adjustable fiber optic sights or a scope. Cheap red dots can be had for about the same as a good set of adjustable fiber optics (Tru-glo or Hi-viz). If you are experiencing a large amount of drift, with the majority of your target load, then I would highly recommend sighting one method or another. Overall, you're probably looking at ~$50...

Again, though, I would feel comfortable shooting what you have. BUT, if you could be getting 40-50 pellets in the head---compared to your current 5-10---at 40 yards, then your gun just became a definitive 50 yard blaster instead of a "gutsy" 40 yard gun.

If you have any more specific questions, drop me an email. I'll be glad to help ya' as best I can...