What is acceptable accuracy at 30 yards? Am I expecting too much?

Mike, yes, you should see better than 3/8 - 1/2 inch groups at 30 yards, assuming good conditions and good shooting technique. You mention that you expect one-hole groups only slightly larger than a single pellet hole, well, that probably crosses into a marginally unrealistic expectation, depending on what you mean by "slightly larger". When all is good, my rifles will certainly produce such groups, but not as an average. And frankly, after messing with these things 20 years, I would doubt anyone's assertion that such performance is average. One consistency I have found, flyers will occur, not a flyer off the paper, but one that stretches the group, maybe outside the group. That is just a reality of the technology. Your Daystate Wolverine hammer spring is not adjustable without some tinkering, but it shouldn't need it. I suppose that 910 fps is a bit hot with the 10.3, I would choose 880-900 in an adjustable rifle, but still, it should produce better accuracy. 
 
You may not have found the optimum speed for any given pellet. I agree with others, start around 875 ft per second, shoot some groups with different pellets then take the one that shoots the tightest and try adjusting the velocity up and down in multiples of 25 fps at a time and look for a sweet spot in velocity with that pellet. That is one method for you to try.

Single shot loading with a tray instead of a magazine will help you find out if there's any improvement there or anomalies introduced by pellet travel through the magazine. Also inspect your crown very closely for any lead buildup or imperfections.

And yes, because pellets are slower, follow-through after the release is important. The guns frame will move a little before the pellet leaves the barrel. Finding and maintaining the right shoulder pressure can help, as you discovered.

Good luck, let us know what you find.
 
As someone else suggested. Try a different scope. I spent the last year dealing with a brand new gun and brand new scope. And not being able to get good groups at 30 yards. Due to a wondering zero. I finely swapped out the scope for a known good one. And the gun shoots fantastic now.

Another really relevant aspect to get accuracy is try to have the face and the eye allways in the same place and angle in regard of the scope.

Having a really good scope is not a matter of price nor a manufacturer. My must reliable scope for hunting with my .357 is a very cheap one. But has proveen to keep the zero under all circumstances. I am certain that at 50 yards I am going to place the 81.02 grain pellet exactly where I want.

Another topic that should be taken into consideration is that the scope is permanently in the "zero" when and just when, the reticle is "resting" where it has to be (adjustments within the reticle of the scope is a matter of internal tensions) . Small adjustments along days or weeks could be needed to achieve that.
 
Sometimes when I shoot pellets too fast they start to weave around and spiral, I have seen it in the sunlight from a scope. Like anything else in physics I guess they get unstable over a certain speed/spin threshold.

Also when I shoot off a bench (which is just about always nowadays) I kind of let the weight of my forehand pull the gun down a bit tighter into the rest and try to do it the same weight/tension each time. Made my groups much better (when I remembered to do it, that is).
 
Scopes have been mentioned a couple times in here. I’ve had several Daystates and all were capable of ragged one hole groups at 25 yards. Being an unregulated rifle shouldn’t make any difference that close. 


One thing to check is the parallax on your scope. Make sure you are paying attention to that. I had a buddy who threw a Nightforce scope on his Wolverine and couldn’t figure out why his groups at 25 yards sucked. But the rifle shot very well at 100. The reason was the Nightforce had a minimum parallax setting of 50 yards and he was getting significant parallax error inside that distance. A scope swap and the rifle was a hammer at all distances.
 
Sometimes when I shoot pellets too fast they start to weave around and spiral, I have seen it in the sunlight from a scope. Like anything else in physics I guess they get unstable over a certain speed/spin threshold.

Also when I shoot off a bench (which is just about always nowadays) I kind of let the weight of my forehand pull the gun down a bit tighter into the rest and try to do it the same weight/tension each time. Made my groups much better (when I remembered to do it, that is).

I learned that a firm preassure on the forehand helps a lot to increase accuracy.

Depending on what you are resting on, it is easier or more difficult.

When shooting form the window of the SUV I have not found the way to do it yet.