For hunting and target shooting, air rifles have very little to recommend them when compared to firearms. There are so many problems associated with them, it's much more practical to get a .22
First of all, if the manufacturer says velocity is 1000fps, actual velocity will be closer to 850 because they test with the lightest pellets available and you will actually be using pellets that are suitable for hunting.
Second, dime size groups at 40 yards are possible, but they should not be expected. Even the tiniest puff of wind will dramatically open up the groups of a .177 When shooting a springer type air rifle, you need to hold it differently than you would a firearm. Just let the foreend rest in your hand. Hold the gun as gently as you can or the groups will be poor.
Air rifles are generally inherently accurate. If you are having accuracy problems, then switching pellets may or may not make a significant difference. Keep in mind that Gamo is the low end of the quality scale, and that the old maxim "you get what you pay for" definitely applies to air rifles.
Third, springer air rifles are heavy. Figure 8+ pounds.
Fourth, for the price of a marginal air rifle you can get a pretty decent .22 with a 4x scope.
I've used mine for hunting, but now I only use it for killing garden pests. The .22 is just much better in every way. With the low cost of bulk 22 ammo these days, 22 ammunition compares favorably in cost to pellets.
My experience is that the .177s are very effective on rabbits and squirrels, and do little more than horribly wound groundhogs. In any case, 40 yards is a very long shot for any air rifle of .177 and even .22. The projectiles are very light and lose capability rapidly.
Some people like air rifles as being good for indoor practice. That makes sense to me. I enjoy using an air pistol in my basement.