I would disagree with those who opine that ALL Gamos are junk! I just replied to another thread, and my response here will be pretty close to the same, but I have two Swarm Maxxims in .22, and my neighbor has one in .177. All are capable of putting pellets in the same basic hole at fifteen yards. I will state that the very first thing one should do when getting one is thoroughly clean the barrel. I used a bronze brush first, then followed up with Hoppe's #9 on several patches, then clean patches. #1 rifle was absolutely a mess inside, #2 not so much. But I cleaned both before I shot them, and this was because I saw a video review which brought this to my attention.
Secondly, one must experiment to find the right pellet for the rifle. I found two early on that worked extremely well. I first discovered the Gamo Rocket, then found the JSB Exact Jumbo Heavy 18.3 grain, and that's where I stopped! The rifles all like to be held firmly, instead of in the 'artillery hold'...and I shoot off a tripod. My trigger elbow is braced on my chair, and this sort of shooting position triangulates everything. If I don't use this hold, my shots are all over the place...same thing for my neighbor who poo pooed my idea...until he tried it, and LO! It's a miracle! His .177 isn't quite as accurate...that could be him, or it could be that he buys any old pellet from Walmart and doesn't put any thought into pellet choice. He shoots good groups, mind you, much better than those indicated elsewhere in this thread.
Before I bought my first Swarm...I have two because I bought another after somebody tried forcing a .177 magazine into my .22...I did some research, and what I found that although some complained about inaccuracy, most folks said the opposite. I've been VERY satisfied with my Gamos, although I'll admit that they are not the end all to beat all...for me, that would be the Air Arms TX200 Mk III, but that's up the road.
So, if you're having accuracy problems, I'd suggest cleaning the barrel...find the right pellet...discover the correct hold for your rifle...and take your time when you shoot! Works for me!