I used the Omochao gun for 1:47. Come to think of it, though, the Shadow Rifle is probably about as good for this level. I suppose I'll briefly explain what I did:
-I miss the first gong by avoiding the center of the target. I homing attack one of Eggman's robots twice, and grab its gun. I then shoot up the robot on the ball so that I can proceed.
-Skip to the part with the first GUN robots... after bouncing up out of the tower, I shoot the first beetle (1), then I homing attack through the other beetles (2, 3, 4), and the ring container afterwards. Then I get onto the ride.
-After the ride, I shoot the special weapons box in front of me, and I switch to the Omochao gun. I go left and fire 3-4 times to make sure both the beetle (5) and the mech (6) are destroyed.
-Next, instead of using the rocket, I take the low road. I fire at the mech (7) at a slight angle so that the bullet destroys it, but doesn't go for the beetles ahead. I need to use homing attacks on the beetles (8, 9, 10) to proceed quickly. Then, I run between the two Eggman robots and light dash to get to the slide.
-Skip to the second gong, which I again purposely miss by hitting the side of the target. I fire at the beetle (11) and hope that the bullet bounces over to one of the mechs as well; it's usually the one on the right for me (12). I then shoot the other mech (13) while running to one of the springs ahead.
-After the next stretch, I take the low road, where the mechs are. I shoot the next mech (14) while running to the opening in the floor, then I jump down and avoid the pole. After landing, I shoot the mech (15) and proceed.
-Skip to the tightrope. As I slide off of the tightrope, I fire madly at the two beetles, since I have infinite ammo at this point (16, 17). I hope that I get them quickly so I can land right onto the spring. Then I grab the rocket and let go of it as soon as possible. I drop down and shoot the mech there (18), then I proceed to the last two mechs...
-When I get to the part with all the crates, I just fire madly to take out the last 2 mechs quickly (19, 20).
Hope that helps somewhat. If further explanation is needed, let me know.