To get the lucky s barrel youll need to do a series of task.You need to get card keys in order to get this lucky S barrel which increases the experience you get.
1-Shoot the rusty pipe on top of the laser door which has the elixor.Shoot the canister that is there to get a card key.
2-enter the tunnel in that same area and shoot the explosive ball canister on the celiling near the blue light to recieve another card key.
3-follow the path to the gun turret near the mako point and use the gun turret to shoot the crane off the ledge to the south.Return to the crate that fell to the ground and shoot it to get another cardkey.
4-There is a laser barricade close to the barricade which you found the elixor.Use one card key to deactivate it and retrive two card keys.
5-proceed through the sewer tunnels to the ladder leading up to the clearing in the norhtwest.Jump back down the ladder chute to pluck the cardkey out of the air.
6-Climb up the two ladders to the room which the shop and locate the cardkey behind the shop.
7-Smash the crate that is near the shop to get another cardkey.
8-Drop onto the ground to the northwest of the shop and carefuly crawl to the cliffs edge.There is no way back up if you fall down to the lower area,so font fall!Now manuever the camera for a better view and get the cardkey thats on the hedge I mean Edge.
9-you should have nine cardkeys.Return to the sewer tunnel and approach the area with the numerous barricades of laser in a row.Use all card keys to gain at the end the lucky S barrel and two more card keys.
10-climb the ladder to the room where the turret gun is and use a cardkey on tha barricade there to get bayonet rifle.
11-Return throuhg the tunnels at the beggining from the canyon and use a cardkey to get Elixor.
12-Continue back trough the tunnels to the last remaining barricade and get the limit braeker.