I drilled a hole into my drywall and hit a metal stud. I don't have a drill bit for metal. I have 5/16" plastic wall anchors that will hold 85 lbs in drywall. Can I cut the plastic anchor so it's shorter in order to fit in the hole where the stud is? I only have a 24" wide space to put up shelves and I tried drilling 2" to the right of each hole but I'm still hitting the stud. My 22"w shelf installation bracket needs a hole on either side and one in the middle. The one on the right is fine. The middle and left are hitting studs. The bracket is centered so there is a one inch clearance on either side. My studs clearly aren't spaced properly. This horizontal bracket will hold 2 vertical brackets, which will then hold 4 shelves. If I cut the anchors, I'm afraid it won't be strong enough. I only have 1/4" drywall. Can I cut the anchors? Or does anyone have another suggestion. I need to use this space for my shelves. I can't use another wall.
Shelves hold loads eccentric from the wall, causing the upper fasteners to work in tension to keep things stable. When your drywall fastener says that it's rated for 85 pounds, this is probably 85 pounds of shear when anchored in 1/2" drywall and for items that cling close to the wall like mirrors, pictures, etc. Quarter inch drywall implies that you're probably getting 42.5 pounds of shear strength with your fasteners. For tension, the strength rating will be smaller that the shear rating if there's even a tension rating for your fasteners at all. If you can't find a positioning that puts all three anchorage points on studs, then I would probably drill a new hole through the horizontal bracket that aligns with the stud. Without seeing the actual shelf, I can't say for sure.
If you hit metal in a wall, then your first instinct should be "I just hit a protection plate," where these plates exist to protect plumbing, electrical wiring, and gas lines from screws. I don't want to be responsible for somebody puncturing a gas line, so please, please, please verify that you're not drilling through a protection plate.
If you have metal studs, however, then you want self-drilling sheet metal screws. These have a drilling tip intended for cutting a pilot hole for the sheet metal screws to follow (see below). One of their virtues is that these screws would take a tremendous amount of effort to puncture a protection plate--sorry for carrying on about those. Self drilling screws include the self drilling tip in their named length, e.g. 3/4" screws would be too short for a 5/8" total thickness application. For your screw lengths, I would add 1/2" to your total thickness to get a few threads through everything (your total thickness includes your metal stud, the drywall, and your shelf bracket--no protection plate in there).
Here's what those screws look like, although you can get different driver types: