Brackets for Live edge wood shelf

A wooden shelf that is cantilevered 3 inches or so out from the end of a bracket will probably survive some load. But stack too much of a load on it (a pantry, canned food is heavy!) and even wood will crack. Particle board is very likely to fail of course as it has very little real strength.

A shorter bracket will often be designed for a smaller load. (Long brackets may be wider at the base, to support a larger load. They may be more robust to prevent buckling.) The issue is not just will it support the entire width of the board, but is the bracket adequate to support a greater load since a wide shelf will have more items stored on it. Those extra items stored are hanging a significant distance away from the wall.

The biggest problem with heavily loaded triangle brackets on drywall is that drywall material is not strong enough to resist being crushed by the lower end of the bracket. You will need to support the bracket with harder material.

If you have a hole saw, cut some disks from hardwood or similar material the thickness of the drywall. The exact diameter of the disks is not important but should be about 1" to 2.5".

Make sure the brackets will be aligned with the studs. Mark the positions of the lower fasteners on the wall.

Use the same hole saw to cut openings in the drywall, over the studs, where the lower fasteners would punch thru. Plug the holes with the hardwood disks. Spackle and paint as desired.

The hard plugs will resist the force exerted against the wall by the lower ends of the brackets.

You can also back up the upper fasteners in the same way. This will resist wall damage from anything crashing into the edge of the shelf. It will also make the shelf installation easier.