Trying new loads in your rifle is always a good idea—you might discover that your groups shrink to a satisfying ragged hole by experimenting this way. But the cost of a box of premium ammo is significant. Here’s one way to vet whether a box is potentially worth investing in.

Concentricity Is Key
Good ammunition is concentric ammunition, meaning everything lines up and is manufactured with symmetry and consistency. One key example of this is the relation between the bullet and the brass. Ideally, the bullet should be seated so that it is precisely centered in the neck of the brass and isn’t canted to the side.

The degree to which a bullet isn’t centered is called run-out and can be measured down to the thousandth of an inch with specialized gauges.

But a quick and easy way to get a feel for run-out is to slowly roll ammunition across a flat surface, like a glass countertop. Do this while focusing on the tip of the bullet. If the bullet isn’t concentric with the brass, you will see the tip noticeably wobble. Ammo that does this is unlikely to shoot very well.

Perform this simple test before you buy ammo at the gun store to avoid spending money on sub-par rounds.