Question: what is the difference between grain in ammo?
Answer: What's a Grain? Bullets are measured in a unit of mass called grains (abbreviated “gr.”). One pound is equal to 7000 grains, and there are 437.5 grains in an ounce. Bullets can weigh anywhere between 15 grains for the lightest 17 HMR bullets all the way up to 750 grains for the heavier .