Stephen, just the bullet weight and ballistic profile. The 62 grain is heavier and longer. 55gr is on the left and 62gr is in the middle here : google.com/search?q=55+vs+62+grain+5.56&sxsrf=ALeKk00ekB7w2QnRPEA0HSPBbtLKAVyo0Q:1597689815354&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjJ3J6v8qLrAhWs2FkKHQCFDpgQ_AUoAXoECBQQAw&biw=1280&bih=590#imgrc=G9bcAC3gpmhNXM

It’s just the weight. If you do precision shooting then the grains will make a difference. If you just “plink” around then the grain doesn’t matter. It was my pleasure to assist you.

The weigh of the bullet in grains

62 grain is a heavier bullet. GR or grain is a measure of bullet weight where 1 grain is equal to about 0.00229 oz. Generally heavier bullets are less affected by wind and other environmental factors but also require a higher rate of twist in barrel rifling to stabilize them.