There are several types of steel used for target construction. Depending on the brinell, or hardness, steel is suitable for different types of targets:

Definition of brinell (from www.merriam-webster.com):

: the hardness of a metal or alloy measured by hydraulically pressing a hard ball under a standard load into the specimen

A36 or mild steel - has a brinell of150-180. It is a low carbon steel that is not heat treated. We use mild steel for our smallbore silhouette targets: it is suitable only for .22 calibre at prescribed distances.

AR225 - Abrasion resistance or AR225 has a brinell of 225. High carbon steel, not heat treated. We currently have no targets utilizing AR225

T1 or A514 - a heat treated alloy with a brinell of 235-300. A heat treated alloy suitable for standard velocity rounds. We currently have no targets utilizing T1/A514

AR400 - Abrasion resistant or AR400 has a brinell of 370-470. A heat treated alloy suitable for most rounds, depending on distance to target. Our small swingers, poppers, and our silhouette targets utilize AR400.

AR500- Abrasion resistant or AR500 has a brinelle of 470-521. Armor plate, heat treated alloy is suitable for most rounds with the exception of armor piercing ammo. All of larger swinging gongs, ipsc targets, and super duty type gongs utilize AR500. Our .338 Lapua target also utilizes AR500 for the stand upright.