What type of structure usually backs target holders?

The correct answer is metal plates, as they are typically used to provide a sturdy, durable backing for target holders in air rifle shooting exercises. Metal plates are advantageous because they can withstand the impacts from projectiles without easily deteriorating or becoming damaged. They offer longevity and reliability, ensuring that shooters can train safely and effectively over time. Additionally, metal backing can help deflect or contain projectiles, reducing the risk of them ricocheting or causing injury.

While wooden boards, plastic sheets, and cardboard backing might be used in some setups, they do not offer the same level of protection or durability. Wooden boards can splinter and become less effective over time, plastic sheets might not adequately absorb or stop a projectile, and cardboard backing is generally too weak for repeated use in a shooting range environment. Thus, the use of metal plates stands out as the best choice for ensuring safety and effectiveness in target shooting practices.