That's generally the case, but not true here. 49 CFR § 1540.111(c)(2)(iv) requires that when firearms are transported in checked baggage, "only the passenger retains the key or combination." TSA approved locks are not allowed here because by their very design, the TSA retains a key to the locked luggage. That's why when traveling with firearms, you'll either need to wait by the bag drop for 15 minutes in case the TSA calls you to unlock your bag or you'll have your bag inspected in front of you.