Educate, educate, educate.
Chiefs are administarators first. They stay up at night worrying about what their troops are doing and whether it will get them sued or fired.
Our Chief is a great shot (probably better than most of the officers in the Department), is very, very pro-RKBA, and signs Form 4s. But he has those seemingly inherent LE Administrator fears when it comes to weapons, and many misconceptions. It has taken me four years to finally set him straight on the ballistic properties of .223, and he STILL doesn't want a general issue Patrol Rifle. I have more trouble getting him to sign Form 10s or Form 4s to register new MGs or transfer old ones from inventory than Joe Citizen does.
The best means is a long, slow education process, repeated often (the broken record theory of corrective discipline, stealing from the police administrators playbook) and documented thoroughly. Liability works both ways, and if you get shortcomings and deficiencies on paper often enough, the administrators stay up at night worrying about THAT.
Have fun, and I hope your Chief is a good sport.