It's not the weight of the bullet but the volume of gas that causes problems. If this is a pistol can it will work with all subsonic 45 colt loads. If it is a machine gun can it will likely work with all 45 colt and 44 mag loads. So just shoot subsonic or near subsonic and you will be fine.
Make sure the guy who threads your rifle's barrel cuts the threads on a lathe. They have to be perfectly concentric to the bore.