Many servers block the use of .45 SMG weapon, but this video below shows that only a certain type of ammo (JHP bullets) can cause a bug where kills can be made through doors and objects.
By writing the following line in the server config...
ReplaceEquipment=SwatAmmo.UMP45SMG_JHP SwatAmmo.UMP45SMG_FMJ
...players are unable to use the bugged ammo and this hence turns the .45 into a normal weapon.