I have data as low as 4.5 or 4.7 with Unique and a 124gr FMJ.
With these low amounts of powder I would use a 1.12 or 1.14" OAL to help with cycling and case ejection.
However 5.0 grs is my lowest for a 1.14" OAL with a plated RN for my pistols to have a good group.
Half of the art of getting a bullet to work is the amount of powder...........
the other half is the OAL with the different amounts of powder used.
5.3 grs of Unique can be a light load if you use a OAL of 1.169" if it will work in your pistol.
However you can save a lot of powder if you drop down to 1.12" OAL for light target loads.
As a note, a 115gr Berry plated at 1.10" will only hold 4.9 grs of Unique at 100% case volume.
A 124gr plated with a 1.14" OAL can hold 5.8 grs of Unique with a 100% case volume, with my dies and set up.
A OAL of 1.15" will be light in pressure with a loading of 4.8 grs of Unique.
Have fun.