Lightest Varmint bullet for a 1/8 .223 ?

I run 50 grain Nosler BTs @3180 in my 1/8s with 100% success. I could not get the 45s and 40s to hold together consistently unless I dropped the velocity down under 2900. At that point, the 50s were ballistically superior. I save the 40s and 45s for the .22-250 when I want a laser beam.
 
I run 40gr Vmax in a 223 1-12 at around 4000fps but as stated above you would have to slow them down a ton for a 1-8 or I don't believe they would hold together. 55 or 60 would be a better choice IMO.