I have a Lee Double Cavity Mold Ctl312-160-2R which produces 160gr 7.62x39 boolits. What Lee sizer do I need to reload for an AR15 in 7.62x39?

I have the same mold. I use the .311 sizer die and it works great.

slug the bore/throat area, then size .001 larger, as long as it will chamber, should be good to go.

Try is as cast, and lubed. It may work just fine.

Look up, and do a "pound cast" technique to get an accurate measurement of your chamber throat. Ideally, the bullet should juuuuust slip into the throat ( ie 0.0005" smaller that throat diameter) .

Try some Lee liquid lube. May have to lube it twice.

If you don't have to resize, and can get away with a single Lee Liquid lube application, you will have a simple, low cost cast bullet shooting system. If you need gas checks, ( for MV over ~1200 fps )then you need some toys. Might be able to use a Lee push through sizing die and push through a gas check to seat to the bullet. May have to open up the push through die to the throat diameter ( or see of Lee makes custom push through dies to your desired diameter.