I wouldn't worry about a 20 inch barrel , you will not gain that much velocity in 2 inches
today I would get this https://palmettostatearmory.com/psa-16-5-56-nato-1-7-mid-length-nitride-13-5-lightweight-m-lok-moe-ept-acs-l-rifle-kit-w-nibr-bcg-flat-dark-earth-5165449482.html?trk_msg=26A7FMVUVUBKN4746HA0F3HA4S&trk_contact=A06J51OOFOLT0KCKBQFVKGHB7O&trk_sid=6BP177703DM550FHEGQ4LMN5MS&utm_source=Listrak&utm_medium=email&utm_term=https%3a%2f%2fpalmettostatearmory.com%2fpsa-16-5-56-nato-1-7-mid-length-nitride-13-5-lightweight-m-lok-moe-ept-acs-l-rifle-kit-w-nibr-bcg-flat-dark-earth-5165449482.html&utm_campaign=Daily+Deal+Email&utm_content=12%3a00+Email
it is a nitride barrel , free float has sights s you can shoot it as soon as you get it
changes I would make , a set of reduced power springs
https://www.midwayusa.com/product/579878...b-reduced-power the kit already has the PSA enchaced trigger which is better than nothing but improves more with a set of springs
my choice for the day wilL depend on the deal that day
but they will all be free floated mid length gas system
it will generally be a Nitrited barrel but depending on the price I would go stainless , Mennonite or if really low cost just plane old chromoly steel and figure shoot it out and buy a better barrel later
1:9 1:8 1:7 unless you specifically plan to shoot heavy bullets all have shown the ability to shoot 55gr decently.
by the time you get a that kit and a PSA stripped lower and a set of springs and a transfer fee on the stripper lower your probably about 475 - 490
I like the Nikon p-series mounts with a 2-7x32 Vortex or Nikon set the scope forward enough that the tip of your nose just barely touches the charging handle right in the middle of the scopes eye relief range.
as you change positions from seated , standing , prone so that when you pick your head up turkey neck it forward and drop your cheek on the stock your nose tip is right up to the charging handle