probably 1:7 or 1:8
i have a 1:9 twist which can stabilize the 69 gr SMK but not the 77 gr SMK which have a slightly higher BC
mine does perfectly fine out to 600y though, 77 gr SMK might give slightly better results
sorry i know NOTHING about these kits and if they are legal or not
what i did was bought a stnadard A2 lower and a Varminter upper both from Bushmaster, put a Leupold VX-I scope on it with some leupold rings and a Harris bi-pod
i strongly reccomend the Bushmaster Varminter barrel/upper reciever
for $1410 i have an excellent rifle which always consistantly gives me 1/4" groups @ 100y, often less with Federal Gold Medal Match 69 gr
and my Varminter isnt the only one that gives consistnat accuracy
i followed my friend when i shot his Varminter and many other people i know have them now, they are all consistant 1/4 - 1/2 moa rifles with the factory ammo
i hadnt fired one yet that didnt shoot well below 1/2 moa
