I contemplated building a 20 Vartarg for sometime, but could not get past the proprietary dies etc. I ended up building a .221 FB and have never looked back. Lower cost, less hassle, no .20 cal. cleaning stuff to buy, more load data, plenty of .22 cal bullets.
PS, if your using a 700 action, make sure you start with a Fireball donor, and not a .223 donor.
What is the difference between a Fireball donor and a 223 donor?
