https://www.armorally.com/shop/vg6-cage-muzzle-device-combo/
I have this on order on @98Z5Vs advice. I did not see this sale when I ordered mine. It would have saved me about $30. I have bought from this place before without any problems.
If you want match ammo, watch for Federal Gold Medal Match at Palmetto State Armory to go on sale. It runs for $16.99 a box periodically. It's just not on sale right now.
Thank you sirs. I believe I was looking at those exact two scopes earlier today. It's good to know that I was on the right track. I will get to that mount shortly.
Others will reply with more specifics, but there is little difference in accuracy or velocity between a 16" and 20" barrel out to 500 yards. There is a thread somewhere on the forum with that specific information.
It is dependent on having the proper length receiver extension with the proper length buffer. As @jtallen83 said, a RE that is too long with a standard spring will still be too long with a Tubbs.