It seems really hit or miss. In a lot of ways. There was a tale on one site that a person rechambered, not rebarelled, a 6.5 mm arisaka for 30/06 and the rifle didn't blow up from squeezing a 7.62mm bullet down a 6.5mm bore. If that tale is true then it appears the adapter won't blow up your rifle if you plan to shoot a .311 projectile down a .309.bore. I didn't find any confirmed cases of damage of any sort. Take all the qbove with a grain of salt as its unconfirmed.
As for accuracy I suspect these adapters are going to provide average accurqcy with average ammunition and average chamber tolerances. If any one of the variables is out more than the average then there won't be accuracy to speak of.
I'm ordering the adapter mid may, hopefully will have found a suitable test rifle about the same time and can begin experimenting in earnest. My test rifle will be the cheapest used rifle in .30 cal I can find. I won't care if I tear up the throat and destroy the native chamber accurqcy.
I figure for the $30 or so and a cheaper rifle to experiment with it's worth trying out.
