Shrewd Machine Varmint brake.
I searched for a side port brake without top vents that could be turned down to .718" barrel diameter.
Finally checked out the Shrewd Varmint brake. It is a drilled hole symmetrical side port brake that looked like it could be turned down, so I ordered one from Brownell's with a 9/16" x 24 tpi thread. After turning it to barrel diameter, it still had plenty of wall strength after being bored out to .328" for a .300 Win Mag.
I was worried that it might not reduce recoil very well, but after about 50 rds of 200gr Accubond handloads and Nosler Custom ammo, my son-in-law reports that recoil reduction is excellent, and noise level for the shooter is unexpectedly low.
Maybe this post will help someone else dealing with these issues.
Good hunting, Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member
A big fast bullet will beat a little fast bullet every time