Also keep in mind JP Enterprises makes a 5/8-28 (JPRE-428) and a 5/8-24 (JPRE-424) threaded Recoil Eliminator. It may be that you received the wrong one.
Printable View
I've played with a lot of different brakes and my current favorites are the Terminator series out of New Zealand. I run a T4 on my 338/408 Improved rifle and a T5 on my 338/408 Improved pistol. This is an 18# gun shooting a 300gr bullet over 143gr of H50 BMG. The gun moves straight back about 2".
https://youtu.be/pQ6PEAWF5Zk?t=40s
Nothing I've played with is even close to be as effective as these brakes.
if youre thinking about getting the tank and hae a savage barrel threaded 5/8 x24