As we all know, all barrels vibrate and heat upwhen we push a bullet down them at speeds close to or exceding 3000fps no matter how the barrel is made or whoever made it, bar none. Yes to the question do they work, at least on the rifles I have tried them on. Sims reccomends they be placed either near the end of the barrel(app 1")or app. 1" from the forearm, all my rifles have them at the forearm. My 7mm08 was the exception, itshot much better with it at the end of the barrel.

What I saw was the first shot it made no difference at all, which makes sense since they were "cold barrels", but as the barrels warmed up the groups did not "wander" at all, even on extremely warm days(you may have to try it at the end of the barrel or at the forearm for best results). Example my 308 NEF Survivor bull barrel, with 168g Federal Matchbthp always shot under 2" at 200yds, but as the barrel started to warm up on very warm days the groups started to widen, my last 5shot group(with outside temps in the mid 80's)wasslightly over 1"(at 200yds)with no cooling between shots, impressive to say the least.

All of us want our first shot to be the only one we need in a hunting situation, but it is nice to know if we "need" that second shot it will go to the same hole if we do our part and hold it there, and the Sims will help with that, and it is not an expensive tool. And shrinking our groups in halfis a good thing for bragging rights alone, and increases our confidence when we have to make the shot count, and no I don't work for Sims......lol