Yes they work, especially for getting bulk ammo to shoot tighter groups. Someone several years ago did a test on RFC and posted photos of the targets using Fed. 550 bulk from WM and the groups shrunk by at least 30%. Some rimfire benchrest shooters use them also. The position has to be tuned for your particular ammo to get the smallest groups but just putting them near the end of the stock or handguard can get improvement. The one time I tuned one on a Rem 597 the best spot was about 6 inches from the end of the barrel using CCI MiniMags. When I rebarreled the 597 with a Volquartsen carbon fiber tensioned barrel and a Jard match trigger its accuracy got down to .5 MOA without the barrel de-resonator using CCI-SV so I did not bother to put it back on. They also work on centerfire rifles. Sometime next year I plan on putting them on a couple of my other rifles and tuning them to see what they do on centerfire (I have one each of the sporter and bull barrel versions).Thinking about putting the bull version on my .308 LR match rifle to see what it can do at 1000 yards.