What type tuner are you using and how well does it work?
One, then two 7/8" id Amazon steel shaft collars roughly 0.4"-.5" from the end of the non-threaded barrel. I use a depth micrometer to measure the distance from the muzzle and have been moving the collars in about 0.010" increments to see the effect. The weight of the two collars is about 6 ounces, similar to a proper aftermarket threaded barrel tuner. The rifle shoots pretty well without any tuning, but I can make it shoot terribly WITH the collars in certain positions. The shots in the video above were from the o.510-0.535" range, but the accuracy went south before I could confirm repeatability. So I removed the weights and confirmed the barrel accuracy was nil with or without the weights, so packed up and went home.
On Tuesday, with one collar and only a caliper to crudely measure position, the most interesting result I got was good results using the Norma Match ammo that I have always used in my Kadet at 50 yard bullseye matches. That ammo simply would not shoot well in the MTR, as in 2-3" at 100 yards, compared to 1" with the SK Rifle Match. I put the single collar on and started getting around 1" with the Norma Match. Quite surprising. And seemed repeatable, but I didn't do any fine tuning. When I removed the shaft collar, the Norma group went back to 2". So, in theory at least, it may be possible to use a weight to make otherwise good ammo a better match for a particular rifle, with the resulting group size variation proportional to the SD of the ammo in use.
As Europe pointed out, consistency is what matters. Five and ten shot groups tell the real story, three shots are good enough maybe for experimentation to show me roughly when the collars were in a favorable position...or when the barrel is getting fouled again.
I'll make a video on the DIY tuner after I am convinced the effort is really beneficial. With the ammo shortage, I'm not in the mood to blow through another 200 rounds for a 1/2" improvement on one type ammo that may change slightly in the next lot.
Joe