A very good friend designed the BOSS system. We tuned Browinging BARs in 270,30/06, and 7 mag to shoot sub-half-inch groups, often in the 3/8" area. We stuck to a particular brand and weight of ammo. A Bolts in the same calibers shot slightly smaller groups, tuned easier/quicker.
I have not tried the approach of adjusting the tuner for a particular load I wanted to shoot, but instead worked up the load with the tuner screwed all the way to the rear, then started adjusting the tuner. The result of this method took a 1/4" groups, down into the zero's and 1's.
This method was repeated with the Mike Ezel tuner, RASS tuner/brake, and Harrell's tuner brake.
It is to be noted that after initial load development, within 1 revolution of the tuner, there may be 3-5 settings that will shoot a single bug hole, the trick is to find the setting that has a spread of 4 numbers or more that shoot that bug hole. This whole procedure happens quickly, not some long drawn-out affair. The load is then verified at 300 yards verified where sub 5/8" groups are plentiful and often 1/4"-3/8" groups are real world.
Winning in the Wind, Keith Glascock, is one heck of an F class shooter, national standing. His videos on barrel cleaning are the best I have ever seen.
With Keith's references to tuners, remember, he shoots the same 284 win or variant, the same barrel maker, same reamer used on all barrels. So, he has a constant in variables where he can tune barrels based on a long history of what works.
So, for hunters trying to improve their accuracy way beyond 1/2" groups, I feel that a tuner will help them tremendously. A guy has to have the patience to develop his load, then tune, and this is not for everyone.
Other than use working with the Brownings with factory ammo, I have no experience in using a tuner with choosing any ole load and then making the tuner take the load down in group size. This same would apply today with a PRS shooter or hunter that uses factory ammo to hunt with, trying to achieve the best groups he can get. When tuning the Browning BARs, the most we ever used on finding a "node" was around 40 rounds or less. A-bolts with the BOSS system took less tuning on the tuner, and I attribute that to the Gas block and three-piece stock on the BAR.
For a guy on a budget, the Harrells tuner/brake at $95 works like a champ.
A friend told me that a can company was making tuners to be used with their cans.
The OP was trying to find a way to duplicate the groups that his rifle shot with the Magneto Speed attached. A simple solution may be to weigh the magneto speed, then duplicate that exact weight with the stick-on wheel weights that they balance tires with. The position of the wheel weights may prove to be critical, and the whole affair may prove to be a waste of time due to positioning.