I fully understand shooting gophers, so I won't go into why I don't like shooting them anymore. It's fun and in many circumstances, they overpopulate and become a destructive nuisance.
My reply, is more about the accuracy increases with the "Waltz" die.
It's not a new concept by any means. There used to be several different makers of a similar die.
I tried a similar type for ammo being used in two different match grade, small action Martini rifles, chambering the 22 LR.
One of these rifles had an actual minor bore diameter of .218 and the other .220.
At fifty yards, shooting from bags on the bench, dime sized groups with cci standard velocity ammunition were consistent with both rifles.
I tried other types, but even though there was improvement, not enough to justify the extra expense at that time in my life.
A good friend, Sgt Walter Rogers, PPCLI. suggested a similar die and he just happened to have one.
On the rifle with the smaller minor diameter (.218) there wasn't any noticeable or measurable difference in group diameters over ten rounds.
However, the rifle with the .220 minor diameter bore showed significant improvement of group size.
I sold the die with that rifle, to help pay for a nasty divorce, one of the regrets.
Another friend/mentor, Al Forslund, had a different type of "die" which was used to uniform rim thicknesses on the 22 rimfire ammunition he bought to shoot through his Lilja, bolt action repeater, with a Lothar Walther barrel, with a .218 minor diameter.
He took off the barrel and set it back about an inch, then recut the chamber so the bolt would just close snugly on the smallest rim thickness he could measure on several hundred 22rf cartridges.
He made up a die for his RCBS press so that he could compress the rims of all the cartridges he was going to shoot through that rifle so they were all of uniform thickness and the bolt would close consistently on each case.
He also used a match reamer for the chamber, which I still have.
That rifle shot any type of ammo he put through it incredibly well.
Different brands would shoot to different points of impact by .250 or less, but the groups were all around .350 with the same brand at the time.
If that Waltz die is actually improving the accuracy of your rifle, I'm willing to bet that it's expanding the bullet diameter a thou or two when it's forming the flat top or punching the hollow point.