Here are my latest 20 Vartarg results with the 55gn Bergers, adding in IMR3031 and Benchmark. These loads were worked up with Lapua 221 Fireball brass, CCI400, in my Hart 1:9 26 inch barrel, chambered with my custom reamer that has some key alterations made to the Todd Kindler original design.
I purged the reckless, brass destroying max charges listed in the previous version.
Top loads listed here are still very hot, or in the case of 3031, completely full with bullet deforming levels of crunch. Please approach the top loads with extreme caution. All these top loads showed me a little heavier bolt lift. Many of my primer pockets are noticeably looser now, so these top loads are no joke. My Borden, with a tight fit firing pin and strong extraction cam, can handle more pressure than any gun I've ever owned without showing signs.
Let me qualify my comments below on accuracy as it pertains to the little 20 Vartarg. I define exceptional accuracy as regularly falling below 1" at 300+ yards, even in windy conditions. Average accuracy would be ~1.5" at that distance. All these loads shoot tiny at 100 yards - less than 0.25MOA, and all of them have shot sub-1inch at 300 yards at some point, but some of the loads just seemed more telepathic, if that makes any sense. I knew as I broke the trigger where it would go and that gives me huge confidence when I'm shooting it. I can certainly see why Harold (I think it was) campaigned a 20 Vartarg in SR BR and did well. This rifle has been phenomenally consistent and I am a huge fan!
I think the two 4198 powders are still giving the best accuracy and are what I would recommend. IMR4198 is stable and accurate, and while the long kernels don't meter well from a powder throw, they work great in my Chargemaster Lite (each charge is trued on an FX120i, and they never vary more than 0.06gns). At the charge weights you can achieve in the 20 Vartarg, IMR-4198 fills the case nicely without any compression. Some tune adjustment is needed across bigger weather changes to keep the fine edge. H4198 is good too, but due to the smaller kernels it leaves more room in the case which I consider a little sub-optimal. I don't really need to extoll its other virtues here; it's a great powder and everyone knows it. H4198 requires less tuning than the other powders except maybe Benchmark.
AA2200 is a nightmare; it is incredibly temperature sensitive! 19.5gns listed here will be ok when the gun is cold and clean, and it's only 70 degrees F outside. If the gun is hot, dirty, or the temperature is above 80, that load will trash the brass in 1 shot. In 30 degree F weather, like yesterday, it slows down to only 3140fps and shows no pressure at all!
I really can't recommend anyone use AA2200 for accuracy work. Even dialed down to 18gns, it swings all over the place.
IMR-3031 works fine, but the large kernels fill the case and it gets crunchy quick. Nothing much to report; it works fine and produces normal accuracy. Perfectly suitable if that's what you've got in the cabinet to load with!
Benchmark is a great powder for the 20 Vartarg with certain reservations. It requires a long drop tube, slow pour, and some tapping on the case to get it all in. Great accuracy is achieved though, right there with the 4198 powders and TONS of speed with a noticeably sharper "CRACK!" when fired. Like a whip. Reason I don't recommend it more than the 4198s? Well it's a lot of work to get the powder all in with an 8" drop tube and seat the bullets consistently without damaging them. If you don't pour slowly enough, you'll lift your funnel off and dump some kernels on the bench. If you pour slowly enough, but don't quite get it to settle right, then you'll have a bear of a time balancing the bullet on the stack of powder as you run it into the seater. I end up seating it in 3 stages to get to final depth and sometimes, despite all the work, it deforms the bullet anyway. It doesn't shoot smaller than the 4198s, so the extra speed doesn't seem to be worth much except bragging rights.
Ramshot X-Terminator is a ball powder that seems to be much more stable than AA2200. I'd recommend it if you like to just "throw and go" for varmints. A lot of powder fits in there, and it's a slow powder. Average accuracy.
But, slow as I may be, I did "fix" the issue. Oh, it did this to out-of-the-box LAPUA brass. 
