.065" is what I used for years for the longer factory length barrels. When I installed the Choate on "Maggie", I cut the barrel somewhat down to 17", she still likes the .065".
I finally got around to cutting the other Mini, "Sasha" down to 16.5" and she needs the full .100" bushing for sure.
Phineas, after shooting, does the "starburst" fouling pattern on the muzzle look even at all points ? I can send you the hand tools to re-crown after I get them back from Hylander. As others have said, it's hard to discern any slight defects in the crown, easier just to re-do it. I've not been impressed with the factory crowns I've seen.
I like my Tech sights and shooting with irons occasionally, but you should try a micro red dot. Better in low light, faster to engage one target or multiple ones, and when mounted forward away from your head, greatly improved peripheral vision.
Burris or Vortex make good, middle of the price range micro dots.
Bepe, I've never used A1680, I think it was A2015 you meant. That's all I've ever used in the x39.
Had meant to try some H4198 as you have had good results with it, but haven't done any more x39 loading the last 2 years.
When I started to load for the x39, Hornady bullets were readily available, were the proper diameter not undersize, and are known for accuracy.
I stocked up on the SST for my defense stash, and used the Hornady FMJ for range use. Their FMJ (now discountinued) was made with care, unlike other FMJ bullets, and I got great accuracy with them. Not as good as the SST, but still great.
This was with my wood stock gun and Nikon scout scope mounted on the Ultimak. For some reason I haven't been able to figure out, "Maggie" gets a good 150 fps. less with my SST handload than the other Mini. Other loads she shoots at normal velocity though. Weird.
I got good results with the Varmeggeddon bullet too. Both the Nosler and the SST shot the best with 28.6 grains of A2015. (Hornady shows a max of 28.5)
I find Hornady data to be more "normal" than most, not hot or too conservative.
I have to disagree with A1680 being known as the "go to" powder for the x39. I'm sure accuracy is as good as other powders but Hornady shows a full 2400 fps possible with H4198 and A2015, while A1680 tops out at 2200 fps.
Seems the slower burning H4198 and A2015 are optimal.
If your x39 loads are only 2000 to 2200 you are getting down to .30 Carbine power.
Handloading allows more options as well. These are some tracer rounds I loaded. I got the bullets from a supplier in Phoenix, he got tracer bullets pulled from AK ammo imported. I guess it was legal for him to import the bullets but not loaded tracer ammo.