Yondering, any more on this one?
Actually was just loading some more ammo for it last night. I should take some pics of accuracy targets but haven't done that yet (I really prefer shooting longer distance at steel and other targets once I figure out a load); however, I found it shoots the best (and IMO very well!) with the 40gr V-max over 31gr of Lever for 3917 fps avg at the muzzle. I ran a seating depth test with varied powder charges at each depth, and found that 2.255" OAL shot really well at 100 even with a full 1.3gr variation in powder charge, so I'm loading in the middle of that range and calling it good. I did confirm through a lot of testing that Lever is THE powder for the 40gr V-Max in this rifle; nothing else ran as fast or shot as well.
The 32gr V-Max shot reasonably well with X-Terminator, but struggled to pass 4100 fps without really pushing the brass, and at that speed it gives up a lot to the 40gr load so I didn't bother with it further.
The 24gr NTX is an interesting one I've been experimenting with. There is factory data for it in the 20 Tac, like the Sierra manual, but if you really look at the numbers and powder choices is severely underloaded and hampered by powders that are too slow and fill the case before reaching full potential. Since I've got a pretty full selection of Ramshot and Accurate powders I did the wildcatter thing and started messing with those, stepping faster in burn rate until things fell into place with AA2200. The max load with that one put that 24gr NTX a bit over 4,800 fps (no joke) but I found a decent accuracy load in the low 4,700 fps range. That one doesn't shoot as well as the 40gr V-Max, and loses steam fast, but it's a neat little bullet to fire at warp speed. It also has almost no perceptible recoil other than the bolt carrier movement; it feels like less than my 22 Hornet.
An interesting side note though is that even though it's doing almost 1,000 fps faster than the 40gr loads, it doesn't penetrate steel plate any better. I think that powdered copper core is just so frangible that it comes apart too fast. I did find one example when I had my target mounted to a cardboard box that it split the side of the box and fully fragmented within ~3 inches of entry on just the cardboard.
Anyway, it's a really fun round and a blast to shoot in the AR. It's very low recoil compared to the 5.56 which is already pretty mild, and is an absolute laser beam within ~300 yards. Also, as usual I'm really happy with this Black Hole barrel. I've got another build to post up when I get time; this one is a 19" octagon barrel in 243 LBC, set up as a mid-light weight walking rifle in the AR15 platform. That one includes a thumb surgery story too since I did a very dumb thing and found out what the bone looks like under my thumbnail.
