Several of us started shooting JLK 90 VLDs out of our AR service rifles in NRA XC HP in 2001. We all used 6.5tw bbls - mine were PacNor 3-groove, while two of my buddies used Kriegers. My initial loads were with N540, which gave just over 2700fps, but were right on the edge - bump the charge .2gr, and groups went wild. Switched to N550, and had much better luck; not so much with velocity, but with a powder that wasn't so erratic at the top end. One of the guys brought a bunch of these JLKs back from Perry in '03, and we all had no end of problems getting them to shoot accurately. I wound up abandoning both 6.5tw bbls & the 90s.
Fast forward several years to the availability of Berger's 90s - both the VLD & LRBT. I bought a few boxes of both, largely out of curiosity. Tried them in a PacNor 4-groove 1:7.5tw on a M70 action, and found that they shot pretty well, even some of the problematic JLK 90s from years previous. I read all of Laurie's posts on LRTargetShooting, and finally ordered a 30" Bartlein 5R in 7.2tw, and used it on my Eliseo R5, which has a Pierce TG action that I'd ordered with a spare bolt with .378" boltface. It shoots the Bergers & JLKs very well, even out to 1000yds. I don't find the VLDs to be all that difficult to tune. In fact, I've shot the Bergers from .020" jump to .020" jam, and had excellent results. Too bad Berger didn't sell enough of the 90 LRBTs to keep them in their line-up - they're even easier to get to shoot.
Looking back on the 'bad' JLK 90s - I recently read about bullets 'stripping' their cores in very fast-twist bbls in Harold Vaughn's "Rifle Accuracy Facts". Sounds to me like a very plausible explanation for the accuracy problems we had with those bullets, especially since they shoot considerably better in that PacNor 7.5tw bbl than they did in my 6.5's. BTW - one of my 6.5tw AR bbls blew up almost every type of bullet that I tried in it - JLK 80VLDs, Nosler & Sierra 69s, etc. The maker replaced it with a 7.7tw bbl at no charge, but that experience further soured me on the 90s, since at that point in time, I still believed the 6.5tw was a necessity to get the 90s stabilized.
Now that I know better, I'm having a lot of fun shooting the 90s again - even went out to 1400yds with Berger 90 VLDs out of a 223 AI bolt rifle with a 26" Krieger 1:7tw bbl. Litz's PMS ballistic program predicts that they go sub-sonic at 1267yds when launched at a MV of 2820fps, but even so, they remained stable, as my hits on the 1300 & 1400yd targets were still nice round impacts.