I've just shot the final load on my final ladder test with Reloader 10x. I can't say I'm impressed, although I have had good results with Alliant powders in the past. The 10x grouped fairly well with 40 grain sierra and hornady bullets, 45 grain hornady hornets and ok with 52 grain sierra MKs, but nothing spectacular, yielding about 1/2 MOA at 200 yards. Chrony data revealed about what I had come to expect, again, nothing spectacular, but ok data. I'd say if you're looking to make a big improvement in your groups, the 10x will not do that unless you've been using something that tends to yield significant variations in the .223, like Varget did for me and some other folks I know.
Actually, on looking back over old load data, I had better results in .223 rem with Reloader 15 in 52 and 55 grain bullet loads, though the best results I can attribute to a powder have come from using Vihtuvuori N133 although they do not recommend that powder for the 22-250, but instead N140.
Several of us at our club found that the Varget we were using (from 3 different lots) tended to have density problems. A grain of powder (the piece of powder not the weight) might vary as much as 40% which made measuring powder charges by weight hard to do and by volume downright impossible. We had all had the same problem and found out at a business meeting. Since then (about 2 years ago) It seems that the Varget people down under, have addressed the problem. We have one shooter here who likes to pursue these little quests. Personally, I just moved on to using Vihtuvuori.
I've also had some pretty good results using Winchester 748 in the .223, but I still have not found a powder to beat the N133 for consistency.
"If the enemy is in range, so are you." - Infantry Journal