I really like 5744, but I bet it isnt all being burnt.I also
...also love my .45 Colt. I use Unique for lighter bullets and 296 for the big ones......but it is such a difference in caliber to .308...I just dont know much about Lil Gun. I am betting that it is slower than 1680...but what I dont understand is that I have seen a lot of Whisper data for 296. So, I think you are barking up the right tree. Although...the 296 data for 45 is for BIG bullets 260 gr.and upwards...so my best guess is that the Lil Gun would work also if used with the proper weight bullets. Why dont you try whatever data you have for Lil Gun in your Whisper in as close to a comparable bullet weight with a starting load and work up .5 grs at a time. As you might know...this could be dangerous. So with however grains of salt..or powder as the case might me. But the best thing in my opinion is to call the manufacturer of the powder...they might be able to suggest a starting load.
Now on the other hand.....those little 90 XTP's are exactly what i am loading....the first shot I tried at 25 yds was a little low and left, but my scope needed focusing, I had just put it on. I adjusted it so it was clear at 25 yds and took a second shot and thought it went through the same hole so I walked up to get a closer look. The second shot had perfectly removed the center dot I had drawn with my marker. They were loaded pretty hot with 20 grs. of 1680. Next I tried some 200 gr Billy Bullets loaded with 12.6 of 1680, and of course they were shooting a little low. Tommorrow, if the weather cooperates..I will compare both at 100 yds along with some 190 gr Honady boatails that I havent tried yet,....I am betting the bigger bullets will be more effective at longer range..maybe even out to 200 or more.