I was hoping for actual short barrel lengths lol... 16 inch, or in your case 16.5 is no problem at all. Personally I use the same powder, varget, in my 16 inch 308 and 26 inch 308.I will say that the ar10 is a different animal and DOES have different needs.
No complaints, just a bit lower velocity from the shorter tube. They say the best powder tends to be the best regardless of barrel length, though semi autos can be different. Accuracy and precision are great with both, though the shorter barrel seems to be notably more blasty... as expected.
I am using a Desert tech rifle, with a 16 inch 22 inch and a 26 inch barrel for my comparison. Everything is the same for the comparison except the barrel.The shorter barrel generally runs a little under 2500 fps, and the longer one is closer to 2700 fps. Same loading for simplicity sake. 178 amax and varget at standard coal. Load is not hot and brass life is excellent. Both barrels are better than .5 moa with me shooting this load when I have been practicing as I should, so clearly I am the limiting factor here. They shoot just as well out to about 700 yards, the longest shot I have easy access to. I can also add a 16.5 inch GSR in 308, a UGSW 308 18 inch barrel, a GAP Hospitaller in 308 with a 22 inch tube. They get pretty much the same loading with the SAME powder regardless of barrel length. Minor tweaks between all of them in COAL etc, but they DO shoot as well as I ask them to with the same powder. I am not a bench rest shooter, rather a precision/practical oriented type of guy. Maybe that extra .01 can be shaved off my group, but to be honest I like shooting more than loading, and once I find a loading that works how I need I shoot it.
I frequently shoot my GSR, as it is my hunting rifle, so hopefully I can help. It likes a wide range of bullets and powders. Mine is not picky at all. I load to standard length with a charge of Varget. CFE223 is excellent as well and tends to offer a bit more speed, but I am much better stocked on varget and do not want to add another powder. 43g of varget and a 175 SMK or 178 amax runs just about 2475 from my rifle with Fed brass. Velocity is obtained with a Oehler 35p that is known to be reliable. Accuracy is easily sub MOA with minimal load development and no fancy loading practices. I have taken deer out to 350 yards with this rifle/loading, and steel torso targets are not problem out to my longest shot here at about 700 yards.
Start under any loading you want to explore and figure out for your rifle of course, as yours most assuredly is not the same as mine.
Not sure if you are into it, but my GSR shoots VERY well with cast bullets, 160s @1850fps. Bullet is a ranch dog flat nose GC. Probably one of the best and easiest cast bullet rifles I have gotten to play with.
All that said, I think it may be possible some powders can be better suited for short barrels, but without much experimentation I am not sure how noticeable it is. In the 308 application I am after precision with ENOUGH velocity, not chasing rockets, so I have typically not found a reason to switch powders based on barrel length. I would not be opposed to trying other powders based on barrel length, but I have never seen the need. The only caveat there would be with actual SBR lengths or semi auto rifles. As to blast difference between powders in a rifle, suppressor and/or ear plugs make that a moot point.
SOOO, for all practical purposes I think you would be quite happy with a charge of varget whether your barrel is 16 inches or 26 inches!