Welcome Jake,
I also have a 1:10 twist, but mine's 23" long. One thing I've learned in shooting a 1:10, is everything, including lands/groves configuration, barrel length, and twist, is going to make your barrel shoot different than the guy posting his load for a 1:12 twist, 24" factory barrel. While I'm not saying 3031 is a bad place to start, I see it's listed in the Hodgdon online load data, but I've never seen anyone post loads for the .204 in any online message board, and I thought I searched them all... I probably have not seen a few out there, but anyway... It sounds like it should work fine, but you're probably on your own anyway for loads that should be accurate, considering the configuration of your rifle.
Another thing I recommend you keep in mind when looking at load data for any cartridge that will cycle through an AR-15, is you'll need to load to magazine length. I find MOST pet loads posted on the Internet for the .204, were seated longer than the recommended 2.25" COAL needed to fit in an AR magazine. Loading yours shorter than the company or guy on the Internet posted online, is going to require you start your loads LOWER than theirs, if indeed you need to load shorter than they recommend. You'll just have to be the judge of how much lower. FYI, it's been found that the .204 Ruger's case dimensions are enough different than a .223 (longer distance from base to shoulder), that it does not cycle as easily as .223 through an AR-15. I've had good luck with mine, but some have had trouble. When I set my seating die, I measure about the first 10 rounds I load to ensure no cartridge is longer than 2.247". This is really all you can do if you want to load them as long as possible. I've had bullets with ballistic tips vary by up to .020 in length from base to tip, so you can't measure off the ogive or you may get some where the plastic tip is out of spec (long), and may not cycle through your AR correctly. I think some AR magazines will actually hold cartridges as long as 2.26", and you can modify the lips to cycle longer ammo too. Sometimes though, the problem with the .204 comes from the bullet tip hitting the top of the chamber as it's fed.
You might start
here to get some ideas on what's working best for people on this forum, although I have a hard time interpreting whether it would be safe to try some of the loads listed, considering I don't want to load mine to 2.31". Again, most loads people post on the Internet are for 1:12 bolt actions with 24"+ barrels.
I think what would be best to offer you at this point is that in my experience, ease of finding accuracy in my AR came from H4895, Varget, and Ramshot TAC. Others with bolt actions around here seem to get their best accuracy/velocity with faster powders like Alliant Reloader 10x, Ramshot X-Terminator, W748, H322, H335, and Benchmark. In my AR-15, I found that any powders faster than H4895 would not cycle the action. The round would fire, but I might get a jam, or the bolt would not come back far enough to grab the next round in the magazine. Some here with AR's shoot the faster powders with no problems at all. You'll have to test their loads in your rifle to find out. Just try to do it safely.
One thing nobody told me until I had already loaded hundreds of .204 rounds, was to use magnum primers like CCI 450 or the new Wolf "223" for ball powders, but standard small rifle primers for anything else. Stay away from Rem 6 1/2 and CCI 400 primers, as their cup thickness is too thin for higher pressure .204 loads, especially in an AR-15.
If I think of any more tips unique to loading .204 Ruger cartridges for the AR-15, I'll try and get them in here for ya. Good luck!
Gary