The SS109 bullet is about the same length as the 68/69 grain bullets. I usually start with 68/69 grain load data for SS109 bullets. Their lighter weight does allow them to be pushed a bit faster than the heavier lead core bullets, which can allow the use of SLIGHTLY more powder but I'm not sure it's worth pushing it. Accurate Powder has M855 load data for A2230 for both 223 Remington SAAMI chambers and AR15 chambers.
The load data for the Speer 62 FMJ lead core bullet works too. Some of the Lyman load data is a bit dated. The Hornady load guide seems to be one of the most updated for popular calibers, if you get the latest version.