Here is IMR's formula from their website on how to do it. http://www.imrpowder.com/PDF/Trail-Boss-data.pdf
I recently loaded some .223 with TrailBoss using this method. It came out as 6.7 grains of Trailboss which was 75% of max volume, Bullet is a 52 gr. Hornady BTHP match, coal is 2.248. I have not fired them yet, but all the pistol cartridges I've loaded with TB using this method were safe and pleasant to shoot. My .223 rifle is a T/C Contender with an MGM barrel, so it is fairly stout and I have no reservations about shooting them. Contact IMR by e-mail if your are still unsure.