Yes I do reload but haven't set up for 223 yet. And honestly iv only tried 3 types of factory ammo in my Howa. I'm thinking now of just getting it into a better stock and trigger and picking up dies and Components to see what I can get her to do.
Does your Howa not have the Howa Actuator Controlled Trigger system (HACT)? If it does, that is fairly easy to tune polish and lighten up. Easier than shelling out for a new trigger anyway. If you take your time and do it right, it will feel as good as any trigger you have felt.
Does your rifle have the Hogue overmolded stock without the aluminum block? If so, scrap it for a good laminated stock or a Bell and Carlson Medalist and then skim bed it to the action. Hogue overmolded stocks are not known for their accuracy enhancing characteristics...because they do not have any.
Does your rifle have the Nikko scope? If so, they are not great. Scrap it and get a better scope.
Have you tried higher quality ammo? If not try a box Federal match grade ammo or hand loads tuned to your rifle. Try a box with relatively light bullets, a box with mid-weight bullets and a box on the heavier end of the range. That will at least give you some idea what the rifle shoots well in terms of bullet weight. Twist alone often doesn't tell the full story - I have a 1:12 that shouldn't handle heavier .223 very well but it puts all of them on a penny at 100 yards.
Also, check the crown on your rifle. If it looks funky, have it recrowned with an 11 degree crown. This will often dramatically reduce group size on Howas.
Lastly, have you tried copper seasoning the bore? That is, not scrubbing all the copper out with copper solvent between trips to the range. Use a standard powder solvent but let the copper build up a little and see how the rifle responds to it. This will shrink the size of your groups with many bolt action rifles.
There is nothing at all wrong with a Howa 1500 action - the problem is usually with some of the other components bolted to it (flimsy Hogue stock and NIkko wandering zero scopes).