Are any of the bullets pulling out under recoil? shoot 5 rounds and check the 6th to see if it has pulled out past the crimp groove. I seat and crimp in 2 steps. I would crimp until the case mouth is pressed well into the cannelure if they showed sighns of pulling, or use a Redding Profile Crimp Die.
If the above does not apply.... You are not using enough powder. H110 must not be reduced below 3% of MAX! Hogdon says this for a reason. Hornady lists 24.8g max for their single action. Considering your double action should have a larger cylinder gap, and, the fact your using a light charge, it sounds like you are not getting enough pressure from that charge to seal the chamber.
Or basically you are not getting enough pressure to expand the case, which is nothing but a gasket, and that's why your getting blow by.
Try increasing powder charges, {in accordance with safe reloading practices}, .2g's at a time until you reach the proper charge for your combination, it should solve that problem. Stop increasing the powder charge when you see that you are not getting the same average velocity increase per .2g of powder increase, {that is the "efficiency window" any more and you just increase pressure!}, or when you see that accuracy is starting to open up. I like AA#9, it is more forgiving.
Magnum primers are a must. Are the cylinders oversize? Any more than a few thousandths over what a resized case is and they could be considered on the "loose" side.
Good luck and be safe.