Look up how industry carry out dissolution experiments. If you have a disso instrument it would be ideal. If not, disso experiments are carried out by stirring (gently) a tablet or capsule in your medium, in your case stomach acid. Then you take samples at set times over 24 hours and test the amount of drug in the medium, normally by HPLC. In your case doing solubility measurements by mass wouldn't work too well due to the KCl, but if you know how much is dissolved then you could subtract it. HPLC would be better. You'll get a dissolution profile over time which should eventually level out if the medium becomes saturated or if all the drug is dissolved. So you can compare the profiles between tablets and capsules to see which is faster. Normally it correlates to have quickly the tablet disintegrates, which is another test done in industry.