I'd start at 25 yrds. You can take the breach plug out and look through the bore at a target, then the scope to see if it's "close". Adjust as necessary. Then move out to 50 and dial it in. Once dialed in at 50, you should only need to raise the POI at 100yrd+.
What powder, bullet do you have?
Do you have a bullet starter? Definitely a helpful tool.