So by the "base" I imagine that you mean the breech, the closed end of the barrel that's next to the lock.
So you want to have the breech checked to make sure that as mentioned above, the breech area is safe to shoot.
IF the bulge is filled by loose powder when the normal powder charge is present, then you likely can simply remember not to use less powder than that "normal" charge, and shoot the rifle. However, IF the bulge is slightly ahead of where the normal powder charge sits..., then you can load a "filler" of something like cornmeal or grits on top of the powder, between the bullet or the patched ball and the powder. This will keep the projectiles from losing contact with the rifling, and you should be able to shoot the rifle with accuracy. I would not do this, however if the bulge is more than 1 inch beyond where the powder sits when the normal powder load is in place.
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