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.41 caliber pistol bullets are generally .410 (jacketed or cast) or .411(cast). They probably wouldn't fit your barrel very well, and I wouldn't expect a lot accuracy-wise. However, barrels are individuals, and some shoot undersize bullets reasonably well.
With cast-lead bullets, powder gases escaping around the loose-fitting outer circumference of the bullet might give you a good case of leading in your bore.
The expander plug in your sizer die is probably ground to expand your case necks to about .413 or so. If you choose to experiment with .41 pistol bullets, you may have to remove the expander plug from the stem in your sizer die to get enough neck tension to hold the bullets in place.
Cheers,
BigIron