Hello,
I shot a .41 Mag 14" T/C factory barrel for years. I found that other than powder, primers and cases in good condition, the following were worth the attention:
1) Ensure that case lengths are all identical - trim them to the same length with each firing.
2) If you're using a carbide sizer, try only sizing the first .400" of an inch of the case - leave the rest of the case unsized, as long as it will still fit into your chamber. Make sure all the cases are sized in exactly the same manner.
3) I had my best luck with Sierra 170's and Sierra 210's in that order
4) Experiment with seating depths - my best accuracy was with the bullets seated pretty far out. I still tried to keep enough bullet in the case so they wouldn't fall out.
5) Uniform your primer pockets - I'm lazy and got the Sinclair drill attachment for my primer pocket uniformers - what a wonderful time (and wrist) saver!
6) Use a scope of sufficient power to see your target correctly at 100 yards, it does make a big difference.
7) Index your cases. Make a small mark with a file on the rim and place the mark in the same place for all reloading operations. Place the bullets in the chamber with their marks all pointing to the same spot (i.e., point all the marks at the center of the extractor). Indexing cases has proved to be more effective for me than any other reloading tip. Do it religously and it will make you a happy camper!
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Use Fastex and coat your bullets - what an improvement!
9) You can always have the barrel rebored to a .41 GNR #2 by Gary Reeder Custom Guns. I now own a 13" SS Reeder .41 GNR #2 (.445 SuperMag case necked down to .41 caliber) with a muzzle brake. . .believe me, YOU WANT ONE! Accurate, flexible and hydrostatic shock you won't believe with .41 caliber 170's flying out at over 2,600 fps - what a rush!
I hope this information is of help to you. Please don't hesitate to contact me with questions/comments.
Javelina