TOW drum & nipple tool

[DFHicks]

Eight years ago I built a caplock rifle using the drum and nipple system.  I had trouble getting the nipple to line up correctly with the hammer.  On the second drum I "fixed" the problem with a thin shim between the barrel and drum.  I didn't realize this is not a good idea.  So sure enough the rifle has started to leak gas at the joint when fired.  So I need to install a new drum.  The tool offered by TOW for this seemed like it would help so I ordered one. It is well made and has the advantage of once you screw the drum in tight, it isn't removed.  Before I used the approach of marking the spot and taking the drum out and drilled the nipple hole in the drill press.

Now here is what's probably a dumb question _ despite the advantages of this tool isn't it lined up "by eye" just like the other method?  Maybe I am missing something as I am not the sharpest knife in the drawer.  Has anyone used this tool?  Other insights into this procedure?   
Thanks,
DF

[galamb]

I do use this and hope I can explain how without getting you overly confused (sorry, have never thought to snap a pic).

First off I have a collection of "small jigs" made out of 1/4" dowels. They are representative of the length of "exposed" nipple (once screwed into the drum) for the few different nipples I have used (rifle length, pistol length and very short "snake eye" nipples) - flat on one end, rounded to the shape of the drum on the other.

I screw the drum into the barrel (or breech in my case, only build with a Hawken style flint patent if using a drum), to it's final "tightened in" location.

I then place the little dowel between the hammer cup and the drum and get all the geometry "correct".

I then take a fine tip permanent marker and draw the "circle" on the un-cut drum using the dowel as the guide.

I remove the dowel and the lock, put an X through the circle that was drawn (making sure the X crosses exactly in the center.

Then with the help of a flashlight, I center the guide on the marked circle. With the "bushing" removed from the drilling guide you can clearly see your marked circle/X and get things lined up perfectly.

Then just drop in the drilling bushing and get out the hand drill.

Viola' - a perfectly lined up hole ready for the tap..

[DFHicks]

Graham,
Thanks for the reply.  This really helps.  Just to be clear you round the bottom of the dowel nipple stand-in to the curvature of the drum (1/2"is what I have) _ correct?  I would never have thought of the flashlight.  Can't wait to try this.
Regards,
DF

[galamb]

Yes, correct, I put a (crescent) shape into the bottom of my jig/dowel so that it follows the curve of the drum.

This results in the (outside) circumference of the dowel in full contact with the drum when I draw around it with the marker.

[DFHicks]

Graham,
Thanks again; guess I am ready to take on this repair.  As everyone on this forum knows it would have been better to have done this while the stock blank was still in the square.
It makes me nervous working with a slim stock minus the barrel out even though I have a wooden "barrel" tied in place.  Live and learn, I guess.
Regards,
DF