Here's how I've modified my Lee 45-70 factory crimp die, and it seems to work well.
First you have to get the die apart. I had to try several methods; perhaps my die was really tight. One of the methods succeeded, but I've forgotten what it was. Sorry.
To modify the die, I dug out my little Sherline lathe that I got on eBay a couple of years ago; it's pretty ancient.
I put the die body in the 3-jaw chuck, and cut off the base so the length of the die body is 1.660 inches.
Then I put the collet in the 3-jaw chuck, and cut it off so that when the collet is in the die body, the collet extends 0.50 inches below the die body. (This measurement is made with the collet pushed finger tight into the body.)
As many have noted on this site and on the calguns thread. the crimp applied by the Lee die is too wide. So I reversed the die in the chuck, and turned off "some" of the width of the crimping ridge (ring?) so that it would produce a narrower crimp. I cannot measure how much I turned off. I did not alter the internal diameter of the ridge of the collet, so the diameter of the crimp it applies remained the same.
Using the modified crimp die with 450B cases, the center of the crimp will be located about 0.20 inches from the case mouth.
At the point where the crimp is applied, the diameter of an empty case is reduced, from about 0.483 to 0.468 inches, so the crimp is about 0.0075 inches deep. With a jacketed bullet present, it really makes the bullet into a wasp-waisted shape.
At 0.20" from the case mouth, the crimp to too far from the mouth to be useful with many bullets, and in particular with the 185-grain SWC bullets with which I've been playing. I use a common method for solving such die problems: the case is put into the shell holder of the press, and a washer of suitable thickness is placed over the case so it rests on the shell holder. With the 185s, I use a washer that is 0.130 inches thick. This moves the crimp that much closer to the case mouth.
Different thicknesses of washers can be used to adjust the crimp location precisely where it's needed, for example into a cannelure.
Below is an image showing a 185-grain fully encapsulated semi wad cutter (Hornady #45137) .451, diameter, crimped into the case. The Lee crimp was applied after using the Hornady taper crimp to take the mouth diameter to 0.476 inches. The Lee-crimped case is flanked on the left by a Hornady 250-grain FTX factory load, and on the right by one of my 250-grain FTX handloads. The crimp should be obvious. There appears to be a slight flare at the mouth, but in fact the mouth measures 0.476, just as it did before the crimp was applied. I applied the Lee crimp after the taper crimp because I worried about the taper crimp possibly loosening the Lee crimp.
In Chapter 7 of the 185-grain SWC saga, I'll try to describe the results of using the crimp.
Please post if there is something unclear in the above, and I will try to clarify.
--Bob