I bought a 416 caliber RCBS "M"-Exander die for my 416 Rigby. I ordered this die because I wasn't able to seat the Northfork bullet in my 416 Rigby (using Redding dies) because the grooved bullet shank was getting stuck in the case mouth and pushing back the Rigby case shoulder. I tried chamfering the case mouth at 20 degrees, rotating the bullet during seating, lubricating the case mouth, getting a slightly larger expander plug from Redding (anything I could think of) with no luck. Mike at Northfork recommended the "M"-die, which slightly bells the case mouth with a tappered expander plug (this type of die is used for cast lead bullets).

My question is: has anyone used one of these and what is the best way to set one up?

I use them in a couple of different calibers, and in my opinion they are pretty much foolproof to set up. The expander is stepped, and provides a positive stop as the case mouth goes over the expander. The top of the case will bump up against the step in the top of the expander. You cannot go too far as that step stops the upward movement. Sounds harder than it actually is. You should have no problems. Examine the expander and you will clearly see the different parts of it. No worries, mate.

When loading cast bullets, which the lube grooves make similar to the N Forks, only the lead is softer, I use a tapered bridge reamer to chamfer the necks of cases. You can pick one up for $5-10 from a hardware store, and they are good for 22 to 50 cal. Lymans VLD reamer is essentially the same thing but with a bit more taper.

The nice thing about reaming vs expanding is once you've reamed the brass, it's good to go until you trim the length again. Also it doesn't work the brass as much.

MHC

284 is pretty much right except some of the M dies that I have will certainly overdo it. Just keep running the case into the die as you turn the die in 1/4 turn per time. Eventually you will feel the ledge that does the belling touch the mouth of the case. When you first feel this, try a bullet and check to see if the base of the bullet will enter freely without snagging. Sometimes it will be enough just before you can even see an actual bell, it's that slight. If you need more put more bell in it.

The only thing I have against excessive reaming or chamfering is that you are removing material that needs to be there when (if?) a crimp is needed. Ream away too much case mouth material and the crimp will be weak because the material at the mouth winds up too thin.

Mike