Anytime I ever tried a countersink in the muzzle, I got chatter. Maybe Taylor's trick of a piece of cardstock under the bit would have helped.
Now I use a lathe, so all this is out the window. Don't need no stinkin countersinks.
Nor any chatter either.
Acer
I have a lathe too, a pretty good one actually. However, it takes a lot of time to *properly* set up a barrel. So for ML crowns I tend to use the lathe to MAKE tools to do the crowns. I still think that a 100-120 degree single flute will do a good job of roughing in a crown with hand tools.
I just upgraded my lathe from a rather down in the mouth Clausing to a much better LeBlond.
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Using the lathe to make tools that require no machine set up saves a lot of time in the long run.
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This was made to do a crown in my 16 bore hunting rifle. The cutting agent is wet or dry paper applied with double stick carpet tape. It can be a pain if you work it too hard but but does a nice job and can be used with an electric drill if one feels the need. Removable pilot is aluminum.
I am going to make one for the smaller bores next.
Don't get me wrong, I like using a lathe to cut crowns, works great, very precise. But its time consuming.
I did a lot of BPCR crowns in the lathe and still would. But to do it right needs dial indicators and plug gauges at BOTH ENDS with a "cats head" at the far end of the spindle bore to get the bore running true. All this just to break the lands to an angle at the muzzle but it looks really precise, is precise and I was doing work for finicky BPCR match shooters, national champions etc.
A ML crown really needs to be more complex to work well and I generally use more than one tool. Shoot the rifle then go back and change if needed. I could spend an hour(s?) in just in setups.
I have used stones in the past as well and they will work well. I have polished crowns with wet or dry on a countersink. I have made them with a large flat head screw for a countersunk hole with lapping compound. I have tried lots of stuff over the years and it will ALL WORK if done carefully.
But a tool like that above will do a good grown that is square with the bore and with 600 grit as a final cut makes a very smooth surface.
Using this then another similar tool to put about 1/8" long shallower angle "funnel" on the lands greatly eases loading. This has allowed me to shoot a significantly thicker patch in the 16. Its been crowned about 3 times now as I keep fine tuning it.
Dan