Interesting discussion. I did a test on my GM barrel, a .45 with 60" twist. I used a .445" ball and 10 ounce denim, which I measure with MY tools at .0225", compressed.
I worked up an accuracy load which gave me 1/2" to 3/4", 5 shot groups at 50 yards.
I coned the muzzle to a depth of approximately 1", straight taper. I used the same load as before and my groups opened to 2" to 2 1/2" at 50 yards. I cut 7/8" inch off the end of the barrel and re-crowned it as we, Taylor and I have been noting here for a number of years.
If you want a cone - GREAT - have at it. If you want the best accuracy from your rifle, don't cone it- that is my opinion on coning.
Further note about coning. LB bought a .40 from a maker here on ALR. I don't remember who the maker was. This barrel was coned. LB asked me to cast him up some balls as he didn't want to do this work - I assume. I gave some some of my .400" x .400" balls from a Lyman DC mould. Using the same normal 10 ounce patch I was using in my .40 with a .398" bore, he complained the balls were too big and that they were exceptionally difficult to get started in his .400: bore that was coned - USING A SHORT STARTER.
I was easily loading them in my .40 with the same patch material. What it comes down to, is the angles of the crown vs. cone. The cone lengthens the reducing surface, causing more drag/friction (length of engagement) when attempting to compress, ie: FORM an oversized load into the bore. I tested this with his rifle and yes - that is what was happening - the .0225" patch and .400" ball was almost impossible to load in the coned bore.
If you have read about bullet DRAWING using dies from CORBIN, you would know the drawing angle is very short, but rounded and perfectly smooth. This is the angles we are putting on our muzzles - the crown's length is no longer than 1/8".
The long taper creating excessive drag also showed up when we were reducing jacketed .375" bullets to .366". I made a die that had a short 'polished' radius from the shank .375" down to .366". The force needed is about the same as FL sizing large cases, using a normal Lyman case sizing press. With a long tapered die, like a normal Lee bullet sizing die, it is impossible to do the same job, as the friction is too great and will damage the die and or press. If using these dies, a 3-die set can be used. it takes that many of long taper-designed dies to do the job of one with a proper bullet drawing die.
This diatribe explains the relationship between a long taper as in a cone, to a short radiused crown & how they differ so radically in bullet seating.
Reason, it seems for the ease that is reported for coning might be this.
I submit the load combinations guys are finding easy to load in a cone, are barely,if any tighter than what guys who need to wipe their bores often, use in barrels without cones. A cone would make a thin patched load even easier to load - perhaps. Improve accuracy? Not in my tests.
Now, it is possible that a cone will give the same accuracy as an croned barrel - it is possible, but I sincerely doubt it will with the same load combination. With that statement, I am hinting that with more experimentation, a load possibly could be found to shoot as well in a coned barrel, as one which I like to refer to as properly crowned.