Odd. Folks have been taking game up to the size of deer with the Lee conical bullets for decades.
Did deer and coyotes suddenly grow armor plating?
The fact is -- accuracy is more important than conical bullet design. Being able to place the conical bullet exactly where it should be is what counts.
Even the humble round ball will take deer, if placed properly.
Marksmanship, and not taking impossibly long shots, are critical. I would not take any shots against deer beyond 25 or 30 yards. Black powder bullets have comparatively low velocity, and shed that velocity rapidly. This means a loss of striking energy.
Most black powder revolvers have rather rudimentary sights, making accurate placement difficult. The Ruger Old Army and Remington styled revolvers with modern sights are exceptions, but their projectiles still shed velocity quickly.
Stalking skills often come into play as well. The shooter may have to wriggle on his belly for some distance to get close enough to deliver an accurate, killing shot.
Shooting at the range, calmly and with normal breathing, is different from hunting. You may very well be huffing and puffing when you align the sights on a deer, and excited with "Buck Fever."
The best practice is to put up targets in the woods along a one-mile path, jog to within 25 yards of each target, and give yourself 5 seconds to align sights and shoot. This will show exhibit your capabilities and limitations.
Hunting from a stand is different, of course, but you may still have to contend with the excitability of Buck Fever.
The Lee .450" 200 gr. conical bullet is made for most .44 cap and ball revolvers. The Lee .457", 220 gr. bullet is made for the Ruger Old Army.
The larger, heavier bullet may be very difficult to seat in non-Ruger guns. There is no advantage in using it, outside of the Ruger.
Some of the most accurate groups I've obtained have been with the Lee .450" 200 gr. conical in my Uberti-made reproduction of the Remington 1858.
Here are the details:
Goex FFFG – 26.4 grains from flask spout
Lee 200 gr. conical, cast of soft lead
Lubricated with Gatofeo No. 1 lube (search the net for recipe)
Remington No. 11 cap, pinched
No wad beneath bullet
20 yards, measured
Group – 1-1/2 inches vertical, ¾ inch horizontal
Unknown velocity