I did the same thing a while back, except I'm 3" #2 steel. My wife has a 20 gauge and when I couldn't find steel for her gun, I had to buy Bismuth. I examined the pellets from the bird she shot and I could see it deformed a bit, kinda like lead, probably giving it better knockdown power. I shoot enough shells that the $$ wouldn't pencil out very well for me to switch.
I also like steel for the fact that it doesn't tear up the meat like lead. Further, I rarely see a bird that is inedible due to damage from shotgun blast. I do see that with lead a time or two each season.
Woolly and Golden -- Here is some info that I've posted before that might be helpful.
When using steel loads on pheasants, it is best to go with loads that contain #2 or #3 steel pellets. Steel shot lethality research conducted on pheasants by Tom Roster showed #2 steel to be more effective (at all ranges) than either #6 or #4 steel. Yes, #4 or #6 steel loads will kill'em too, but a little extra pellet energy is a good thing on wild pheasants where shots are often taken at going-away angles and can get on the long side. The research also showed that #2 steel resulted in fewer cripples than both #6 and #4 steel; and Roster speculated that the #3 steel pellet would be a good compromise between pellet count and downrange energy.
Here are a few of my pattern numbers to give you an idea of how some #3 and #2 steel loads perform, in my guns/chokes anyway!
Patterning results from a 20-gauge Browning Citori with 28" Invector-plus barrels and Briley flush chokes (patterns average of five, 30" post-shot scribed circle, yardage taped muzzle to target, and in-shell pellet count average of five).
20 GA 3" WINCHESTER DRYLOK SUPER-X STEEL LOAD
1 oz #3 steel (145 pellets) @ 1330 fps
30 YARDS – SK / pattern 114 (78%)
30 YARDS – IC / pattern 123 (85%)
40 YARDS – IM / pattern 106 (73%)
40 YARDS – LF / pattern 110 (76%)
20 GA 3" REMINGTON NITRO-STEEL MAGNUM LOAD
1 oz #2 steel (118 pellets) @ 1330 fps
30 YARDS – SK / pattern 101 (86%)
30 YARDS – IC / pattern 105 (89%)
40 YARDS – IM / pattern 99 (84%)
40 YARDS – LF / pattern 102 (86%)
I shoot most of my pheasants with this 20-gauge O/U and I normally shoot a SK/IM choke combo when using these loads.
Patterning results from a 12-gauge Browning Citori with 28" Invector-plus barrels using Briley flush chokes (patterns average of five, 30" post-shot scribed circle, yardage taped muzzle to target, and in-shell pellet count average of five).
12 GA 2 3/4" REMINGTON SPORTSMAN HI-SPEED STEEL LOAD
1 1/8 oz #2 steel (139 pellets) @ 1375 fps
30 YARDS – SK / pattern 116 (83%)
30 YARDS – IC / pattern 129 (93%)
40 YARDS – LM / pattern 114 (82%)
40 YARDS – M / pattern 114 (82%)
50 YARDS – LF / pattern 100 (72%)
50 YARDS – F / pattern 106 (76%)
As you can see, there wasn't any difference between the LM and M chokes with this steel load at 40 yards, they both registered the same 5-shot pattern average! Patterning is the only way to know how your choke/load combo is really performing!
When I do shoot this 12-gauge O/U at pheasants I normally shoot a SK/M choke combo with this load.
Hope this helps, good luck!