So what do we actually know (and confirming these dates was a challenge)?
Rumors about the steel mandate for waterfowl picked up about 1976.
The Olin-Kodensha Winchester Model 23 was introduced in 1978.
During the 79'- 80'waterfowl season, some steel shot zones were established.
500 Heavy Duck models were manufactured in 1984.
More lead bans were put in place for the 87'-88' season.
It is reported that the Kodensha barrels are chrome lined.
The Model 23 IS marked "Winchester Proof Steel".
AFAIK Winchester never claimed the Model 23 was "steel shot compatible" in 1984 or later.
IF the barrels are indeed 4140 WPS and chrome lined there would be little difference from "modern" 4140 steel shot compatible barrels, the use of which would of course require the appropriate choke.
I believe however there would be legitimate concern regarding rib separation and head of the stock splitting with 3" 1 1/4 oz. at 1450 fps steel loads. Remington Nitro Steel has a 2 3/4" 1 1/8 oz. 4s at 1390 fps
https://www.remington.com/ammunition/shotshell/waterfowl-loads/nitro-steel-high-velocityBill: what are those "earlier years"? At some point the steel load wads were manufactured thicker and tougher, but I don't know when.
