Bryan,
I looked the gun up in the "Book" and Dean is spot on about this Parkers 26" barrels. I have my fathers Trojan 20 gauge and it is a dream to shoot. 2 3/4" shells ar fine to shoot even in 2 1/2" chambers. Again, Dean advised you well about the 2 1/2" shells. However if you keep the 2 3/4" shells to 7/8 oz of shot at 1200 feet per second or under you will be equally served.
www.rstshells.com has some lovely loads that are very friendly to these old guns and to young and old shoulders alike.
Harry
Hybrid Mode