The Lovinsior Herstal double barrel shotgun, serial number P1K329,Êhas a 2 3/4 inch barrel.Ê It was made between 1952 and 1960.
Try a 1300 barrel
Start with this site www.midwestgunworks.com
Check the receiver and barrel
"Your" Winchester Model 21 Double Barrel Shotgun was manufactured in 1933, giving it an age of 77 years, as of 2010.
Please include the model number of your Winchester shotgun to get a correct answer to your question along with the serial number.
Your Winchester model 1911SL(self Loading)shotgun was first made in the year 1911.
Any barrel will fit only if you replace the tube also to a conventional 1300 tube.
That would depend on the type of barrel with the shotgun(plain,matte solid rib,or vent rib barrel)if a poly choke is present on the end of the barrel,and what condition the shotgun is in.
The Winchester Model 21 Grand American 3-barrel cased set. Bert H.