Pretty much what i figured Trying to find out the top end. Plan on shooting 2 1/2 " anyways. Probably wiil use bismuth when non-toxic is required. Unless i can swing 2 guns

Bell also tested 2 3/4" shells in 2 1/2" chambered guns and pressure only went up about 500 - can't remember exactly the pressure but not enough to worry about if you're loading low pressure loads to start with.

2 3/4" sheels in 2 5/8" chamber 12 Gauge
 

Deleted. Wrong forum

I want to thank the responders to this post. That is as good an explanation to pressures and Parker barrels as I have seen. The true knowledge expressed on this sight is amazing.

there is also a parker set of barrels marked plain steel.....charlie

Parker and other makers drew no distinction for strength between fluid steel and pattern welded steel barrels. I don't either.

I suggest you study the SAAMI specifications, that will tell you what the maximum
chamber pressure that factory ammo is supposed to generate. Without reviewing again, I think it's 11,500 for 2 3/4" 12ga shells, such as magnum loads.

TPS in the barrels and chambers chapter has a table showing service and proof loads for Parkers of various gauges and chamber lengths. If I remember correctly , 12 ga 2 5/8 chambers are 10,200 psi service load maximum . These are for guns in as new barrel condition. I follow these loads. There are many commercial loads that meet the Parker service load limit and many that do not. So yes, a person can shoot modern loads, but not other modern loads without exceeding design standards.

Suggest you study both documents.

Of course a person can always shoot lesser loads to save shoulders, hinge joints, and stocks.

What Bruce said.

A Parker Service and Proof Load table was published in the 1930s and reproduced in the The Parker Story p. 515.
12g 2 3/4” shell Service Pressure is 10,500 psi. Definitive proof used 7.53 Drams Black Powder and 2 oz. shot with a pressure of 15,900 psi. The pressure was no doubt measured using LUP and modern transducer values would be 10-14% higher, or more than 17,500 psi.

LTC Calvin Goddard reported the same numbers in “Army Ordnance”, 1934. He wrote that Parker followed the SAAMI standards of that period: 13,700 psi proof, 9500 psi service for 2 5/8" chamber; 15,900 psi proof, 10,500 psi service for 2 3/4" chamber (by LUP) + 10-14% for modern transducer measurement.

Of course by the 30s the remaining "time bomb" Damascus rough forged tubes had been destroyed :(

Parker- America's Finest Shotgun by Peter H. Johnson
All of these barrels and tubes used by the Parker were made in and around Liege, Belgium. So far as the knowledge of still-living Parker officials goes, none were ever successfully made in the United States. These barrels, which were imported as "rough tubes," with a low tariff were reasonable in price and very beautiful; but with the advent of progressive burning powder after World War I they were doomed as they were unsafe to use with these new and more powerful powders. So at that time Parker Brothers, certainly not to be left behind by such a plain and inescapable necessity, discontinued the use of them and started making their own barrels from the latest American steel that had been developed during World War I. It is interesting but hardly surprising to note that when Parker changed from figured barrels to those made of fluid steel the factory officials destroyed under a hammer all the barrels that they still had in inventory rather than run the risk of these barrels ever being used.