Montana - lengthening 2 1/2" chambers does not "make it somewhat easier to find shells." It may make someone believe that the gun is now OK for SAAMI factory loads or feel less guilty about using them. Chamber length is a relatively minor consideration compared to load pressure. Low pressure loads in 2 3/4" cases work just fine in 2 1/2" chambers. The issue with high pressure is not likely to be a burst, rather it is likely that the gun will be knocked off face in a shorter time than with proper service pressure shells. Thus, it is very important that the gunsmith pay close attention to the guns on-face condition. If the gun has not been shot too many times and Purdeys being on the robust side, the gun may have gotten away with it. I'm of the opinion that kdross has figured out the proper diet for such guns. Hope this works out for you, Ken.
I beg to differ with your rebuttal, but we are both right in essence. As someone who has used reloads as well as factory ammo, I know it is much easier to find low pressure shells in lengths longer than 2 1/2 inches. And, often cheaper. Depending on the gun, 2 3/4 shells may work fine in 2 1/2 inch chambers or not. The British reproofed guns with lengthened chambers I own came from shooters/shops where the work was done to stop worrying about hulls hanging up or whether lengthened forcing cones had taken the gun out of proof in the first place. Suitable pressures and so on are items to be aware of no matter the chamber length.
