Shoulder diameter of the 28 nos is roughly 0.528". Shoulder diameter of the 7mm prc is 0.517" which means you would need to set the barrel back a little over 2" and start over to remove the entire, larger diameter chamber of the PRC. Not real practical but possible if you have a relatively long shank on the barrel which i doubt there is.
also, many feel that setting a barrel back will refresh the throat and give you a new full barrel life, this is not the case at all. Your barrel has been heat tempered by firing it. In my experience, setting a barrel back will get you around 30-50% of the life back depending on the intensity or the original chamber. For example in my extreme wildcats, you can get 1000 rounds of useful accuracy life. If you completely removed the chamber and recut the chamber, you would likely only get 400 of so rounds on the next throat life and a third time often only gets you half that at most.
tested this with two of my extreme range rifles, one in my 7mm Allen Mag and the other in my 338 Allen Mag. The 7mm AM started with a 36" 1.250" straight cylinder barrel. The 338 AM used a 45" 1.750" straight cylinder barrel, yep that was a beast!!
put around 700 rounds through each and then cut back a full 2.5" off the 7mm breech and a full 3" off the 338 AM. Results after that were about 300 rounds of accuracy after the set back on each. Then i took another 2.5" off the 7mm AM and and another 2" off the 338. This time accuracy drop off was after only 100-200 rounds…..
you can extend the barrels useful life but its not by nearly as much as most think…..