It can be done and there are new production .357sig barrels that pop on the GB...
I'm pretty sure there was a thread about it here somewhere???
EDIT! The barrels that some times come up are not fit to your gun spficly... mind you every performance center gun and barrel is hand fit that Briley bushing out front is fit to THAT barrel... THE BARREL THAT YOU BUY MAY JUST DROP IN, BUT NEEDS TO BE CHECKED ALL THEY WAY AROUND!
With all due respect I'm saying that above because I would hate for someone to destroy their beautiful 3rd gen PC Gun..
I sent my entire gun (DPA5906) to Briley when I had a Threaded barrel made for it, just to be sure, I dident want to wreck the gun...