Pro/Carbine barrel will not come out.....

That bolt you're referring to Boydster is called the pinch bolt because it locks the barrel in place after you screw the barrel in to keep the barrel from shooting loose. The barrel threads in the receiver have a slit cut down them. When you tighten the pinch bolt it closes the gap of that slit reducing the diameter of the barrel threads and thereby pinching the barrel. The bolt must be completely loose to screw in the barrel. A helpful hint: I screw  my barrel in all the way with the pinch bolt loose. I then slowly tighten the pinch bolt until there is just a very slight resistance on the barrel when I try to unscrew it. It works great and I have never had my barrel shoot loose on my P/C or my P/L. This way you don't have to carry an allen wrench with you to loosen the pinch bolt every time you need to remove the barrel (carrying allen wrenches are a no-no in scenario games or tourneys).
The hole in the front stock can be enlarged to accept other barrels, but it must be done carefully because the plastic there is not very thick. I used my Dremel tool and a sanding drum set on medium speed. Sanding at too high a speed will melt the plastic. It also helps to first remove the front stock and separate it into its two halves. I can now fit Smart Parts All American barrels through the front stock and it still looks good. The hump in the Smart Parts barrel where the front and back section are joined is a snug squeeze, but the barrels go in and out OK. Hope this helps.

yes yes, I'm quite aware that the internals need be removed before polishing anything. I'm just wondering how he did it. The body is not cut in halves like the m98.

About the barrel now. I have to say that I like the stock one quite a bit. I swear it shoots straighter than my Ultralite. The stock barrel + Zap Rec series is what I use, and it shoots incredibly straight. Seems strange, the two seemingly worst items shooting darts.

Thanks for informing be about the receivers being clamped down. That explains it. I was a bit confused when I had to have the bolt almost spinning loosely to get the barrel unthreaded. It shouldn't have the be that loose. But now that I know about the whole clamping thing, it makes sense. I adjusted it to where I'm barely able to get the barrel out. Any tighter and it's stuck.

With the barrel out, I noticed it the same type as the A-5 stock barrel. Just longer. They should have used the same on as the P/C on the A-5, that extra length REALLY adds accuracy. I still can't believe how accurate it's shooting.

Thanks for the helps guys.

Hey thanks for the tip. I never would of thought of that. I polished my 98c with steel wool by hand...

And I think I have everything you listed up there in my garage. I'm going to give the receiver a try with that polishing.

However my barrel is just too good the way it is. I don't want to fix an already good thing.

Again, thanks for the help.