RE: Porting your own barrel
There is lots of hype out there about porting and muzzel brakes. I have been experimenting with brake design for 15 years and have even enlisted the help of an engineer who did supper sonic wind tunnel testing and found out some very intresting things. First and most important is that angled ports and such do not help at all. Gas moving above the speed of sound does not like to turn corners so all we are concerned with is the frontal areas of the holes. The speed of sound does go up with tempriture however this has little effect on the gasses inside a barrel. The biggest reason the porting on a shot gun barrel does so little is the barrel is thin enough that you have very little frontal area for the gas to work against. As for trying to do it on your own, unless you are a machineist and know about stress and pressures it would be best to farm the job out to some one who does or you at best could mess up your gun.