Ruger GP100 Barrel Swap

[CommonHighrise]

The Gun: Ruger GP100 .357 magnum, stainless, 6.5" half-shroud barrel, factory sights.

The Mod: Swapping it out for a 4" full shrouded barrel.

I have pretty good mechanical skills, enough tools to be deemed 'adequate', and willing to take the time to do it right. Is a barrel swap something I can do myself? If not, would I be better off purchasing the barrel, and giving the gun to my local and trusted gunsmith, even though he has never done a GP100 barrel swap himself, or just sending the whole kit-n-kaboodle out to Ruger and let them take a couple weeks to do it at the factory?

Also, is anyone who is skilled in the dark arts of ballistics able to tell me just how much power Ill be losing from a magnum cartridge by dropping my barrel length? I know my current 125gr Win Gold Sabers are viable from the 4" barrel, but will there be a real let-off in power?

[Xringshooter]

If you have all the tools required then you probably can do it yourself. Be careful and take you time. That said, here is the most likely problems that may crop up. You get the barrel in and the front sights are not vertical, or you get it in, it's down tight, the sights are correct, you put it back together and the cylinder won't close (hits on the barrel) or the barre/cylinder gap is too much. In the above cases metal work will need to be done. In the first the shoulder will have to be turned down a very little bit so the front sight is perfectly vertical when the barrel is tight against the frame. In the second, the rear of the barrel will need to be shortened to get the correct barrel/cylinder gap (this also needs to be checked in #1) or it needs the shoulder turned to get both the sights and b/c gap correct. For the cost, even though you say the gunsmith has never worked on GP's before, I would advise either a smith or return to Ruger. This work really is general to any revolver that is getting a barrel swap be it a Smith, Ruger, Taurus, Colt, etc., the gunsmith should have or can easily get the correct tools to do the job.

You probably won't notice any change unless you chronograph the 6" barrel before the swap and the 4" after the swap using the exact same lot of ammo. Then you may see a slight decrease in the velocity which would equate to a little lost power but not that much.