GP-100 Mods
There are a lot of mods possible.
Sights:
Front- I added a Millett blaze orange front. The orange is a lot brighter than other painted sights. Another thought is the Express Sights Big Dot or Standard Dot with or without tritium. One can use either the Express Sights rear or Bowen makes a compatible rear. Also, you can order the 4 color sight set for the Ruger Redhawk. They will fit the slot but will need to be filed down in height to work.
Rear- Millett makes rear sights. On mine I put a Bowen rear sight on and as noted the sight picture is improved greatly due to the flat rear sighting plain. The notch is also wider than the Millett (I have a Millett on a S&W). Bowen offers both a Rough Country sight (several configurations) and another replacement with the normal screwdriver click adjustable manner of operation. I believe Gary Reeder makes an all steel replacement rear sight as well.
Hammer- I have not done this but Jim Stroh (and others) offer to build up the thumb pad on the hammer along what would be called in "Target Hammer" on a S&W.
Barrel-again I have not done this but one can have the forward portion of the underlug milled off. The article mentioned below had this done. Another option would be to cut back the barrel or change to a different length. Unknown by most is that at one time Ruger produced some 3" barrel adjustable sighted GP-100's. It is possible to cut back the barrel and retain the replaceable front sight.
Trigger - I had mine contoured and polished by a gunsmith to mirror bright for double action shooting and removing of any sharp edges.
Chamfering the cylinder-if you plan on using speedloaders this will help some. Be certain the gunsmith does NOT chamfer the extractor portion. Essentially the rear of the charge holes is beveled with a small 45 degree angle.
One can also have the cylinder machined for moon clips. As machined the gun will fire in the normal manner without moon clips and eject or you can use full moons.
The last I knew for $450 Dave Clements would modify the GP-100 to fire 10mm on moon clips. His website is at:
http://www.clementscustomguns.com/default.htm The gun will also fire .40 S&W, of course. It is a 6 shot conversion.
Grips-I ordered Hogue Kingwood grips with the grip cap and without the finger grooves to give more latitude in hand placement. For me the finger grooves never seem to fit correctly. Your mileage may vary. Other grips available from:
Herretts
http://www.herrett-stocks.com/
Hogue
http://www.hogueauction.com/
Badger
http://www.badgercustomgrips.com/ruger_pistol_grips.php
Excaliber
http://www.grips4guns.com/revolver/ruger/gp100.html
Eagle
http://www,eagkegrips.com
Altamont (I think made a rosewood finger groove for the gold trigger/hammer limited production models)
Ruger - at one time Ruger offered via Internet an all wood grip for the GP-100
Jeweling-I had the sides of the hammer polished and jeweled for cosmetic purposes only.
Action work-I had the action tuned by a gunsmith and since have played with various Wolff spring weights. In mine I use the 9 pound mainspring and 8 pound trigger spring. I have had no misfires but then headspace is near minimum as is endshake and firing pin protrusion near .050" (some Rugers have a lot less leading to misfires). The net result is about a 7.75 pound double action and 2.5 pound single action pull. The tuning by the gunsmith usually reduces the single action notch on the hammer to eliminate trigger creep and maybe changing a few angles to reduce the single action pull. This should be done with a jig and having some knowledge or one can get pushoff. Since having this done correspondence with Apex Tactical (see below) indicates they might get the double action a bit lower (he claimed 5 pounds on race gun-his S&W 627s with his hammer run around 4-4.5 pounds) maybe in the high 6's or so.
Here is a link to an article on a C&S modified GP-100:
http://www.cylinder-slide.com/gp100.shtml
There are a number of places that work on GP-100s besides Cylinder & Slide. Some are:
Apex
http://www.apextactical.com/
Gemini
http://www.geminicustoms.com/Projects.htm
Magnaport
http://www.magnaport.com/
Action Works
http://www.theactionworks.com/browning.htm
Clements
http://www.clementscustomguns.com/default.htm
just to name a few. As to holster I use a Tauris with thumbreak. Here is a link:
http://www.tsparksolutions.com/taurisholsters/reinhighride.cfm
It cost a bit more than buying off the rack but one can order with or without lining, with or without thumb break and/or tension screw and get the belt slots to match belt width. Most mass produced holsters seem to be set up for a 1.75" belt and most of my pants take either a 1.25 or 1.5" belt so this was a consideration. Turnaround was about a month. There are a plethora of holster makers out there that make all sorts of styles for the GP.