The fit is exact though a bit of the muzzle is exposed. My opinion is that they make a basic pattern for similar sized revolvers like the S&W 586/686 that has a 4" barrel where the Ruger's is 4.2". That's it. A good liner was a must for me because the GP100 is blued rather than stainless. I found and bought through Amazon.
![Wink ;-)](./images/smilies/icon_wink.gif)