I still own one GP100 as well. Its the 3 inch. I used to own a few 4 inchers (and one 6 inch as well) Here is a pic of parts of my former collection, the 6 inch had been sold at that point. And I noticed in close comparison that the top strap on the 3 incher is thinner than one th 4 incher Here is a my former 3 incher (have another one now, I was forced int he past to sell off guns to support unemployment) And here is one of my former 4 inch GPs Not sure how apparent it in in these pics.. BUt if you hold both together its very noticeable that the top strap on the 3 inch gun is less thick and this also applied to the front of the fram where the barrels screws in. Now clearly less metal helps reduce weight and thats not a bad thing.. (I suspect the 4+ ounces difference in weight between the 4 inch and the 3 inch is only in part due to shorter barrel) Now I want to speculate (or maybe be told by the Revolver Gurus on here), is the reason for this : a) A design choice by Ruger since they expect the 3 inchers to generate less pressure than the 4 inch guns when using same ammo? (I know this is theoretically so, but surely the difference must be miniscule.. I see the ballistic chart for GP100 3 inch vs 4 inch velocities w/ same ammo and it appears the 3 inch gives up very little in velocity).? 2) A design choice by Ruger ...Since they expect the 3 incher to be less likely to be used for hunting and therefore less likely to see the hottest loads? 3) A design choice by Ruger to reinforce bringing down the weight since the 3 inch might actually be conceivably concealed carried at some point (which is nigh impossible with the 4 inch)..? Helping reduce the weight a tad more might complement the lesser length for conceal carry? 4) A design choice by Ruger since a shorter barrel when dropped imposes less impact force on its mounting point in the frame ? (due to combination of less weight and less leverage by the barrel tip on the frame)..? 5) A choice by Ruger since the 3 inch came out later and by then they had a lot of extra data and realized how much over-designed the 4+6 inch really were? (BTW the forcing cone and the cylinder are identical among all 3 barrels lengths I have owned (3,4,6) and the frame strap and front part of the frame where the barrel is screwed in are the same thickness on the 6 inch as the 4 inch.) Anyone more versed in Revolver science than me care to comment on which if any of these 5 factors might be the source of the difference?