The internals are not the same, The HD has the same internals as the HD5-20x50. glass is better, but I have never felt wanting for more or shorted when using the non HD 3-15, so much so that I bought a second one. I have not looked through the 10x but I have 3 5-20x 50 HD and 2 3-15x42, the 3-15 are not HD but are still a very nice scope. I would probably go a 3-15x42 be fore I went an 10x HD or a !0x non HD. 3-15 is great for hunting and no problem out to 1000yrds and more.I love the 5-20x50 HD's. A lot of people keep asking for a 3-15x42 HD. I looked through 2 vortex viper LRH 4-16 side by side to my 3-15 SWFA and the SWFA's we noticeably better glass, and the higher you cranked the power the more you noticed, the vortex was hazy compared to the SWFA, and they were 2 brand new vortex at the same time so I ruled out just a bad scope.they are defiantly built tougher than the vortex viper too, both tube and turrets.