FYI. A quick review on JPoint 4 (4 MOA dot) This is a really light unit, may be close to the weight of a quarter dollar coin. It is designed to mount with a couple of screws on to a thin platform. You can buy various platforms for various gun designs, even for picatinny rails. This allows you to move it to different guns, from sight on handguns to functioning even as quick sight on rifles. Be aware, however, platforms are sold separately. Maximum profile height is about a quarter's height above the platform, which is not much at all, and doesn't interfere with the overall look of the gun as much as the more obnoxious red-dot sight in tube design. Aside from the attachment screws, there are three Allen screws, two horizontal ones on each side and a vertical one for vertical adjustment. One of the horizontal ones, on the left side as you look thru the sight, is not to be messed with, because it provides a horizontal reference location. JPoint includes a dial that fits on the provided Allen wrench to give a better feel for adjustments. Important: there is no ON/OFF switch. The commonly found cr2032 battery provides the power. Some think it is on all the time drawing little current, some think the protective hard plastic cap turns it off in storage. I mounted it on my 6" barreled G20 shooting high powered rounds (750 ft-lbs plus). And it functions VERY well enduring the recoil of 10mm rounds. Note that the add't weight of the 6" barrel tamed some recoil compared to a stock G20 barrel. Rested on a fixed cradle, I can consistently hit orange clay disc at 20 yards. I'm sure many of you can do better! Overall, it doesn't add much to the weight of the gun, or to profile of the gun (in my view). The whole gun holsters easily. The tiny dot is bright in day time, and may be a bit too bright at night. If you are willing to be set back by some $300+, this thing can work well on a Mark III, or any Ruger. I wanted to point this out since I've seen so many Mark III looks ruined by the attachment of a big red dot tube sight! Those tube sights also ruin the weight balance of the gun, holstering ability.