I'm a great Ruger fan, but I have no use for the GP-100. The balance is horrendous and even the 4-inch model feels like I'm holding a hammer! I have a few Security-Sixes and they're outstanding. The S&W 686 is, in my view, is the best of the three models mentioned in the OP.
I love the Colt Python. It's a well crafted pistol that has a proven record of accuracy. The bluing is legendary; however, the downside is its small pawl/hand, which wears too quickly and requires frequent re-timing of the gun. This can be fixed by hard chroming the pawl, which increases wear significantly, but it's a pain.
The 686 was designed to meet or beat the Python and, in my opinion, it succeeds. It's still a bit heavy for my taste, but the balance is superb. The 4-inch model is ideal. The 686 costs far less than the Python, is built to exacting specifications, has an excellent action and an enviable reputation.
I'd love to give the thumbs up to the Ruger, but the Security-Six has been shown to shoot up to 30,000 hot magnum loads without the locking cylinder and other innovations. And I've never thought that one spring doing the work of two is better! It's hype. The gun also throws most of its weight forward by virtually eliminating the steel grip. It's a nub. In a survival situation, if you destroy the grip for whatever reason, that nub will be difficult to turn back into a grip. I realize this is a reach, but the balance of the gun isn't. The action of the GP-100 also is significantly inferior to those of both the Python and the 686 which, out of the box, are fabulous.
I'd love to have a Python, but if I lived in Alaska and needed a reliable .357, my choice would be the 686.
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