I don't think the ISP models were "Pre-39"s, if there even is such a critter, given that the adopted them in the late 60s. Looking at some of the descriptions of the AD/NDs above, I find it amazing that these are the first and only of which I have ever heard that were blamed on the pistol. ISP had a ton of them and shot a lot of ammo, and I do not recall ever hearing of them having trouble with ADs (as opposed to NDs). There are a lot of things I don't like about these pistols (DA/SA being the primary problem), but I don't recall any problems of the sort described.

ISP shot them so much that they became the source of a lot of the improvements S&W made from the initial 39s to what would become the 3rd generation pistols. They also were the reason for the first really good 9mm JHP ammo, the 115 +P+, and its successor, the 127 +P+. Both rounds had very good records in shootings. I bought a couple cases of the 115 +P+ on the contract in the early 90s and carried it for duty ammo for quite a while. It was so cheap in that volume I did not even buy practice/training ammo. I also carried the 127 +P+ later, and still have some of each left as I recall.

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NHI, 10-8.