That's always seemed like a strange loading to me. Most older .38 revolvers and some if the newer aren't up to +P loads. otoh, a SP101 with a 2.25" barrel is hardly bulkier than the traditional .38 snubbie and handles ++P++, aka .357 Magnum.
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Better alloys, better hear treatments, and, in the case of some newer revolvers, better structural design.
And Ruger does it with investment-cast frames.