This is going to get a bit involved, but hang on. If you want to know what's exactly "correct" with S&W grips - it gets a bit involved. But in recompense for paying attention to the lecture, it is profusely illustrated.
Here are some pics to show you the "target" grips and the "service" Magna grips. The target grips are shown on a Model 67 (photo 2), but are identical to what would have shipped on a 66-1. 66-1's were made from 1977 to 1981 or 2 I think.
To be correct, your grips should have "silver washers" on the inside. Prior to that, the post-war grips had black washers (up to about 1973). In the mid/late 80s, they went to "no" washers on the inside. The third picture shows "silver" washers on the inside (on J-frame grips, but this is what the washer should look like).
66-1s could be had with Magna grips - but it would be a special order. The pictured 66-1 4" (photo 1) came with the Magna grips pictured. Many did ship with Magna grips, especially those destined as duty guns - as many were. These are "service" or "PC" magnas as the bottoms are rounded and sculpted, to "print" less under clothes (PC means "plain clothes"). For shooting I like the older "square butt" magnas, like came on earlier K frames and all N frames Magnas.
Many find the Target grips too large - they are frequently called "oversize targets." The diamonds also tend to bite the palm with full power magnum loads. An option many shooters who like factory grips choose is to add a black rubber Pachmayr grip adapter, or an aluminum Tyler T Grip coupled with Magna stocks. This is pictured in photo 4, on a 66-1 2.5" with some aftermarket fake ivory "Magna style" grips. Note that Tyler and Pachmayr adapters are different between round a square butt models.
Photo 5 shows what would be a correct factory accessory grip for your gun, a "smooth target" it is no smaller than the checkered target, but fits more comfortably in the hand, and does not bite as hard. They are more attractive, rarer, and more expensive, but worth it to me. They are pictured on a 686, but are correct to a 66-1 period, also.
I believe I had lots of K factory grips for sale - google "s&w grips" in the accessories classifieds if you want.
Always happy to help get a nice S&W back into factory form.
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