The frames of the 686 and 686 Plus are identical. It is the cylinders that differ -- but not in overall size. The Plus has 7 holes instead of 6, which means thinner chamber walls; but, the bolt notches are located between the chambers, meaning in effect that the strength of the 7-shot cylinder at least equals the strength of the same-size cylinder having only 6 holes in it.

In short, there is no difference in strength between the two. Either is capable of handling a lifetime of shooting SAAMI-spec .357 ammo.

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Pisgah