Hodgdon also states the maximum charge for 357 Magnum with a 158 grain XTP is 9.5 grains of HS-6. So, in a 38 special case the volume is a bit less than the 357 Magnum so that would tend to cause a more rapid rise in pressure and a bit higher pressure. However 7.2 grains is well below the listed maximum for 357 Magnum. IMO it would probably not be at all harmful to the 686 to shoot these loads, most likely they will behave a moderately mild 357 Magnum. Probably the only potential for a problem might be sticking cases or perhaps some split cases. Considering what Elmer Keith and others were doing with the 38 special back in the 1930's my hunch is that the cases won't actually be harmed at all.

However if you want to play it safe then just break them down. I once had about 300 round of 45 ACP get water logged in a corner of my baement that flooded due to a blocked downspout. Since I don't enjoy the thought of a Squib ruining a range day I broke all 300 down with a whack a mole bullet puller and it held up just fine. Fact is it's still in good shape 2 years later. BTW, only found 6 rounds with water in the powder but 6 is still too many, now I pay close attention to my downspouts in the Fall and the Spring.