The SEAL Model 66 revolvers are shown in Richard Marchinko's book.
They had Hogue rubber Mono-Grips fitted.

The holsters appeared to be an upright type nylon shoulder holster fastened tightly to their vests.

The Teams now have huge support organizations including world class gunsmiths.
They can have any modifications they need to their guns, so some probably have modded S&W revolvers, or even several with different mods.