I'm new to the revolver world, so please bear with me. I want to replace my front sight with a SDM fiber optic. When I measure the revolver the factory sight is .156 above the raised sight base and .3125 above the top of the barrel. The SDM is available in .250 and .300 height.
It looks like the SDM measurement must be from the barrrel ?
If I use the .300 I will need to lower my rear sight a bit ?
I think the .250 would require too much rear travel ?

The stock 617 front blade is a .168. It's measured from the tall end of the blade to the base it's pinned in. The .250 fiber optic is too tall even with the tallest (.196) rear blade. Hi-Viz makes a fiber optic .168 front. I tried one, it gave a lousy sight picture beacause the rear blade doesn't have a deep enough notch. I ended up with a .200 front (black patridge) and a .160 rear. The .200 front being a cut down .228.

Thanks for the info. I'll be going close to the local gunsmith shop next week, I'm going to stop in and ask him what he can do. I read another post re the sight is not predrilled and concerns about drilling the front sight. Where I am, I do not have access to a drill press. I would not try to do it by hand.

I agree. I much prefer using a drill press. Helps prevent OOPS's.