Does anyone have and recommendations for my New 586 4 inch barrel?

Galco Combat Master Belt Holster Leather

DeSantis Thumb Break Scabbard

Simply Rugged Holsters Sourdough pancake

Lobo Gunleather makes several that fit L frames

Simply Rugged sour dough pancake. I've got one for my 686 2.5".

IWB Milt Sparks VMII...

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why? why not?

I use a Remora with my 4" 686....works great. Hides very well as it keeps the gun close to the body.
A 4" L frame is a lot of gun to hide, not quite a t-shirt only rig... but I carry mine a lot when I can wear a 2nd shirt over it.

Carrying a 4" L-frame revolver can be a bit of a challenge. Concealment will require some thought. Comfort will require some thought.

My first recommendation would be a good pancake-style holster, worn strong-side slightly behind the point of the hip (roughly 4:00 position). The pancake design tends to conceal the profile of the handgun better than most other styles, while the fore-and-aft belt attachment points spread the weight over a larger area of the belt.

My second recommendation is to make sure you have a good solid gun belt to anchor the holstered handgun firmly in place. No holster can perform to optimum levels unless provided with a solid foundation on the body. Your 4" 586 will weigh in at about 2.5 lbs. loaded, so don't expect a department store belt to do the job.

Check out JMkydex
The JMCK IWB 3 for S&W 66