I am pretty sure the rugs that are advertised for 4" revolvers are a tad too small for the big N frame. Also, I don't want one so large the pistol will get lost in it.
In the early 1990s I got a great Bore-Store bag for large/med size 4-6" barrel handguns. It has a treated fabric that protects the firearm & it's easy to use(note; it is NOT secured) so it's not ideal for regular storage around kids or untrained adults.
Be aware that you DO NOT want to use a rug to store the gun in. Only use it for transporting the gun. Many guns have become rusted hulks from storing in rugs and padded cases.