According to the wiki, the "Dismember only" onHit effect that the Ratslayer has alerts everyone in the vicinity of the target hit to your presence, which is obviously a bad thing if you're trying to be sneaky. I didn't see another fix for this so I made one. This simple .esp just changes the onHit effect to the same one as the Varmint Rifle, which means the Rayslayer will no longer dismember limbs or make them explode, which is unfortunate, but you will no longer (hopefully) be detected when you shouldn't be.
Incompatabilities:
I imagine it would be incompatible with anything that alters the Ratslayer.
Installation:
Place the file in your "\fallout new vegas\data" folder, open the launcher, click Data files, tick the box next to RatslayerFix.esp and click okay.
Uninstallation:
Delete the file(RatslayerFix.esp) from your "\fallout new vegas\data" folder.
Incompatabilities:
I imagine it would be incompatible with anything that alters the Ratslayer.
Installation:
Place the file in your "\fallout new vegas\data" folder, open the launcher, click Data files, tick the box next to RatslayerFix.esp and click okay.
Uninstallation:
Delete the file(RatslayerFix.esp) from your "\fallout new vegas\data" folder.