IHMSA is international HANDGUN metallic silhouette association. You need to shoot in the rilfe competitions for that. Those fall under NRA smallbore. You would be in the unlimited class I believe with that rifle.
The 686 could be shot in Field Pistol. You really dont need that much gun but it can be used. The most common gun in Field Pistol is the 22 hornet. I have shot revos out there. Just find a club and go shoot.