In many of our ammo tests, you will see the use of wet phone books as a substitute for ordinance gelatin. Granted, the phone book is not a scientifically accepted test medium, but it does yield consistent and practical results with either solid or expanding projectiles. One of these standard, metro-sized soaking wet phone books generally translate into 8”-10” of penetration in calibrated ordinance gelatin when comparing the same load from the same gun. This is a good bit less than the FBI’s 12” minimum standard. So, if a round fails to penetrate one of these books, it certainly fails the FBI standards.
To keep things in proper perspective, keep in mind that the FBI standard was in-part developed to weed out cartridges that failed to function properly after passing through intermediate barriers such as auto safety glass, and car doors. Therefore, if you are an LEO, these standards are no less than a doctrine to live by. For civilian defensive use though, a round that fails the FBI test is not necessarily a useless defensive round. Keep in mind that most civilians are much less likely to be blasting bad guys through car doors with much regularity. Even if your particular ammo only delivers 10″ of penetration in ballistic gel, that’s still a nasty 10″ puncture wound. And, if delivered to the right spot, it will probably do the job just fine.