A new study from the FBI’s Training Division shows that overall, the 9mm Luger pistol round is the best option for law enforcement handguns, recommending departments shouldn’t switch their side arms to larger rounds considered by many to be more lethal.

Based in a combination of factors, including so-called “stopping power,” weight and availability, the FBI study shows that the 9mm round penetrates far enough, allows for shooters to carry more rounds, and is more widely available and less expensive than alternative rounds like the .45 ACP or .40 Smith & Wesson.

“Most of what is ‘common knowledge’ with ammunition and its effects on the human target are rooted in myth and folklore. … Handgun stopping power is simply a myth,” the FBI said in its report. “There is little to no noticeable difference in the wound tracks between premium line law Auto enforcement projectiles from 9mm Luger through the .45 Auto.”

The study — which was concluded May 6 but has just been leaked online — comes as the U.S. military is considering a new handgun to replace its decades-old Beretta M9 9mm pistol, and some law enforcement agencies are debating whether to outfit their officers with heavier rounds. The findings may also help civilian gun owners decide which handgun to purchase for self defense and concealed carry.

Arguing “stopping power” only applies to shots to the central nervous system (the head or neck), the FBI says modern 9mm Luger ammunition retains most of the ballistic characteristics and penetration power as its larger-caliber brethren, but is easier to control and leads to more accurate shots.

The study shows most law enforcement shootings result in only about 30 percent of the rounds hitting their target.

“The Ballistic Research Facility has conducted a test which compares similar sized Glock pistols in both .40 S&W and 9mm calibers, to determine if more accurate and faster hits are achievable with one versus the other,” the FBI says. “To date, the majority of the study participants have shot more quickly and more accurately with 9mm caliber Glock pistols. The 9mm provides struggling shooters the best chance of success while improving the speed and accuracy of the most skilled shooters.”

So when the skill of the shooter — with many agencies and even civilian shooters unable to train on a consistent basis — is a factor, there’s no shortcut in shooting a larger-caliber round.

“While some law enforcement agencies have transitioned to larger calibers from the 9mm Luger in recent years, they do so at the expense of reduced magazine capacity, more felt recoil, and given adequate projectile selection, no discernible increase in terminal performance,” the study says. “Given the above realities and the fact that numerous ammunition manufacturers now make 9mm Luger service ammunition with outstanding premium line law enforcement projectiles, the move to 9mm Luger can now be viewed as a decided advantage for our armed law enforcement personnel.”