All,

As is often said, "pistols are pistols and rifles are rifles". But at what point does a pistol caliber become a rifle caliber?

Let's compare four self-defense loads:

Federal LE Tactical HST JHP
9mm Luger +P
124 gr
1200 fps
396 ft-lbs
https://www.luckygunner.com/9mm-p-12...st-1000-rounds

Federal LE Tactical HST JHP
.45 ACP
230 gr
950 fps
461 ft-lbs
https://www.luckygunner.com/45-acp-2...nt-1000-rounds

Federal LE Tactical SP
.223 Remington
55 gr
3220 fps
1266 ft-lbs
https://www.luckygunner.com/223-rem-...tru-500-rounds

Federal Fusion SP
7.62x39
123 gr
2350 fps
1508 ft-lbs
https://www.luckygunner.com/7-62x39m...sion-20-rounds

MUZZLE ENERGY --> LETHALITY

There's a clear difference in muzzle energy. The .223 bullet is less than half the size of the 9mm bullet, but because it's going nearly 3x as fast, it's going to be more lethal:


https://www.ar15.com/ammo/project/Se...ense_Ammo_FAQ/

Is there a point at which a pistol caliber becomes a rifle caliber in terms of muzzle energy? Is there an accepted standard, e.g. "Any bullet that delivers more than 1000 foot-pounds energy is no longer a pistol caliber, but a rifle caliber"?

SPEED --> FRAGMENTATION

There's a clear difference in feet per second. It's been well-documented that misses from faster rifle bullets are less likely to pose a danger to others:

"Statements are made that the shotgun or pistol should be used because of the over-penetration problem with 5.56 carbine ammunition. This could not be further from the truth. If you conduct a little research you will find that numerous law enforcement departments, to include the FBI, have proven this to be false in most cases. The fact of the matter is that many of these bullets will penetrate numerous walls, but standard 5.56 loadings are the least of your worries when compared to pistol and shotgun fodder, which continue to take top honors in the category of over-penetration." US Army Sergeant Major Lamb (former Delta/CAG)
https://www.americanrifleman.org/art...xperts-opinion

"Common pistol rounds easily penetrated all 4 walls spaced out at room distances. This is a critical issue. Think about the inside of your house and imagine if you shot through 4 walls. Could you hit a loved one? Know your target and what is behind it....The 5.56 rounds deviated greatly from the original flight path once they started tumbling. This occurred after the second wall." Old_Painless (certified Pistol, Rifle, Shotgun, Personal Firearms Defense, and Home Firearms Safety Instructor)
http://www.theboxotruth.com/the-box-...sulated-walls/

"Proponents of the pistol for home defense like to think that because it’s 'just' a pistol round, overpenetration really won’t be an issue. Such is not the case. Drywall sheets and hollow-core doors (which are what you’ll find in the majority of homes and apartments in this country) offer almost no resistance to bullets....For years many people just assumed they knew what would happen to a rifle bullet fired indoors—it would go through every wall available and then exit the building. While armor-piercing and FMJ ammunition is specifically designed to do this, extensive testing has shown that light, extremely fast-moving .223 projectiles (including FMJs) often fragment when they hit a barrier as soft as thin plywood." James Tarr (former police officer; contributing editor for Guns and Ammo)
http://www.gunsandammo.com/ammo/long...fense-caliber/

"The .223/5.56 is moving at around 3,000 feet per second, and while it isn’t magic bullet, it’s a far cry better than any pistol round. Another advantage of the .223/5.56 is its limited penetration. The shape and velocity of the round cause it to immediately expend or dissipate its energy once it strikes something." Tiger McKee (adjunct instructor at Thunder Ranch)
https://gundigest.com/reviews/ar-15-...e-defense-guns

"The pistol rounds were seemingly unaffected by the drywall and/or wood barriers. There was no observable deviation or fragmentation of the 9mm projectiles. You’d be safe counting on a pistol round to keep going, and going, and going. After all, premium pistol ammunition is designed to expand, and lose energy, when striking liquid-based targets—not walls. The full metal jacket .223 rounds tended to tumble rather than break apart when they encountered barriers." Tom McHale (contributor at AmmoLand and OutdoorHub)
http://www.outdoorhub.com/stories/20...ration-issues/

"FBI and Independent Testing Has Consistently Shown .223/5.56 NATO Fired From AR-15’s Do Not Over Penetrate More Than Pistol/Shotgun." Caleb Lee (NRA Certified Basic Pistol & Personal Protection Inside The Home Instructor)
http://preparedgunowners.com/2016/07...ation-testing/

"Since all of the 5.56 mm/.223 bullets fired through the interior wall had significantly less penetration than 9 mm, .40 S&W, .45 ACP, and 12 ga. shotgun projectiles which were fired through an interior wall, stray 5.56 mm/.223 bullets seem to offer a reduced risk of injuring innocent bystanders and an inherent reduced risk of civil litigation in situations where bullets miss their intended target and enter or exit structures. As such, 5.56mm/.223 caliber weapons may be safer to use in CQB situations and crowded urban environments than service caliber handguns or 12 ga. weapons." Dr. Gary Williams (ballistics expert)
http://www.recoilweb.com/ar-vs-shotg...#ixzz4zCOCPykZ
Those who subscribe to this principle believe that if you're concerned about overpenetration, the faster (and smaller) .223 is better for home defense than the slower (and bigger) 7.62x39 (and of course, better than even slower [and even bigger] pistol rounds).

Is there a point at which a pistol caliber starts to behave like a rifle caliber in terms of speed? Is there an accepted standard, e.g. "Any bullet that travels more than 2000 feet per second is no longer a pistol caliber, but a rifle caliber"?

Respectfully,
butlers