.40 S&W vs 10mm Auto: How They Differ and Why They Do Not Interchange

.40 S&W and 10mm Auto fire the same diameter bullet, but 10mm Auto has a longer case and a higher pressure limit, so it is the more powerful cartridge. .40 S&W was created in 1990 as a shortened 10mm that duplicated the FBI's reduced-power 10mm load in a 9mm-size pistol. Under SAAMI dimensions the 10mm case is 0.992 inch long and the .40 S&W case is 0.850 inch. The two are not interchangeable in normal pistols. We do not stock either one right now.

Where 10mm Auto came from

10mm Auto began as a concept promoted by firearms writer and trainer Jeff Cooper. The Swedish ammunition maker Norma developed the production cartridge, introduced in 1983, for the Bren Ten pistol from Dornaus & Dixon. Norma loaded it hotter than Cooper's original idea. The Bren Ten did not last, and Dornaus & Dixon closed in 1986, but the cartridge survived when other makers chambered pistols for it.

The FBI and the birth of .40 S&W

After the 1986 FBI Miami shootout, the Bureau studied handgun performance and selected the 10mm in 1989. Many agents found full-power 10mm recoil and muzzle blast hard to manage, so the FBI developed a reduced-velocity load, often called the 10mm FBI or 10mm Lite load. Smith & Wesson and Winchester then shortened the 10mm case to match that reduced performance in a cartridge that fit pistols the size of a 9mm. The result, .40 S&W, was introduced in 1990 with a 180 grain bullet.

Side by side

Spec (SAAMI)	.40 S&W	10mm Auto
Case length	0.850 in	0.992 in
Maximum average pressure	35,000 psi	37,500 psi

Both use the same bore diameter and a similar case head. The 10mm's longer case holds more powder, and its higher pressure limit lets full-power loads drive bullets noticeably faster. That makes 10mm a common choice for hunting handguns and for carry in country with large animals, while .40 S&W is a duty and defense cartridge in pistols the size of a 9mm.

Why they do not interchange

Most semi-automatic pistols in both calibers headspace on the case mouth, the front edge of the case. A 10mm round is too long to chamber in a .40 S&W pistol. A .40 S&W round is short enough to slide into a 10mm chamber, which is the dangerous direction: it is not held in the right position, which can cause misfires, failures to extract, or a round firing when it is not fully supported. Some revolvers and convertible pistols are built to handle both, but only when the maker says so. If the barrel says 10mm Auto, use 10mm Auto. If it says .40 S&W, use .40 S&W.

How to choose between them

• Use and recoil. .40 S&W suits a duty or carry pistol in a 9mm-size frame. Full-power 10mm suits a larger pistol for hunting or backcountry carry.
• Ammo choice. 10mm loads range from mild, .40-like loads to full power. Read the box velocity, not just the caliber.
• Heat and storage. In Phoenix, keep any ammunition indoors and out of parked cars and garages over the summer.

What we stock instead

We do not stock .40 S&W or 10mm Auto right now. Our handgun stock is 9mm Luger and 5.7x28mm. In 9mm we carry Speer Gold Dot LE Duty 124 grain +P (53617) and Speer Gold Dot LE Duty 147 grain (53619), in 50 to 1,000-round packs. Our 9mm ammo guide and 9mm +P vs standard pages explain the options. Browse 9mm Luger, law enforcement or all pistol ammo.

You must be 21 or older to order from us. Orders ship UPS Ground from Phoenix within 2 business days. Pickup in Phoenix is Monday to Friday, 9am to 5pm, with ID. Call 480-623-4515.

.40 S&W and 10mm questions

Is .40 S&W a short 10mm?

Yes, in effect. Smith & Wesson and Winchester shortened the 10mm Auto case to create .40 S&W in 1990. They share bullet diameter, but the cases differ in length and the two are not interchangeable in normal pistols.

Can I shoot .40 S&W in a 10mm pistol?

Not unless the gun's maker specifically approves it. In most 10mm pistols the shorter .40 case is not positioned correctly in the chamber, which can cause misfires or extraction problems. Use the cartridge marked on the barrel.

Which has more pressure, .40 S&W or 10mm?

10mm Auto. SAAMI sets its maximum average pressure at 37,500 psi, compared with 35,000 psi for .40 S&W. Its longer case also holds more powder.

Does Heisenberg Ammo sell .40 S&W or 10mm?

Not right now. We stock 9mm Luger Speer Gold Dot and 5.7x28mm for handguns. See our ammo FAQ for more.