10mm Auto Ammo

What is 10mm Auto?

The 10mm Auto has an unusually complicated history. Jeff Cooper — the father of modern pistol technique — helped develop the concept in the early 1980s. The cartridge was developed by Norma Precision and first chambered in the Bren Ten pistol in 1983, a gun designed by Dornaus & Dixon that became better known for its appearance in Miami Vice than for commercial success.

The FBI adopted 10mm Auto in 1989 after the Miami Shootout (1986) demonstrated the inadequacy of the agency’s .38 Special revolvers. Field agents found full-power 10mm difficult to control, so the FBI downloaded the loads to reduce recoil — the “FBI lite” specification. Those downloaded loads had nearly identical ballistics to a 9mm in a larger, heavier gun. The FBI eventually contracted with Smith & Wesson to develop a shorter cartridge based on the 10mm case: the .40 S&W, introduced in 1990.

10mm faded commercially after that. It survived in Glock 20s and Colt Delta Elites, mostly in the hands of outdoorsmen who needed a powerful semi-auto for bear country. The 2010s brought renewed interest as hunters and hikers rediscovered what full-power 10mm actually does — and companies like Buffalo Bore and Underwood built their reputations on loading it properly.

Full power vs downloaded: the critical distinction

Two completely different products are sold under the “10mm” label:

Full power (what 10mm was designed to be):

• 180gr JHP: 1,300–1,350 fps, 676–728 ft-lbs
• 200gr hard cast: 1,200–1,250 fps, 640–694 ft-lbs
• 220gr hard cast: 1,100–1,150 fps, 591–645 ft-lbs

Downloaded / “FBI lite” (what many commercial brands sell):

• 180gr JHP: 1,050–1,150 fps, 440–528 ft-lbs
• Similar to or weaker than .40 S&W

If you buy 10mm from Winchester, Remington, or Federal standard lines, you’re often getting downloaded ammo. For full power, buy from Buffalo Bore, Underwood, DoubleTap, or Federal’s Solid Core/Hunting lines. The box should say something like “1,300 fps” or “FULL POWER” — or just check the listed velocity.

Running downloaded 10mm in a gun sized and weighted for full power means you’re carrying extra weight for no performance benefit over a .40 S&W. Get the right ammo.

Ballistics: what full-power 10mm actually does

From a 4.6” barrel (Glock 20):

A full-power 180gr 10mm load carries ~2x the muzzle energy of standard 9mm. That gap is real and matters for hunting and bear defense. It doesn’t matter for home defense scenarios where 9mm and .45 ACP are both adequate.

Bear defense: what actually works

The 10mm gets recommended for bear defense because it’s the most powerful semi-auto cartridge that fits in a practical carry gun. For brown bear and grizzly:

• Use hard cast, not JHP. You need to penetrate skull and heavy shoulder muscle to reach the CNS. JHPs expand and stop short. Hard cast bullets don’t expand — they penetrate.
• 200–220gr at 1,100+ fps is the minimum. Less than that and you’re in .44 Special territory.
• The Glock 20 is the standard platform because it’s reliable, holds 15+1, and is light enough to actually carry.

Bear spray remains statistically more effective at stopping bear charges than any firearm, but in Alaska, brown bear country requires backup. The 10mm with hard cast loads is the most credible semi-auto option.

10mm vs .44 Magnum vs .357 Magnum

Against bears, the .44 Magnum has more energy. The 10mm’s advantage is semi-auto capacity — 15+1 vs 6 rounds if a bear charges. Both are defensive tools, not hunting loads for that scenario.

Brand guide

Buffalo Bore 220gr Hard Cast — the standard for bear country. 1,100 fps, deep penetration, no expansion. ~$1.20–1.80/rd.

Underwood 200gr Hard Cast — 1,200 fps, slightly faster than Buffalo Bore in the same weight class. Consistent, quality control. ~$1.00–1.50/rd.

Hornady XTP 180gr — the most tested 10mm hunting JHP. 1,300 fps from a 4.6” barrel. Controlled expansion, good penetration. ~$0.75–1.00/rd.

Federal Trophy Bonded 180gr — bonded construction, designed for hunting, reliable expansion through heavy muscle. ~$1.00–1.30/rd.

Federal HST 200gr — the defensive standard, controlled expansion at 10mm velocities, designed to meet FBI protocol at these energy levels. ~$0.90–1.20/rd.

Blazer Brass 180gr FMJ — cheapest reliable practice ammo. Downloaded (~1,100 fps), but fine for training. ~$0.50–0.70/rd.

DoubleTap 200gr WFN — Wide Flat Nose hard cast, full power, legitimate penetration. ~$1.00–1.40/rd.

Price guide (2025–2026)

Firearms chambered in 10mm Auto

Semi-automatic:

• Glock 20 (full-size, 15+1) — the community standard; most reliable 10mm platform
• Glock 29 (compact, 10+1) — same reliability, more concealable
• Glock 40 MOS (long slide, 6” barrel) — adds ~80 fps vs G20, optic-ready, the hunting standard
• Colt Delta Elite — 1911 format, 8+1, original 10mm platform
• Sig Sauer P220 10mm — double-action/single-action, 8+1
• Springfield XD-M 10mm — 15+1, full size
• Rock Island Armory 1911 10mm — budget 1911 platform, reliable

Hunting-specific builds: The Glock 40 MOS with a Leupold DeltaPoint Pro is the most common hunting 10mm setup — long slide for velocity, optic-ready, 15+1 capacity.