10mm vs 45 ACP: 37,500 psi Against 21,000
10mm is rated to 37,500 psi against 45 ACP’s 21,000, and that near-double pressure gap is the real difference between the two rounds.
Last updated: September 21, 2026 · Originally published September 9, 2026
The 10mm Auto is loaded to 37,500 psi. The .45 Automatic is loaded to 21,000. That is a 79 per cent difference in working pressure between two cartridges that share a test barrel length, a rifling twist and a headspace datum. Almost everything people argue about here comes down to that gap and what each cartridge does with it.
What I want you to walk away with
- Maximum average pressure: 10mm Auto 37,500 psi, .45 Auto 21,000 psi, .45 Auto +P 23,000 psi. Even the +P .45 is well short of a standard 10mm.
- SAAMI standardizes no 10mm +P. The name does not exist in the standard, though 9mm, .38 Special, .38 Super and .45 Auto all have one.
- The matched comparison — Federal’s HST in both — is 567 ft-lb against 404, from identical 5-inch test barrels. About 40 per cent more energy.
- Published 10mm velocities span 1,100 to 1,700 fps across the catalog. No other common handgun cartridge is loaded across that kind of range.
- Glock publishes the same 4.61-inch barrel and 8.07-inch overall length for its 10mm and .45 pistols, at 15 rounds against 13.
Here’s how I read this chart
Every number in this table is a published figure, copied from the source named underneath it — none of it is my own measurement. Read across a row to compare one entry, and down a column to compare them all on the same measure.
The specifications, side by side
| Specification | 10mm Auto | .45 Auto | .45 Auto +P |
|---|---|---|---|
| SAAMI name | 10mm Automatic | 45 Automatic | 45 Automatic +P |
| Bullet diameter, jacketed | .4005 in | .4520 in | .4520 in |
| Bullet diameter, lead | — | .4530 in | .4530 in |
| Case length | .992 in | .898 in | .898 in |
| Cartridge overall length | 1.240 – 1.260 in | 1.190 – 1.275 in | same |
| Rim / head diameter | .425 in | .480 in | same |
| Head to datum | .2000 in — identical for both cartridges | ||
| Rifling | 6 grooves, 1 turn in 16 in, left hand, marked optional — identical for both | ||
| Maximum average pressure | 37,500 psi | 21,000 psi | 23,000 psi |
| Maximum average pressure, crusher | Not established | 18,000 CUP | Not established |
| Proof, minimum average | 50,500 psi | 31,000 psi (+P proof used for both) | |
| Proof, maximum average | 54,000 psi | 33,000 psi | |
| Test barrel | 5.000 in — identical for both cartridges | ||
The shared rows are what make this comparison unusually clean. Same test barrel length, same rifling, same headspace datum — so when two makers publish a 10mm figure and a .45 figure from the standard barrel, they really are measuring the same way. Most cartridge comparisons cannot say that.
One row deserves its own note. The .45 Automatic’s standard proof load is marked obsolete in the standard, with the instruction to use the +P proof loads instead. The cartridge is proofed at 31,000 to 33,000 psi — which is still below the 10mm’s service pressure of 37,500.
Quick answers
Is it .45 ACP or .45 Auto?
SAAMI’s name is 45 Automatic, abbreviated 45 Auto. The string “ACP” does not appear anywhere in the pistol and revolver standard. “.45 ACP” is recognized only in SAAMI’s separate names document, which lists it as an accepted equivalent. Both are correct in ordinary use; only one is the standard’s name. The 10mm Auto, by contrast, has no listed alternate names at all.
Can I shoot .40 S&W in a 10mm pistol?
SAAMI does not endorse it. Its interchangeability document is a closed list — “limited to only the following” — of about twenty chambers, and neither 10mm Automatic nor .40 S&W appears on it. The two cartridges do share several case dimensions, including rim thickness, extractor groove diameter and head-to-datum, but the 10mm case is 0.142 inches longer and the document’s standing warning applies: fitting a chamber is not the same as being safe in it.
Is there a 10mm +P?
Not as a standard. SAAMI lists +P versions of the 9mm Luger, .38 Special, .38 Super and .45 Automatic. There is no 10mm Auto +P entry. Loads marketed above the ordinary catalog level are being made to the maker’s own specification, within the one 37,500 psi ceiling.
Which has more capacity?
The 10mm, in the one place a maker publishes a like-for-like. Glock’s own specification pages give the G20 in 10mm a standard 15-round magazine and the G21 in .45 Auto a standard 13, with both pistols published at the same 4.61-inch barrel and 8.07-inch overall length.
Which kicks harder?
No maker publishes a recoil figure for either. Buffalo Bore, which loads both heavily, addresses the question head-on and refuses to answer it: “recoil is highly subjective and there is no formula or definitive number that can be assigned.”
The comparison that is actually like-for-like
Here’s how I read this chart
On the left, one maker’s defensive line — Federal HST — loaded in five different cartridges. Because it is one product family tested the same way, the bars are directly comparable in a way that mixing brands never is; the 10mm bar is the tallest by a clear margin. On the right, every published 10mm muzzle velocity I could find, sorted from mildest to hottest. The right panel is the point most 10mm arguments miss: the cartridge is not one thing, it is a 600 fps range.
| Caliber | Item | Weight | Velocity | Energy | Barrel |
|---|---|---|---|---|---|
| 10mm Auto | P10HST1S | 200 gr | 1,130 fps | 567 ft-lb | 5 in |
| .45 Auto +P | P45HST1S | 230 gr | 950 fps | 461 ft-lb | 5 in |
| .45 Auto | P45HST2S | 230 gr | 890 fps | 404 ft-lb | 5 in |
| .40 S&W | P40HST1S | 180 gr | 1,010 fps | 408 ft-lb | 4 in |
| 9mm Luger | P9HST1S | 124 gr | 1,150 fps | 364 ft-lb | 4 in |
One bullet design, one company, one testing method: 567 against 404 foot-pounds, both from a 5-inch barrel. That is the honest headline number, and it is about 40 per cent.
The +P row narrows it. Federal’s .45 Auto +P is the same 230-grain HST at 950 fps instead of 890 — 461 ft-lb — which closes roughly a third of the gap for 2,000 psi more pressure. Speer’s Gold Dot line tells the same story from a different catalog: 10mm 200-grain at 537 ft-lb against .45 Auto 230-grain at 404, both from 5-inch barrels. Hornady’s Critical Duty pairs a 175-grain 10mm at 523 ft-lb against a 220-grain .45 Auto +P at 464.
Every matched pairing I could find lands in the same place: the 10mm leads by something between 13 and 40 per cent depending on which .45 load you set against it, and the .45’s +P option is what decides where in that band you land.
The 10mm is not one cartridge
This is the part that makes the comparison genuinely hard, and the part most articles skip. The .45 Automatic’s published catalog is narrow — most defensive loads sit between 850 and 1,050 fps, with a handful of light +P bullets above that. The 10mm’s is not narrow at all.
| Load | Weight | Velocity | Energy | Where it sits |
|---|---|---|---|---|
| Federal Punch / Speer Gold Dot | 200 gr | 1,100 fps | 537 ft-lb | The mild end of the catalog |
| Federal HST | 200 gr | 1,130 fps | 567 ft-lb | Mainstream defensive |
| Hornady Critical Duty | 175 gr | 1,160 fps | 523 ft-lb | Mainstream defensive |
| Federal Fusion / Solid Core | 200 gr | 1,200 fps | 639 ft-lb | Hunting-weight factory |
| Buffalo Bore Heavy Outdoorsman | 220 gr hard cast | 1,200 fps | 703 ft-lb | Woods loads |
| Buffalo Bore Heavy | 180 gr | 1,350 fps | 728 ft-lb | Woods loads |
| Underwood XTP | 155 gr | 1,500 fps | 775 ft-lb | Highest published energy |
| Underwood Xtreme Defender | 115 gr | 1,700 fps | 738 ft-lb | Highest published velocity |
From 537 to 775 foot-pounds is a bigger spread than the entire distance between a mainstream 10mm and a mainstream .45. So “10mm versus .45 ACP” is not really one question. A Federal Punch 10mm and a Federal Punch .45 are two loads a beginner could reasonably choose between. An Underwood 115-grain at 1,700 fps and a 230-grain .45 at 890 are not in the same conversation at all.
Worth knowing why the mild end exists. When the FBI adopted the 10mm in 1989, the Bureau’s own account was that “the high chamber pressures generated by the commercial loadings, with the resultant heavy recoil and muzzle blast, tended to offset the otherwise excellent performance of the round” — so the FBI handloaded a 180-grain bullet down to 950 fps, which it recorded as having “dramatically reduced recoil and muzzle blast.” The downloaded 10mm is as old as the cartridge’s service career.
What the FBI’s 1989 testing recorded
The FBI’s adoption of the 10mm was written up in its own Law Enforcement Bulletin in November 1989 and is public on a Department of Justice server. It is the only side-by-side institutional test of these two cartridges I could find published by the organization that ran it.
On penetration, against a 12-inch minimum: “10mm-39 shots out of 40 (97.5%) .45-37 shots out of 40 (92.5%) 9mm-27 shots out of 40 (67.5%)”. On accuracy: the 10mm “was by far the most accurate round tested, consistently providing one hole 10-shot groups at 25 yards of less than an inch (0.77” average)… By contrast, the 9mm averaged 2.3″ and the .45 averaged 2″.” And the conclusion: “The best performing round within the parameters of the FBI’s test protocol was the 10mm.”
Three things to hold alongside that. It is a 1989 document, and both cartridges have thirty-five years of bullet development since. The article states its test barrels for the 10mm and .45 were 6 inches, where the current standard specifies 5 — so those figures are not directly comparable with today’s catalog numbers. And the FBI’s own later position, in its 2014 memo, is that “there is little to no noticeable difference in the wound tracks between premium line law enforcement projectiles from 9mm Luger through the .45 Auto.” The Bureau tested its way to the 10mm and then, over the following twenty-five years, tested its way back out of it.
The bear question, answered honestly
The 10mm’s modern reputation is as a woods and bear-defense cartridge. I went looking for an agency that endorses it and found none.
The National Park Service’s “Firearms for Personal Protection” material for Wrangell-St. Elias covers legality and bear spray and names no cartridge. The NPS “Bear Spray & Firearms” article names no cartridge. Alaska Department of Fish and Game’s firearms and ammunition guidance discusses rifle calibers — .338 Winchester Magnum, .30-06, .270 — and no handgun cartridge at all.
So the case for the 10mm in bear country rests on the published ballistics above and on the makers’ own product naming, not on any agency saying so. Buffalo Bore calls a load “Outdoorsman”; that is marketing, and it is honest marketing, but it is not a recommendation from anyone who manages bears.
What nobody publishes
- Recoil — for either cartridge, from any maker, with Buffalo Bore publishing a short article on why it will not.
- Expansion, penetration or wound figures — absent from every Federal, Speer, Hornady, Remington, Underwood and Buffalo Bore page I checked.
- Test barrel length from Underwood, Buffalo Bore or Remington — so the hottest published 10mm figures cannot be compared cleanly with the mainstream ones.
- A SAAMI 10mm +P standard — confirmed absent, not merely unfound.
- Copper crusher pressures for the 10mm Auto or the .45 Auto +P — the standard records them as never established.
- Any agency recommendation of a handgun cartridge for bear defense.
Where to go next
9mm vs 45 ACP covers the .45 against the cartridge that displaced it in service use, 44 Magnum ammo covers the revolver cartridge the 10mm is usually weighed against for woods carry, and my caliber comparison chart puts all four beside each other. For field carry and bear-country gear, Popular Outdoorsman covers the outdoor side.
Sources
- ANSI/SAAMI Z299.3-2022 centerfire pistol and revolver standard — 10mm Automatic and 45 Automatic / 45 Automatic +P cartridge and chamber drawings, velocity and pressure tables, proof tables, test barrel drawings and gauge tables
- SAAMI, Generally Accepted Firearms and Ammunition Interchangeability, 8 October 2021; and Generally Accepted Cartridge and Chamber Names, same date
- Federal Personal Defense HST, Punch, Fusion, Solid Core, Swift A-Frame, Terminal Ascent and Trophy Bonded product pages; Speer Gold Dot; Hornady Critical Duty items 91256 and 90926; Remington Core-Lokt Handgun and Golden Saber Bonded
- Buffalo Bore 10mm and .45 ACP category pages, plus its published articles on felt recoil and SAAMI specification; Underwood Ammo 10mm and .45 ACP product pages
- Glock specification pages for the G20 Gen5 MOS and G21 Gen5 MOS
- FBI Law Enforcement Bulletin, November 1989, “The FBI’s 10mm Pistol” by J.C. Hall, NCJ 122334, via the Office of Justice Programs; FBI Training Division 2014 justification memo as published in a municipal council records system
- National Park Service, Wrangell-St. Elias “Firearms for Personal Protection” and “Bear Spray & Firearms”; Alaska Department of Fish and Game, “Firearms and Ammunition for Hunting in Alaska”
Ammunition reference desk
Three charts readers come back to: what a round costs today, what a cartridge name really measures, and what shipping and tax add.
| .22 LR | 6.59¢ |
| 9mm Luger | 26.98¢ |
| 5.56 NATO | 44.95¢ |
| .270 Win | .278 in |
| .30-30 Win | .309 in |
| .308 Win | .309 in |
| Case price | $269.80 |
| Shipping and tax | +$18.89 |
| Per round | 28.87¢ |
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