USA – -(Ammoland.com)- The 10mm Auto, sometimes referred to as the “357 of the Auto Pistol World”, has experienced a resurgence of late. Since its development in the 1980s, the 10mm found sudden popularity only to stagnate and shrink, but now the 10 is back with more pistols and ammunition than ever before. With that increased popularity comes truths and myths surrounding the round . . .
Semi-automatic pistol rounds are generally power-limited. The size and shape of the round must fit into a practical grip. That limits how much lead and powder can be on board. Revolvers don’t have that problem and magnum cartridges have been the mainstay of handgun power since the beginning. But the 10mm promises magnum-like power in a semi-auto platform along with all the benefits of that platform: faster reloads, more ammunition before reloading, ect.
10mm Auto vs. 357 Magnum
There is talk about the 10 being as powerful as the 41 Magnum. This is all talk about pressure curves on a graph where the hottest 10mm met the lowest pressure 41 Magnum rounds. A fairer comparison for the 10mm is the original magnum cartridge, the 357 Magnum.
With that question in mind, it was time for my favorite past time—a ballistics gel test.
.357 Magnum A Brief History
By the 1920s, American law enforcement turned away from their various 32 caliber revolvers then common in service for the much more powerful 38 Special cartridge. Despite being high powered for its day, the 38 Special showed some weaknesses early in the Gangster-era. It didn’t always work when defeating obstacles like steel automobile bodies, auto glass, and surplus bullet proof vests worn by the up and coming motor bandits that used more force than finesse in their crimes.
Higher pressure 38 Special revolvers and larger handguns to handle the round resulted until it was decided to develop a brand-new cartridge, the slightly longer yet much more powerful 357 Magnum. The year was 1935 and it became the most powerful handgun cartridge of its time with a 158 grain bullet traveling at about 1400 feet per second. Magnum revolvers were favored by law enforcement for many years since until they were retired for increasingly reliable, higher capacity semi-automatic pistols. Even so, the 357 Magnum ammo remains popular and is a gold standard of handgun power.
10mm Auto Ammunition
As the magnum revolver was puffing along in the 1980s, there was a desire for a semi-automatic pistol with similar power. Thus the 10mm Auto was born, firing a 40 caliber bullet at the same speed as the 357 Magnum. In the aftermath of the 1986 Miami Shootout, the FBI sought to replace their 357 Magnum revolvers and lower-powered 9mm auto-pistols with the 10mm. It promised more power than the 9mm while being faster to reload than the revolvers in standard service at the time. It was found that the new 10mm pistols were hard to control and the round was downloaded and eventually necked down to make the 40 S&W round.
The 10mm fell into obscurity with few pistols and few ammunition makers producing for the round. But in 2018, demand is higher and the 10mm is finally getting its due as an excellent hunting and defensive cartridge.
The 357 Magnum and the 10mm Auto come in a variety of loadings, but the larger 40 caliber bullet of the 10mm affords it somewhat heavier projectiles in factory loads. The 10 is often found using 180 grain bullets while the 357 uses a 125 grain bullet. Heavy grain bear-type loads range up through 200 grains for the 10 and 180 with the 357, so there is much overlap.
10mm Auto vs. 357 Magnum : The Test
In our head to head contest, I selected the same brand of ammunition with as close to the same weight of bullet as possible. The guns selected are as close as possible in barrel length so as to not unfairly skew the results to one end of the camp to the other. Hornady offer’s their Custom line with a 158 grain XTP bullet for the 357 Magnum and a 155 grain XTP for the 10mm. While the 158 grain weight is fairly standard for a 357, the 155 grain bullet used in the 10mm is slightly light in its typical range.
The test firearms are the Glock 29 Gen 4 in 10mm and the Smith & Wesson Model 27 in 357 Magnum. The Glock sports a 3.77 inch barrel vs the 4 inch barrel on the Smith. This is as close as I could get in factory guns and ¼ of an inch won’t make much difference in velocity.
That was proven true when I fired both rounds through the chronograph on two separate occasions during two test runs of each ammunition. Despite having a shorter barrel, the 10mm was slightly faster.
Hornady Custom 10mm 155 grain XTP – 1345 feet per second
Hornady Custom 357 Magnum 158 grain XTP – 1264 feet per second
*five shot average of shots
On paper with these comparable loads, the 10mm is slightly faster with an 81 feet per second advantage. That is much when we are talking about handgun velocities. But how would that translate in ballistic gel?
I lined up a Clear Ballistics 10% ordinance gel block and got to work. The block was covered with four layers of denim, which is an FBI protocol. The optimal performance of a round is 12-18 inches of penetration to consider quartering shots, bone, ect. I started by firing the 357 Magnum round from close distance to assure a square hit. It zipped through the sixteen inch block. I needed to double up.
I added a second block, which caught the follow-up projectile. The 10mm had no such trouble as it was stopped in the first block.
The 10mm round expanded to .70 inch, flattening out impressively, and stopping at the 16 inch mark. The first five inches of its wound tract opened to an inch and a half before abruptly terminating into a straight path until the bullet came to rest.
The 357 Magnum’s smaller 9mm bullet mushroomed slightly to .54 inches and traversed 22 inches of gel. Both 357 Magnum tracts showed inch-wide cavities out to the first nine inches of the block.
The 357 Magnum over penetrated and did more damage further on than the 10mm, however the 10mm round dumped its energy into the first block with respectable damage just inside the entrance wound.
The 357 Magnum’s smaller diameter will make for an inherently longer projectile or higher ballistic coefficient. This allowed it to penetrate deeper despite its lower velocity. The greater penetration was also aided by the lack of deformation of the hollow-point due to that slightly lower velocity. The 10 performed as advertised and its extra velocity helped to flatten out the projectile.
So Who Wins?
We could go on to test a variety of different loadings of 10mm and 357 Magnum, but in this head to head taking into account as many variables to the experiment as possible what can be concluded is that both rounds live up to their respective reputations with much overlap between them depending on what load you choose.
After shooting both rounds through the chronograph, I was convinced that the 10mm would outperform the 357, given its velocity advantage with the same weight of bullet. What we got was a bullet that nearly doubled in diameter and violent expansion without overpenetration. The 357 exceeded the recommended maximum of eighteen inches.
However, it appears that the 357 Magnum’s damage was greater for a longer stretch of the wound than the 10. In the big picture, the 10mm will throw a slightly heavier bullet at the same speeds that the 357 will launch a lighter grain bullet. We can see in this head-to-head that the 10mm retains a very slight advantage in terms of energy, but the 357’s overall longer bullet gives it the edge for penetrating power.
The 10mm vs. 357 contest isn’t Mayweather vs McGregor. It is nearly too close to call—nearly. Like with any boxing match, there is more to the story and the opponents that is sometimes not taken into consideration.
It appears time is the 357’s best friend and why I give it the edge in the contest. You can find 357 Magnum revolvers readily—new and used. Any big box store that deals ammunition is bound to have 357 Magnum defensive ammunition. 10mm ammunition is hard to find and when you find it, it is often more expensive per box than 357s.
Many common 10mm loadings are weakly loaded compared to the round’s true potential and many off the shelf brands are seldom more powerful than the 40 S&W. Despite increasing demand, 10mm pistols are hard to find and they tend to cost a premium when found.
However, if you choose the 10 you gain the inherit advantages of automatic pistols, greater ammunition capacity and simpler reloads. No matter what platform you choose, I doubt you will be disappointed. Did I miss anything? Let me know which round you would choose in a 10mm Auto vs. 357 Magnum head to head?
About Terril Hebert:
Terril Hebert is a firearm writer native to south Louisiana. Under his motto-Guns, Never Politics-he tackles firearm and reloading topics both in print and on his Mark3smle YouTube channel, where he got his start. Terril has a soft spot for ballistics testing, pocket pistols, and French rifles. When he is not burning ammo, he is indulging his unhealthy wildlife photography obsession or working on his latest novel. Scourge of God, published in 2017. See more from Terril on youtube under Mark3smle