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Article 10mm AUTO The Cartridge, The Myth, The Legend

By Overkill338, Jan 10, 2017 | | |
  1. Overkill338
    The 10mm Auto, it almost vanished into obscurity. The brainchild of Col. Jeff Cooper who set out to make a flatter shooting cartridge than his beloved .45 ACP. He wanted it to be able to push a 200 grain bullet to 1200 feet per second, and it was achieved by shorting a .30 Remington case, blowing out the walls so it would accept the bullet from the .38-40 Winchester, a .400" bullet. Basing a pistol off the CZ75 design, the Bren-Ten was born, but it came at a price. $500 was a lot of money in 1986 and the company ended up filing for bankruptcy. Luckily Colt decided to pick it up in 1987 and started producing a 1911 called the "Delta Elite". This pistol is part of the reason we still know about the 10mm today. The other reason is probably because agent Dove's 9mm bullet stopped one inch shy of Platt's heart in the Miami-FBI shootout (see 1986 FBI Miami Shootout). Some speculate that Dove and Grogan might have survived if that bullet had pushed one inch farther.

    GT 10mm 2.PNG

    So the FBI decided they needed more powerful handguns. They adopted the 10mm Auto, in its full power form, it puts it square between a .357 Magnum and a .41 Magnum. They started using Smith & Wesson 1076 pistols. They were a variant of the S&W 1026, except the 1076 had a 4.25" barrel and a frame mounted decocker vs the slide mounted decocker on the 1026.They also contracted H&K to build MP5's in 10mm for their "SWAT" style teams, and those are still in use today.

    After agents started using these new handguns, qualification scores dropped considerably compared to the old 9x19 pistols. The recoil of the full bore 10mm proved to be too much for most agents. They began testing with "Reduced Recoil" ammo to try to improve scores and make the guns more manageable. The request for the new ammunition was passed to Federal Cartridge. This is the loads that became known as "10mm Lite", and several makers still make loads in power range. Of course when they started using lighter loads, the pistols became reliability disabled. Smith & Wesson's solution was to take the case from 25mm to 22mm and they were still able to copy the performance of the FBI Lite loads. This new version of the cartridge became known as the .40 S&W, and it also fit in 9x19 size pistols, which let shooters with small hands handle them better, and qualification scores improved again. Law
    enforcement agencies all around the US adopted this new cartridge and it has enjoyed great success.

    The 10mm Auto has always been around in guns like the Glock 20, Glock 29, Colt Delta Elite and some more along the way. A lot of self defense handgun owners only ever considered the 10mm for a woods defense gun, when hiking or hunting. Everyone feared if used for self defense against human targets that over penetration would be a severe problem, hurting bystanders and going through walls. It wasn’t until ballistic gel testing started to become popular that people learned the faster you pushed a hollow point bullet the LESS it penetrated. It actually takes well-constructed hollow points to handle the full power of the 10mm Auto. Bullets like the bonded Speer Gold Dot and the Hornady XTP. This turns the big 10 into a great self-defense firearm. Underwood Ammo, Buffalo Bore, & Double Tap Ammo are great places to get ammo tuned to get full potential out of the 10mm, 180 grain bullets at 1300 feet per second, and 200 grainers at 1250. They also sell 200-220 grain hardcast ammo for woods defense against 4 legged critters out to put you down. Plus here in 2016, the 10 seems to be making a comeback. You've got the Glock 20/29/40 and the Delta Elite like before, but now Sig Sauer is making a P220 in 10mm, Dan Wesson is in the game, Kimber, Nighthawk, STI, and Tangfolio too.

    This isnt just about the 10mm's accomplishments as the cartridge itself. Let’s not forget it's children that it has given us and their success as well. The .40 S&W, probably still the most commonly used law enforcement cartridge. The .357 SIG, pushing a 125 grain bullet at 1350 1450 fps (depending on ammo used), and quickly nipping at the .40 S&W's heels, as tons of LE departments are adopting it. The 9x25 Dillion, this one seems to be just for fun, because there aren’t any .355" bullets that will hold up to its speed. 124 grain bullet at 1700

    So when you are in a gun shop glancing around and see a 10mm pistol, don’t just think of a cartridge that almost disappeared into firearm history. Think of how amazing the round is and maybe give it a chance, or at least be thankful for its offspring that citizens and LEO's carry every day. The 10mm Auto is here to stay, and there are those of us who like it, and love to feel that recoil of this amazing cartridge. For the hand loader it can be anything from a .40 S&W to something right up at the .41 Magnum. It's probably one of the most versatile cartridges in existence, just give it a chance.

    GT 10mm 1.PNG

Recent User Reviews

    "My 1st G-Series was a G20C..."
    Nice write up!

    Once you get used to the 10mm with stout ammo, (I have a LOT of Sig Elite, 180gr @ 1250fps) everything else feels like a pu$$ycat! :D Also got some Buffalo Bore and Underwood, when I'm feeling froggy ;) If that does not do it, I have an LWD longslide for my G21, it's a 460 Rowland Conversion.

    How about an article on the Rowland?


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  1. k0mit
    I just got my first Glock, a G29. Can't wait to get to the range but that won't be for a couple more days.
    I got the bug for 10mm when Colt came out with the Delta Elite in the late 80s, but ended up going with .44 Mag instead. Now, I'm finding I don't enjoy the big .44 as much as I did in my younger days, so finally gave in to that 10mm itch that's been nagging me for thirty years. :)
  2. Vague17
    Alas, there is no mention of Dornaus and Dixon who put their reputations and fortunes on the line to bring the Bren Ten and the 10mm Auto into production. In particular, it was Mike Dixon who finalized the specifications for the 10mm Auto. Cooper took the glory but not any responsibility for making the new pistol and cartridge a reality. Here is a link to an article about the beginnings of the 10mm Auto:·s-670-40-amotfors-sweden/
  3. Kevin Schmersal
    Love this round. I have the G20, G40, and soon the G29.
  4. rangerjd
    Great article, I love my G20 with SF frame. It has become my full time woods gun and home defense gun. It shoots incredibly well. Still saving up for my G29.
  5. medezyner
    Good article. I was a die-hard .45 acp fan; tons of load options, controllable recoil, makes big holes, etc. Then it happened, I got the 10mm bug. Wanted to get into handgun hunting with an auto and from there it was a no-brainer. Bought a G20 and love it. Cant wait to hunt with it and has been my EDC since Christmas. The only down-side to the purchase is I cant stop buying toys for it: sights, 6" barrel, scope and now a reloading setup! Jez, where does it stop?
      jmohme and Overkill338 like this.
  6. ironrides
    My G20 10 mm doesn't kick much more then my Glock 19 9mm in my opinion. Excellent round with tons of ! Its not a 44 mag but ill take the increased ammo capacity and reduced recoil id take it to the hills for bear protection over the 44 mag. The bullet placement is better with reduced recoil. With 15 rounds I would feel better with my G20 then a 44 magnum. Over two feet of penetration in Ballistics gel with the correct round also helps me rest better knowing that its going to make it to critical areas when needed.
      bmrtoyo, Overkill338 and jmohme like this.
    1. jmohme
      I tend to agree with you. I have no doubt that I would have quicker follow up shots with my G20 than I would with a 44 wheel gun. And with quicker follow ups, I suspect that I could fire off more rounds with it before I became a meal for said bear.
      As far as recoil goes, though I feel a noticeable , but quite manageable increase, and that is just with 180 gr practice ammo.
      What ammo are you shooting?

      I have not received my Underwoods yet. I am curious as to how much kick they produce.
      Overkill338 likes this.
  7. Borg Warner
    Quote: "Nice write up. I just entered the 10mm world with a new gen 4 G20.
    I've only had it out once and put 100 rounds of off the shelf ammo through it, so I don't have enough experience with it to comment much. I do look forward to learning what this caliber has to offer"

    I agree that this was a good write up an d I look forward to the article on the 45 GAP. The 10mm has a great deal to offer if you're willing to learn to reload. Factory ammo is standardized at 1050 fps for a 200 grain bullet. The original Norma load for the 10mm was a 200 grain bullet at 1200 fps.

    Lesser bullet weights are proportionately "downloaded" with the only exceptions being the Grizzly Ammunition company's 180 grain JHP @ 1300 fps and the Winchester Silvertip 175 grain Jhp @ 1250.

    Lighter bullet weights will develop more velocity but velocity is only one component of ballistics. Everyone understands velocity because all you need to know about it is that a higher number is "Better" than a lower number. Reloading also gives you the ability to create reduced loads for teaching family members how to shoot.
      Overkill338 likes this.
    1. Overkill338
      The 45 GAP article should go live today or in the morning. Whenever Austin has time to post them.
  8. Grovenator
    It's on the radar for me.
      ironrides and Overkill338 like this.
  9. SmokelessPowder
    10mm components are ready available except for cheap brass. I'm sure it would be much more popular if you could get once fired brass cheap.
      Overkill338 likes this.
    1. View previous replies...
    2. Borg Warner
      Just today I found a source for once-fired 10mm brass for about half the price of new brass. 10mm Auto :$15.00 per 100 $75.00 per 500 Mixed Head-Stamps May contain both brass and nickel finish.

      Here's the link:
      Diamond K brass:

      10mm Auto :$15.00 per 100 $75.00 per 500
    3. Borg Warner
      Borg Warner

      Just today I found a source for once-fired 10mm brass for about half the price of new brass. 10mm Auto :$15.00 per 100 $75.00 per 500 Mixed Head-Stamps May contain both brass and nickel finish.

      Here's the link:
      Diamond K brass:

      10mm Auto :$15.00 per 100 $75.00 per 500
    4. SmokelessPowder
      15 cents a piece isn't cheap. Once fired 9, 40 and even 45 brass costs way less. A used piece of brass shouldn't cost much more than a primer (at least at current primer prices). I've got about 800 10mm cases but I doubt I'll ever get more.
  10. Borg Warner
    Good article. I've been interested in the development of the 10mm since the cartridge was developed, but even more so since I acquired a couple of Glock 20's, a 20C and a 20SF. The Original Norma load for the 10mm Auto produced 1200 FPS with a 200 grain bullet operating at 37,000. But currently most commercial loads for the 10mm list their 200 grain loads at 1050 which seems to be the current industry standard. This is the velocity listed for CCI Blazer (FMJ), Hornady (XTPHP), and PMC (FMJ)

    I suspect that the CCI, PMC, and Hornady ammo is loaded to a lower Maximum pressure than the 37,000 PSI limit of the Norma ammo. I have written to Hornady, CCI, PMC and Hornady asking what Pressure level their ammo was loaded to, and all they would say was that the maximum pressure level for the 10mm auto was 37,000 PSI.

    Buffalo Bore makes a 200 grain load that develops 1200 fps, Double Tap 1275, and Underwood, 1250. My guess is that these specialty ammo companies develop these laods uiasn pressure testing equipment an load their ammo right to the very edge of the pressure limits while CCI, PMC, and Hornady probably stay right at about 35,000.

    While I don't think it would be a good idea for a reloader to try to duplicate the Double tap velocities without pressure testing equipment I know that it's possible to improve over standard factory ballistics using data from Loadbooks USA which has data from all major reloading manuals in one book for one or two calibers only and they publish a book for both the 10mm and 40 S&W. A friend of mine was able to get some impressive velocities using 180 grain XTP's and AA-7 powder using a load that he found in the loadbooks USA manual.

    It's possible to get even more impressive velocities using lighter bullets, but that's really just a trade-off sacrificing mass and sectional density for extra velocity. I think the optimum weight for the 40 caliber is right at 165 grains according to FBI research.
      Overkill338 likes this.