Episode-855- Understanding Caliber, Millimeter, Gauges and Ballistics

The 30-06 is the Father and Grandfather of Many Rounds

The 30-06 is the Father and Grandfather of Many Rounds

When I stated I wanted to do some more shows on firearms topics I was flooded with emails by new shooters that all basically said some version of this…

“Jack can you do a very basics style show that explains what all these calibers and rounds mean.  Sometimes when you are talking about a firearms subject I am fine then you start saying something like the 38 special is 35 caliber and I just don’t get it.  Or that a 40 S&W is equivalent to a 10mm in a carbine.  None of this makes sense, please help.”

Often I feel that those of us who grew up reading gun magazines and shooting our entire lives forget how long it took for us to actually “know what we know”.  My hope today is to condense this stuff into an hour long show in a way that will make sense to newbie.

I also hope that those of you who know this stuff will gain a better understanding of how to explain it to others.  Just because you know something doesn’t mean you know how to teach it.

One thing I can promise you is that even if you are brand new to shooting and ballistics after today you will likely want to pull your hair out the next time you hear some idiot behind the counter at a sporting goods store giving out advice.

Join me today as we discuss…

  • Cartridge vs. case vs. bullets
  • What happens when you pull the trigger
  • Rim fire vs. center fire
  • What is a caliber
  • What is the difference between millimeters and calibers
  • What is a gauge
  • What are some common caliber to millimeter equivalencies
  • What actually does the killing when it comes to a gun shot wound
  • Power mythology – real numbers from real shootings
  • What is “sectional density”
  • What is “ballistic coefficient”
  • How “new” rounds usually come into existent
  • The effects of longer barrels on handgun rounds
  • Choosing a round is not as hard as people try to make it

Additional Resources for Today’s Show

Remember to comment, chime in and tell us your thoughts, this podcast is one man’s opinion, not a lecture or sermon. Also please enter our listener appreciation contest and help spread the word about our show. Also remember you can call in your questions and comments to 866-65-THINK and you might hear yourself on the air.

37 Responses to Episode-855- Understanding Caliber, Millimeter, Gauges and Ballistics

  1. Well done Jack. This is clearing up some things for me (listening right now), and I’ve been shooting all my life. Keep up the great work.

  2. Wow, haven’t even listened to this yet but the description is totally spot-on for anyone who is a beginner or even has a basic understanding of firearms… can’t wait!

  3. John Michaels

    Some of the info you are giving is not factual. Not a major issue unless someone tries to use the information to reload. My understanding is that 9mm is .355″ while 38 spl is .356″ and .357 magnum is .357″ in diameter. I know that if you are using solid lead bullets (even hard cast) having a projectile slightly (one to two thousanth’s) larger is feasible, but if using jacketed bullets, that small difference can cause major issues and damage.


    • Modern Survival

      The tolerances do not matter. First 38 Spc and 357 use the exact same slugs for reloading, they are identical. While 9mm is technically .355 again we are with in .002 tolerance and it doesn’t mean anything. All reloading must be done with proper components and data. The issue with loading a slug designed for 38 Spec or 357 Mag would be far more the overall length or the reduced case capacity (assuming your seated it deeply enough to meet OAL) causing high pressure.

    • Modern Survival

      Additionally many loads use .358 slugs in both 38 and 357.

  4. Thanks for the great show Jack. As you were explaining all I could hear in the back of my head was my father complaining on how we never moved over to the metric system. Shotguns are even crazier, using mass to measure length. Love my Remington 870 18.53mm shotgun.

  5. Val Anderson

    Yes, very good show! I know there is a lot of info to cram into a show –
    one thing I think listeners should know about is the difference between
    .38 Special and +P. I brought my .38 back from Viet Nam (swapped a
    knife for it with a Coast Guarder.) I have shot +P in it (steel wheel) but
    not on a regular basis.

  6. Jack,
    Is the .300 blackout cartridge just a 5.56 cartridge “necked up” and “shortened” to hold a .30 caliber bullet? Also is there a standard rule to figure out if a bullet weight is too heavy for feeding in a magazine-fed firearm?

  7. Jack,
    That was a great summary for people who are just learning about firearms. For those who are interested, here’s three more things that might be helpful:
    1) To convert from caliber to mm, multiply by 25.4. Divide by 25.4 to go from mm to calibre. A .25 becomes 6.35mm. A 9mm becomes a .354.
    2) Survivalblog has a good table of common converstions between caliber and mm here: http://survivalblog.com/2011/06/understanding-metric-and-inch.html
    3) This site: http://www.ballisticsbytheinch.com/index.html shows the effect of barrel length on common calibers.

  8. So as an ex-marine I get most of the time when you talk about firearms. But at tomes you do lose me. This was a really get show. Thank you now I can let the wife and mother in law listen to this and they can understand.

  9. Great show Jack! Now what about Hydrostatic shock as a factor in stopping power? That is the main reason I have been flip-flopping between the .357 Sig and the 40 SW. That and my only real experience is with the Navy issued 9mm. Thanks!

    • Modern Survival

      @CHopper, well if you have shock to internal organs you get disruption of the individuals ability to function.

  10. Your .22 stats fall inline with that school shooting in Ohio. 10 shots fired. 6 students hit. 3 died. 50% death ratio, but sounded like the shooter was very close. Super sad without a doubt, but reenforces .22 as self defense weapon for those who don’t have another option.

  11. Greg Harvey

    Thanks for the informative show. It cleared up a lot of fog for me.
    Quick story on dove hunting. I once shot at a dove and thought I missed but my dad said it just flew into the ground. When we cleaned it, just one pellet had hit it and went through the heart. I thought about that when you talked about how deadly .22’s were. Even a small bullet can get the job done.

  12. This is a great show. I have a friend who has been looking at a carry sidearm for his mom and though she needed bigger but maybe the link to Buckeye will give him some real info, instead of that guy at the gun shop saying a .380 is worthless.
    Mr. Spirko once again you got those gears turning in my brain.

  13. Jack, great show. Do you have a link to the study data you quoted in the show? Found it fascinating, but it went by kind of quickly. Thanks.

    • Modern Survival

      @Nate it is in the notes above man where it says an alternate look at handgun stopping power.

  14. Thank you for a great show. I’ve been shooting since i was a kid and taught Basic Rifle Marksmanship for three years as a Drill Sergeant. I thought I was well educated in weapons till I was playing this show on the way down to my Battle Assembly.

    You explained several things that I had never even thought about as well as many things I “knew” but did not really know. I was able to use some of this new knowledge to help a young Soldier grasp why things are as they are and she qualified for the first time in three years.

    Thanks again for a great show. This is the “caliber” of show we have come to expect from you. 😉

  15. This was just a strait up awesome show. I would and will recommend it to every newbie who has a gun or has interest in reloading. Cleared up a number of things for me even. Thanks for all that you do and the great show.

  16. Great show Jack. I almost didn’t listen to this one because I figured it might be the same as one of your older shows on this topic. Man, I’m glad I did. Turned out to be a very interesting show that I will probably listen to again.

  17. One thing to remember is a pistol is designed to stop and a rifle is designed to kill. All in all great show.

    • Modern Survival

      @Adam that really isn’t the case at all. A pistol is designed to do what it can within its limitations. It is also designed as a killing tool, saying otherwise leads to some dangerous conclusions.

  18. I may have missed it, but you were going to talk about the difference between a clip and a magazine. Did you? I do need to listen to this again. Thanks for the great information.

    • here’s a great explanation:

      (kind of complicated!)

    • Jack skipped defining the difference..

      • Modern Survival

        @Insidious, yep and likely because I don’t really care. I don’t care if you call a mag a clip or vise verse, I care if you can shoot and run your weapon. This is one of those areas where it is mostly about people who are poor shots or operators trying to make themselves sound smart because they can’t shoot. This is an area where arm chair ass cracks run their beaks on youtube about people that do while they do noting except critique others on a technicality that doesn’t matter.

        Please don’t take this personally I know you are not like those I describe above.

        • no offense taken at all

          I was always confused about what a clip was when I read WWII history as a kid (‘..we were down to 2 clips per man..’) and didn’t know myself. So i asked my friend google.

          I’m sure knowing this little bit of trivia will have absolutely no effect on my gun handling skills.. =)

  19. Thanks for this show. In my opinion, from my level of knowledge, this was one of the most useful shows. How about a “level2” and “level3” show? I’d also be really interested in big picture briefing on gun laws. In my case, I wasn’t aware that there is a federal law limiting gun rights within 1000 feet of a school. I live within 1000 feet of a school. I can easily comply with this law now that I understand it, because I stumbled on it (luckily while researching my first gun buy -so I was never in violation) but I guess my concern is that I don’t know what else I may not know if that makes sense, and I intend to comply with the law 100percent. I understand you can’t give legal advice or know the ins and outs on every state law…but possibly a “be aware of this” or ” look into this for your state” level show. Thanks for all your work.

    • Modern Survival

      @Ace, I will see what I can do on a level 2 or 3 style show but I likely won’t touch the legal stuff. Too much variation so what I say in one place my protect you and get you locked up in another.

  20. Anyone ever watch “Swamp People” on The History Channel? Anyone ever notice that the VAST majority of the alligators are taken with a .22LR or a .22 magnum? Sure the “sweet spot” is the size of a quarter and they are trying to shoot it from inches to maybe a foot away, but it gets the job done. I think shot placement is way more important. I don’t want to be shot with anything, but I’ll take a .45ACP in the arm or leg over a .22LR through the eyeball any day.

  21. Jack,

    I noted a minor distinction in this show as I was listening today. Caliber does not refer to only sizes as a measurement of a fraction of an inch. I remember from my trips to the USS North Carolina as a kid that the secondary armament (5″ guns) was 38 caliber. Not .38, 38. So I fired up wikipedia and found:

    BB-55 USS North Carolina armament

    9 × 16 in (410 mm)/45 caliber Mark 6 guns
    20 × 5 in (130 mm)/38 caliber dual-purpose guns

    I asked a veteran about the measurement but alas I cannot recall his explanation. It was only 30 years ago. Anyway, caliber can be more than .38 or .45 but you gotta have Uncle Sugar buying your ammo.

    • wikipedia says:

      In some contexts, e.g. guns aboard a warship, “caliber” is used to describe the barrel length as multiples of the bore diameter. A “5-inch 50 caliber” gun has a bore diameter of 5 inches (127 mm) and a barrel length of 50 times 5 inches = 250 inches (6.35 m).

  22. Dexter Sensui

    How do you compare AK-47 to the M-1 and why is the AK seem so popular weapon?

  23. Pingback: All About Guns (Part 1) |

  24. Pingback: Heels and Handguns » Stopping Power: Do You Really Need a Large Caliber?