KABOOM: The .223 WSSM and 6mmBR Disaster

6mmBR (left) and .223 WSSM (right) cartridges above the remains of Browning A-Bolt rifle.

This post was written by Dr. Jim and Mary Clary.

Under most circumstances, shooters don’t have to worry about chambering the wrong cartridge into the wrong rifle. After all, the cartridges are well marked and we all know which rifle we are shooting on any given day. In many cases, incorrect cartridges cannot be chambered–larger cases will not fit in smaller chambers, for example. No problem! That being said, I can tell you that even an experienced, careful and normally safe shooter can make a mistake.

The following is an account of just such a mistake that could have resulted in death or dismemberment. Fortunately, the shooter was not hurt, but the rifle was completely destroyed.

Last year, a friend purchased a Savage Precision right bolt, left port, single shot bolt action in 6mmBR Norma. It was an incredible prairie dog gun and he spent the summer burning powder and busting dogs. In October, he purchased a stainless steel Browning A-Bolt Varmint in .223 WSSM. The weather in the upper Midwest turned sour by the time he got the brass tuned up and he only got to fire it a few times before he was “socked in” for the winter. Thus, he spent his evenings loading ammo for the spring thaw.

During a break in the weather, he grabbed both rifles and a couple of bags of .223 WSSM and 6mmBR cartridges and headed to the range to check out his new loads. In case you are not familiar, the 6mmBR is smaller in diameter and a mite shorter than the .223 WSSM. Because of this, it will chamber in a .223 WSSM, but the .24 caliber bullet is too big for the .22 caliber bore. That is what happened to my friend.

The rest is history; when he squeezed the trigger, all hell broke loose. The entire bottom of the rifle blew out, including the magazine assembly. The explosion actually cut the stock into two pieces. However, the bolt held and amazing as it may seem, the .243 bullet was “swaged” right out of the .223 barrel.

Now, realize that my friend has been shooting all manner of firearms, safely, for over half a century. He is meticulous, thorough and conscientious in his approach to reloading and shooting. However, he made one mistake. He put some loose 6BR cartridges in a baggie as he packed up from a prairie dog hunt last summer, without noticing that the baggie was marked .223 WSSM in black marker. Then, when the break in his winter weather came, he grabbed the bag, believing it to be the WSSM cartridges and didn’t check the head stamp.

Couldn’t happen to you? How many times have we emptied our pockets of cartridges and dropped them into a plastic container on the shooting bench? How many times have we set down to a marathon reloading session, loading several calibers in a row? How many times have we put the wrong bullets, cases or primers into the incorrect container? My point is that even the safest of us can make a mistake. So, look at the picture above and take a bit more time when you reload your ammunition at home or chamber a round in the field. It might save your life.

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Datum Line

    Only wildcatters can save wildcattters. Or Hold my headspace watch this.

  • Alex

    Don’t worry, that will buff right out.

  • Ben Giselbach

    It would be easy to get .380ACP and 9mm confused if they were both in my pocket, and I reached down to grab them and forgot I had two different kinds of rounds in there. While a 9mm Parabelum wouldn’t fit in a .380ACP chamber, the .380 would fit in a 9mm. Though it probably wouldn’t destroy the gun (the 2mm gap left by the brass might hurt the chamber/rifling intersection though).

    • JumpIf NotZero

      I’ve had .380 wind up in a 9mm chamber, hasn’t ever fired for me.

    • Hunter57dor

      so there is your first problem:

      if you have loose ammo in your pocket, check the bloody headstamp before doing anything with it.

    • dragon5126

      you will know when you load the magazine…

  • gunslinger

    hope your friend is ok

  • allannon

    This is oone of the reasons I consciously avoid dimensionally similar cartridges. I just know this would happen to me.

    • Cornelius Carroll

      +1 :/

    • It could happen to anyone—

      • Ivan Relppa


      • allannon

        Oh, indeed. That’s why I try and minimize the chances. Murphy and I have a long and–for me–unfortunate history.

        For example, dad once put naptha in a can marked “gas for mower only”…

    • dan citizen

      I am a heavy user of 12 gauge. So I will not own a 20 gauge, largely for fear of a potential mix up.

      • allannon

        12ga is dimensionally different enough I can readily tell it from 20 (I shoot both).

        But I avoid, say, 5.56x45mm and x39mm. 😉

        • El Duderino

          The problem is that the 20g will drop and get stuck in the barrel. In the field it’s plenty easy to mix up when you’re paying attention to the birds, the retriever, your buddy’s kid, etc. The next shot with a 12g and it’s time for a new face…

          • allannon

            I’m aware of the potential issues. I have been shooting both gauges for a couple of decades now.

            I have never found them easy to mix up, even with quickly grabbing a shell to try and get a bird before it’s out of range. 12ga is wider and heavier; as soon as you grab it, even if you don’t notice the difference in diameter, the weight is a huge indicator that you’ve got the wrong type. 12ga and 20ga have a 7/64″ difference in diameter and 230 grains difference just in shot.

            It’s not like mixing up .308 and .243, which unless you happen to note the bullet are very nearly. Even the mentioned 6mmBR and .223WSSM are within about 4/64″ of each other, and the differences in weight, unlike a shotshell, are a matter of maybe a tenth of an ounce, not a whole half-ounce.

          • AR_Libertarian

            I have both .308 and 7mm-08. I guess I’d better be extra cautious.

          • dragon5126

            I havent used it in decades so I dont know if its still available, but back when I used to shoot both 300 win mag an 7mm rem mag I used to mark the 7mm with Brass Black it works just like cold blue just mark the heads and you are good to go OR get a good BRIGHT nail lacquer (ask the lady which holds the best) and seal your primers with it, AND USE contrasting colors and coat most of the head for visibility

            EDIT Just checked Birchwood Casey still makes the brass black… with today’s epa, I wasnt sure…

          • dragon5126

            there once was an industry effort to color code the hulls of shotgun shells but as the saying goes, “the best laid plans of mice and men”…

        • dragon5126

          the 5.45×39 and 5.56×45 are different enough as well I just dont see the worth in having two firearms so close together in ballistics…

  • Paul O.

    Accidentally fired a 32ACP in a .380. Didn’t cycle the gun and accuracy wasn’t too great. Now I don’t even take the guns together to the range.

  • Ian

    Friends don’t let friends use silly wildcat cartridges.

  • Tim Pearce

    Actually, you’d be surprised how many shooters do not know that their gun shoots one, and only one, kind of ammunition. So many think a .38 is a .38, whether it’s .38 Special, .38 Super +P or .38 S&W

    • RoCr

      The problem is that there are exceptions. Quite a few, really. A firearm chambered in .357 magnum will chamber and fire .38 Special without a problem; same with .44 magnum and .44 Special; .410 bore and .45 LC; .460 S&W can chamber .454 Casull, .45 Colt and .45 Schofield, etc.

      • dragon5126

        BUT REMEMBER chambering and safely FIRING are not the same thing… for example the .410 and .45 Colt… WHO’S 45 Colt??? there are some out there that will blow a .410 barrel apart, such as the corbon loads that are not even safe in some true .45 colt revolvers… the same for some of the Buffalo Bore Loads…

  • Joseph B Campbell


  • JumpIf NotZero

    This is pretty much the the one remaining issue keeping me from owning a 300blk gun.

    It’s just so easy for a friend, a kid, a stranger to accidentally pop a 223 round in a 300blk mag. Even if you mark mags specifically with caliber, you use only FDE or OD mags for 300blk, you only bring that one round to the range… Sometime, somewhere, someone will get it mixed up.

    I’ve seen this happen once, heard a second hand report from a friend, and seen it a few times on the Internet.

    It doesn’t even have to be 223 dropped in a 300blk chamber, it could be a 300blk forced into a 223 chamber. Both are exceptionally bad.

    • CrankyFool

      I’m curious — what would happen if you dropped a 223 round in a 300blk mag? If it sat solid enough to take a primer hit, it still looks like the projectile would practically fall off the tip of the barrel — there’d be no rifling engagement, and no containment of gasses by the bullet. You’d possibly get a fun little fireball effect, but I’m not seeing the catastrophe here.

      (Asking because I’m certainly enough of a neophyte to have missed something)

      • JumpIf NotZero

        A 556 “shouldn’t” fit in a 300blk chamber. I suppose with a good force or shitty brass or some dumb luck with the floating firing pin would make for a bad bad day.

        Supersonic 300blk will drop right into a 300blk chamber however. Bad joojoo.

        • Hunter57dor

          say again?

          its supposed to be completely interchangable, no change in pressure between sub and supersonic.

          at least thats what they claim. don’t own one myself.

          • JumpIf NotZero

            300blk super and sub are (for the most part) interchangeable. But you CAN fit a supersonic 300blk round into a 556 gun… the result is BAD. They are about the same size, take the same mags and parts… It’s probably the easiest cartridge to mix up that I can think of offhand, needs extra attention if you own both.

          • dragon5126

            no you can not. it will not chamber

          • dragon5126

            dont worry he’s mistaken

        • HSR47

          For calibers like .300 blk and .45 ACP, supersonic loads generate the same pressures as subsonic loads, they just use lighter projectiles.

        • dragon5126

          “Supersonic 300blk will drop right into a 300blk chamber however. Bad joojoo”
          Incorrect! Good MOJO! this is by design. the 300blk was designed as a dual purpose round, subsonic for use with a suppressor installed and supersonic with it removed, so that both rounds can be fired in the same firearm.

      • A Mericano

        Nothing spectacular would happen if you managed to force 5.56mm into a .300 BLK chamber. It would fire, the bullet would probably be “bumped up” to .30 and you would have to manually extract the weird over-long .300 BLK case that had just been fireformed.

        People have fired .243 Win in .308 Win chambers, .25-06 in .30.06 chambers and so forth for years. Usually accidentally, sometimes out of ignorance.

        Where one runs into problems is when the cartridge being chambered is shorter but has a larger diameter bullet. 8mm Mauser has wrecked more than one .30-06 rifle.

        If you manage to force a .300 BLK into a 5.56mm chamber? Then you deserve whatever bad thing happens to you and your rifle.

        • JumpIf NotZero

          260, 243 , etc are all 308 cases. They are support Ed in the majority of the area, and all have the same OAL.

          556 in a 300 would stick out unless forced in. If forced in enough to strike, it would almost certain be out of battery. Kaboom.

          You can’t compare to smaller 308 based cases. Because you’re right those will just tumble out recklessly with no issue, but they are in battery none the less.

          • dragon5126

            actually No they Dont all have the same OAL similar but not the same. the 260 is longer than a 243… Just because they are based on the same cartridge does not give them the same length the narrower projectile will yield shorter brass, bullet seating depth will change length and case pressure, both are variables determined by bullet weight which is a function of bullet length there are maximum and minimum OAL that are in the picture as well… ALSO an AR, unless damaged will not fire out of battery

        • dragon5126

          amen on forcing a 300 into a 556

      • dragon5126

        First off the most likely thing to happen (noted from experience by trying) is a failure to feed, Due to the smaller round, in the wider magazine lips the 5.56 nose dives in the magazine and doesnt go anywhere. In other instances it hits high above the chamber resulting in a jam. If it DOES get forced into the chamber and the bolt does lock closed the case will either expand or rupture depending on the brass, IF the firing pin can get a solid hit There are man variables involved, including the phase of the moon and which wednesday of the week is closest…

    • dragon5126

      Dont know where this one came from, I have them both and it just wont happen, check the measurements on them including head size, effectively the 300 is just a straight walled 7.62×39… the 5.56 wont be fired by a 300blk bolt as it wont hit since it wont be held in place it will be deeper in the chamber due to neck ,throat and bore differences and the 300blk wont chamber and allow the bolt to go into battery. Ive tested it personally

      • JumpIf NotZero

        Ok, well, it’s happened so…

  • CrankyFool

    What happened here seems to have required TWO issues to occur:
    1. You have two weapons with exceedingly similar ammunition; and
    2. You’re not completely anal-retentive about separating out the ammunition.

    How many times have I emptied out my pockets of ammo? lots. But this is one of the reasons why I don’t even have both 9mm and 40S&W weapons in the house — because you have to either do your due diligence ahead of time by trying to avoid dimensionally-similar-yet-deadly-different ammunition from coming into the house, or trying to avoid mixing it after it’s in the house.

    Thankfully the guy is alright. I worry that the lesson here seems to be “well, shit happens.” Shit doesn’t happen. There are no accidental discharges. The “accident” above was a case of negligence. I really hope he — and ideally all of us — learn something from this.

    • dragon5126

      on the 9mm/40 S&W, there is no issue the round size is substantially different. 9mm is .355 and the .40 is a true .40. In most cases the 9mm literally pop out of a .40s magazine when pressure is put on the spring, and the .40 will have an issue being inserted into a 9mm mag, I have done this personally to prove this very point, as I do own and shoot both. The only problem comes when you own the same ake firearm such as a Beretta 92 AND a Beretta 96 where other than markings and bore diameter, they look identical, (same gun except the 96 is a .40 S&W), in which case it is possible to mix up magazines, loaded or empty…

  • james

    My brother put a few .40s thru a .45 1911 and only noticed because the recoil was different. Damn thing cycled and fired just fine. No more loose ammo in bags from then on. Even in commercially loaded ammo I’ve found weird stuff like no primers or once a totally different caliber round! (Again a 40 in with 45) Just gotta be really careful all the time and remember that you’re dealing with potentially deadly consequences if you mess up.

    • Hunter57dor

      how on earth did you load the magazines?

      .40 is so much thinner, it would just go right past the feed lips.

    • Torn

      Recently found 3 rds of 9mm, no primer and NO flash hole

  • Mark

    I once asked for a box of .45 acp at the range and got a box of .40s. I noticed when they fit weirdly in the magazine.The range guy felt so bad be gave me an extra free box of .45s. That said, I have to admit that I still don’t always remember to check the writing on the box — though I try to.

  • Lance

    Ohh STEVE quit blowing guns up they look cool but its such a waste of good weapons!!! LOL

  • Kyle

    I have to agree with a few people, this wasn’t an accident. An accident can be prevented, but this was just being lazy and not inspecting your ammunition before you load it into your gun.

    • Realistically though most people don’t inspect the caliber of every round they’re using. You go to the range and shoot two similar size calibers and accidentally place a 40 in a 45 box. Next time you just load up. I can see that happening to almost anyone.

      • Chris Spicer

        I inspect every round. You can take the boy out of the Infantry, but you can’t take the Infantry out of the boy.

        On a related note, the phrase, “complacency kills” is one I teach every high angle rescue student. Fits this shooter’s situation, I believe.

      • Kyle

        When you own two exceedingly similar rounds, I would imagine you would take extra precautions that this doesn’t happen. When I shoot at the range, I shoot one gun at a time, and only bring up one caliber to the bench for each gun so this sort of thing does not happen. It’s not inspecting the caliber of every round shot, because I’m not a numbskull and just throw my two similar rounds into a bag and expect mistakes not to be made. This guy got complacent and lazy, and this is what happens when you get complacent and lazy.

      • dragon5126

        yes it can happen, but bottom line, it is the result of negligence. there are as many “RULE NUMBER 1’s” as there are calibers, and one of them is ALWAYS check your caliber when loading your firearms. I own over 100 firearms, are they all the same caliber? NO. I have converted a pantry into an ammo locker every place is boldly marked, and STILL I HAVE to double and triple check calibers, there are NO accidents with firearms. only negligent actions.

  • Leoon

    what happened to the person holding the rifle? I mean what happend to his hand?

  • Cuban Pete

    Attention to detail will never hurt you.

  • Hunter57dor

    seems like a pretty rookie mistake.
    i have not been reloading long, but i am absolutely meticulous about everything that goes in my firearms. don’t mix the brass, don’t mix the ammo, make sure you know what powder you are putting in, and how much, etc.

    any less, is just being foolish with the one life you have.

    • dragon5126

      it is because you are still at the “I might make a mistake” stage that you are safe. people with YEARS of experience and develop habits are at the greatest risk of stupid mistakes when reloading. I used to reload for our test chamber. One day the big boss came in and had a fit because he saw what he perceived as me skipping the visual inspection of all the powder filled cases at once, comparing them, to ensure none had a double charge, It took nearly 2 hours to settle him down enough to explain that the low pressure loads we used in the chamber, developed with shotgun powders, cold NOT be double loaded, Even if we FILLED the cases with powder they would be well below maximum, and were only loaded to the low end to prove function, anything that required more than that we tested with factory loads at the range. Each round for the chamber was done one at a time to ensure the load stayed in the low pressure range FOR safety to prevent blowback and noise and lead powdering. There are so many issues we face when reloading it becomes very easy to lose track of some of them. in the instance of our test loads, the load data came from the test chamber’s mfg’s safety sheets to limit lead exposure, and reduce risk of detonation. it also resulted in a type of unburnt powder residue that was easier to clean out to to “fluffyness”

  • Darrell

    I took my K31 (7.5×55) to the range one day years ago, along with one of my Swede Mausers (6.5×55). I was shooting Prvi in both guns that day, the ammo boxes looked identical. At one point I tried reloading and shooting the Swede, and discovered that the rounds would not chamber. Inspection revealed that I’d put the K31’s ammo in the M96. It wouldn’t fit, of course, no problem there. I’ve always wondered what might have happened if I had loaded the Swede’s ammo in the Swiss rifle…

  • big daddy

    My days of any not attention to detail mistakes are over. I have become very what slobs and losers call anal retentive in my old age. I have seen people cut fingers off working with power tools and toes off with lawn mowers. When I work with anything that can injure or kill I am detail oriented to a fault.

    I remember my now ex-wife handing me an electric cordless drill with the bit pointed at my head. I almost lost an eye. From then on I always look at what someone is handing me. I never let someone’s carelessness negatively effect the outcome of what I am doing now. I certainly won’t let my own do so at any cost.

    The idea that firearms are more likely to kill than injure by nature my attention to detail is above any other endeavor. With weapons of any kind there is no such thing as too careful. Constant inspection is your friend and should become a habit to the point of being obsessive compulsive.

    It’s a mistake anyone can do but a mistake that should NEVER happen.

  • Laserbait

    I thought I read this before – http://www.chuckhawks.com/223_6mmBR_disaster.htm

    • Julio

      Me too. Thanks for finding it.

  • Julio

    “a couple of bags of .223 WSSM and 6mmBR cartridges”

    “Bags”? Seriously?

    As someone once said: “Now that’s your first mistake, right there.”

    Keep your ammo in properly marked boxes and put the fired cases back in the empty holes afterwards. It prevents damage and lets you keep track of both loaded and fired cases.

    This once saved me from making a big mistake even worse. Thinking I’d already cleared it, I’d failed to check a rifle before putting it in its slip and stowing it in the back of the car. But when I went to put the rounds from the magazine, and the empty cases from my stock pack, back I noticed that one was missing. After checking my pockets, it dawned on me where the missing round was: still in the chamber.

    As a friend said to me at the time: “you’re only as safe as the last thing you do”.

    Nothing bad happened, but it so easily could have done. and if I’m sharing this shameful tale, it’s because I don’t want anyone else to make the same mistake, not to brag about how I got away with it.

    • dragon5126

      Sadly ctg case mfgs price things in a manner that causes people to try to save money in what they see as an “optional item”. When I do loads for “battle rifles” I do up battle packs, stripper clips and heat sealed bags. WHY? they are used in drills, every part including reloading magazines is a time based issue. THAT IS THE ONLY TIME that rounds are NOT put into boxes that separate each round into its own little division. I also have learned to make plexi and lucite boxes (covers) for wood blocks, hard pack styrofoam and plastic blocks that can be drilled to hold precise numbers of rounds. screws for hinges and dimples to snap onto keep the lids closed, heat bends the lids it is easy to do and can be relatively cheap. the benefit of the clear cover is seeing the number of rounds at all times and getting in the habit of case head up loaded, open mouth up fired also makes the at a glance verification fast.

      And that ISNT a shameful tale, too may things going on at once cause things like this all the time. and we ALL have been rushed off the line so that the range can maximize profit and the range master forgot the cardinal rule about safety first

  • Aaron E

    We used to use Glock 22 in .40 S&W, and 9mm MP-5’s. Thankfully the only issue we had was the rare “light” shot from the .40 shooting a 9mm. It could be done from a Glock 22, but was always followed by a failure to eject. To my recollection we never had the .40 jamming the 9mm.

    That was one of the reasons we switched to an AR-15 platform – to completely separate ammunition types. That and HK really dropped the ball with training, armorer schools, and in some cases service.

  • politicallyincorrectshooter

    IIRC Hatcher demonstrated that lead core bullets would swage down without problems if the case itself did not fail. Even .35 down to .30

    • dragon5126

      that was with lower pressure ctgs.

  • Wes

    Always cool to see a safety system work exactly as designed. Gas went right out the bolt gas vent and down the magazine box. Glad shooter is OK.

  • Alan Aardman

    One of my old shooting buddies once took a box of .40 S&W that was lying around and announced that he was going to shoot it with his 9mm CZ P01. He then lined up three .40 cartridges on the target stand and plinked them off, one by one, with the P01, at 15 yards.

    • dragon5126

      bad joke very bad joke

  • dragon5126

    Back “in the day”, when we were smithing, an older couple brought in their prized SW Model 27 Target Masterpiece,with a solidly lead filled bore. They both shot the same gun on a league, and purchased all lead (no gas checks) 38 spl wad cutters from the range. Between the light loads and the weight of the gun the gentleman didnt notice the lack of recoil from six squib (REAL LIGHT LOADS) loads, and bifocals kept him from noticing no holes in the target until it was retrieved. They found the issue first when his wife went to dump his brass and the last round just jumped the cylinder gap and no more, locking the cylinder in place. KNOW Your rounds, examine them, look at them, shake them, dont blindly trust them… had any one of these rounds been up to par there is no telling what the result would have been.
    Fortunately a quick examination with a machinist’s probe confirmed all cylinders were fired and we were able to disassemble the revolver and slowly and evenly heat the frame and cylinder with a torch set to a neutral flame so as not to harm the blueing or affect the metal in a negative way, until the slugs melted and flowed out the barrel. When cooled we did a routine deleading and fired 20 rounds of copper jacketed through it to confirm that it wasnt damaged by the misadventure. In the time spent gunsmithing this is just one of the ammo specific problems we ran across at the shop, out of countless numbers including one case of an individual reloading .22 HP with the wrong powder AND load, which destroyed a factory original condition Savage 1899 and resulted in the shooters death. The firearm came to us through the insurance company for appraisal for the widow’s benefits along with the handloads he had “worked up” to determine if they warranted further attention… Somedays you really Shouldnt get out of bed because being truthful really sucks.