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Thread: Shooting 40 S&W in a 10mm Semi Auto?

  1. #1
    Boolit Master am44mag's Avatar
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    Shooting 40 S&W in a 10mm Semi Auto?

    I'm curious as to what you guys think of this. I've been hearing about people doing it more and more, but haven't really heard of any serious mishaps happening because of it. I believe the logic behind doing it is that the extractor will hold the case against the breech, so the round will headspace off of it instead of the case mouth (it also allows the firing pin to actually reach the primer).

    I'm not suggesting anyone do this, or that it's safe, but beyond the blanket statement of "only shoot what cartridge your gun is chambered for", what are the possible dangers to doing this?

    And before anyone asks, no. I do not plan on doing this regardless of whether it's safe or not. I do not own a 40 S&W, and 10mm brass is pretty inexpensive as it is, so there would be no benefit to me doing it. I'm just curious about it.
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    Aaron

  2. #2
    Boolit Master


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    I saw a man shooting 45 Gap in a 45 ACP back in the middle of the Obama ammo scare. It was what was available to them and it did work. Seems like it would not be good for yous extractors longevity though.
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  3. #3
    Boolit Master

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    Yes, it works and the .40 headspace off the extractor. .40 brass is free and 10mm isn't

  4. #4
    Boolit Master

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    In these situations the extractor holds the case so the firing pin can hit the primer. The case is not headspacing on anything really....if the extractor is worn ...the gun wont fire.
    Shooting rounds that are similar , in guns not chambered for them will probably lead to a broken or damaged extractor.
    It happens a lot, 9mm Luger shot in 9mm Largo , 380 in 9mm Luger , 9mm luger in 38 Super, the list goes on . Again if the rounds are similar like , 40 S&W and 10 Auto , the danger would probably be more to the gun than the shooter.
    But why take the chance of damaging a good pistol. In an emergency situation...maybe but as a rule just reload a lighter 10mm Auto round , buy another barrel or buy a 40 S&W ...too many better options than shooting the wrong ammo in a pistol and risk damage to it .
    Gary
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  5. #5
    Boolit Grand Master Texas by God's Avatar
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    My brother recently bought a long slide Glock 10 mm. We shot one box of 40 Smith & Wesson through it and it was a non-event. Perfect function, fired brass looked normal, and accuracy was okay. We filed this under "emergency knowledge."The case heads are identical so I'm not sure how the extractor could be damaged. I have seen heavy crimped .45 ACP that in no way they could headspace on the chamber mouth but yet they worked fine. I suspect the .45 GAP will too but unless someone gives me some I'll not do it.

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  6. #6
    Boolit Grand Master
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    Accuracy may be less than stellar with the bullet skipping off the chamber shoulder on its way downbore. Leading with cast is likely to be more pronounced. There is increased free travel for gasses to escape past the bullet on its way down the chamber that is too long for it.

  7. #7
    Boolit Grand Master

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    One other issue that may come up is the same as 38 spl in 357 and 44 spl in 44 mag. you may develop a carbon fouling ring in the longer chamber causing problems when the longer case is used. Normally the extractor is there and the case mouth cushions the pins blow. In this the firing pin is going to be taking the hit on its face from the firing pins hit. Probably not a big thing but not the way it was meant to work.

  8. #8
    Boolit Buddy KVO's Avatar
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    If one were truly set on using 40 S&W brass in a 10mm auto, the best approach would be to load rounds long and set up to headspace off of the boolit engaging the rifling leade. i.e. when rounds drop in the chamber for a "plunk test" the case rim should be flush with the barrel hood as target 45 ACP loads are traditionally set up. My personal vote would still be to buy 10mm brass, it's cheap enough.

  9. #9
    Boolit Grand Master
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    Given the difference in length between the two rounds I am not sure that is possible with many bullets while still allowing sufficient case grip on what little of the bullet remains in the case.

  10. #10
    Boolit Master

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    One possible scenario:
    1. Take 10mm auto pistol and load magazine with 40 S&W ammo.
    2. Insert magazine and rack slide
    3. Pull trigger and hear "click"
    4. Grunt in disgust, slap bottom of magazine to fully seat it, and rack slide again.
    5. Have nose of round from magazine impact the first cartridge's primer. First cartridge wasn't held by the extractor, it was instead driven deep into the chamber, where the firing pin couldn't reach it.
    6. Primer goes off from impact. Powder in first cartridge ignites. First cartridge fires in a totally unlocked and out of battery pistol.
    7. Life suddenly gets interesting.
    Remember: Ammo will get you through times of no money better than money will get you through times of no ammo.

  11. #11
    Boolit Master
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    I bought a 40 barrel for my 10mm Glock and had DougGuy throat it to accept a round with the bullet seated out to 10mm length. I can load to pretty much full 10mm power but use 40 brass that is basically free.
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  12. #12
    Boolit Grand Master
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    Sounds like a candidate for 180s and 200s.

  13. #13
    Boolit Master
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    The dummy rounds I sent him to fit it for were loaded with the NOE 200 grain WFN bullets.
    NRA Endowment Member

    Armed people don't march into gas chambers.

  14. #14
    Boolit Grand Master
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    That’s verging on too much bullet for a standard length 40, certainly.

  15. #15
    Boolit Master

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    Personally I wouldn't do it, but I've heard and seen enough people doing it without problem to admit that clearly it is feasible.

    This might be another of those things where you have people like myself on one side saying don't do it, sounds like a bad idea; and others on the other side that do it all the time without trouble.

    I don't currently own a 10mm, but I guess it's a good thing to know in a pinch.

  16. #16
    Boolit Master
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    Well you can always use 10 mm brass and load lighter....Same with a .357. You don't need full power loads when fooling around..

  17. #17
    Boolit Bub cas's Avatar
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    Unfortunately the website is gone now, but there was a page with several photos of bad things that can happen (from a couple different guns). Hammered case heads, cases where the unsupported (lack of headspacing) allowed the primers to back out, then the cases traveled rearward and smooshed smashed the primers in all ugly ways and directions. Hairy stuff.

    I suppose how dangerous it is really depends on your extractor and how tight to the breech face i holds the case. Some guns yes, some guns no. None for me thanks.
    Former cylindersmith.

  18. #18
    Boolit Master

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    On a similar note, I was sorting some range brass recently and found a .380 that looked really ugly. The fired primer was seriously and dramatically flattened. I couldn't understand what could have happened to it. On closer look it seemed clear that it had been fired in a 9mm. My assumption is that the primer had backed out, then pushed back in and crushed badly as the pressure forced the case back. I don't know that any harm was done but it sure looked bad.

    I do recall that I was told by one person that .40 ammo in a 10mm worked best in a Glock, because of the extractor. I don't remember the specifics. My BIL has a Glock 10mm, but he doesn't shoot it much and I've been collecting 10mm brass for him as I find it here and there.

  19. #19
    Boolit Master am44mag's Avatar
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    Quote Originally Posted by 376Steyr View Post
    One possible scenario:
    1. Take 10mm auto pistol and load magazine with 40 S&W ammo.
    2. Insert magazine and rack slide
    3. Pull trigger and hear "click"
    4. Grunt in disgust, slap bottom of magazine to fully seat it, and rack slide again.
    5. Have nose of round from magazine impact the first cartridge's primer. First cartridge wasn't held by the extractor, it was instead driven deep into the chamber, where the firing pin couldn't reach it.
    6. Primer goes off from impact. Powder in first cartridge ignites. First cartridge fires in a totally unlocked and out of battery pistol.
    7. Life suddenly gets interesting.
    Possible, but probably unlikely. The same thing could happen in any semi auto if you have a round that failed to extract and a new round tried to chamber. Flat nose bullets would likely make this a non issue as well.

    Quote Originally Posted by CLAYPOOL View Post
    Well you can always use 10 mm brass and load lighter....Same with a .357. You don't need full power loads when fooling around..
    I believe the reasoning for doing this isn't just to have a lighter shooting round. Truth be told, most factory 10mm is anemic compared to what it is capable of doing. The main reasons I've heard for doing this is to save money, or because of the availability of 10mm ammo.

    One of my favorite loads to shoot is a super light 10mm. I'm getting about 966 FPS out of a 4.5" barrel with a 180gr boolit. I also modified the gun (XDm) with a 22lb recoil spring since it would chuck brass from hot 10mm loadings into the next state. The ammo still cycles the gun, and the brass falls about 2-3 feet away. Recoil is negligible.
    ______________________________________________
    Aaron

  20. #20
    Boolit Master
    contender1's Avatar
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    Generally speaking, to answer the question; "Can it be done?" Short answer, "Yes, most likely."

    The long answer is that it should be discouraged unless it's an emergency & a potential life or death issue.
    Why?
    Physics & how a gun is built & designed to work.
    The basic difference in the 2 calibers in question is the OAL of the case, followed by the available power in the larger capacity case. Much as the 38 spl vs. the 357. Generally speaking, almost any firearm made to accept a 10mm will be able to handle the lower power of the 40 S&W. But,, looking at the physics of a rimless case, vs a rimmed one, and how each firearm is built makes one pause to consider the differences.
    In general, they both are DESIGNED to headspace off the case mouth, whereas the 38/357 use the rimmed case to determine the headspace. The 40 S&W will not have the same support in a 10mm bbl, as the 10mm case will, while the 38/357 both receive the same support.

    Sadly in todays world of so called "experts" we see all kinds of things done that should never be attempted. ("I drive better after a few drinks." "Sure it will work, I do it all the time." "I just load the powder in the case until the bullet compresses it a little, and never weigh any powder." "Reloading manuals are just a guide, I can load my stuff 10%-20% higher & I've never had a problem." And many, many other things we all know should not be attempted.)

    Can it be done? Yes. Should it be done? Not necessarily.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check