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What's wrong with releasing the slide on an empty chamber?

Discussion in 'Handguns: General Discussion' started by mellow, Dec 27, 2002.

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  1. mellow

    mellow Member

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    I know it has something to do with guns that have trigger jobs. I have a Les Baer TRS and a Wilson KZ-45.

    The reason I'm asking is because I have a couple dummy rounds that I can't disassemble with my intertia bullet puller. These rounds have no powder inside nor do they have a primer. I was thinking about using them as practice rounds, but wasn't sure if it's safe to slam the slide closed on them. The only reason why I see this might not be able to be done with my "dummy" round is that it has nothing there to substitute the primer.

    Is it safe?
     
  2. Mal H

    Mal H Administrator

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    It's perfectly "safe", but it is not good for the pistol. Most pistols are designed to strip a cartridge from the mag as it slams shut. Having a cartridge in the chamber puts undue stress on the extractor. Probably won't break immediately, but that is the right thing to do if you want it to break eventually. OTOH, having the brass absorb some of the shock is good for the slide, but the extractor problem outweighs that point. Also, you really won't have the equivalent of snapcaps if that is your reason for the dummy rounds. Snapcaps are designed to prevent damage to the firing pin, and the dummies won't do that.

    Oh, and I'll move this to Handguns.
     
  3. Navy joe

    Navy joe Member

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    Mal covered what's wrong with what you are doing. In your situation let the dummies feed from the mag and dryfire away, I haven't hurt a 1911 pin yet by firing without a snapcap. Dropping the round in the chamber and then dropping the slide is definitely bad for your extractor. Maybe not so much as with your KZ-45, but still not the best plan.

    For what you asked about an *empty* chamber; the reason is releasing the slide on an empty gun that's not stripping a round from the mag lets the slide slam into battery with considerable force. On guns with nice triggers the jar can damage sear to hammer mating surfaces. When dropping the slide on an empty gun, ride it forward.
     
  4. mellow

    mellow Member

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    IIRC, it doesn't matter how many times I dryfire my 1911 and glocks, so it wouldn't make a difference whether or not I have a primer substitute there, right??

    I'm wanting to use these "dummy rounds" less for dry fire practice, more for magazine reloading practice. I would be closing the slide with the magazine in, loaded with the dummy round.

    Mal, I'm not sure if I understand your post. It's unsafe to close the slide on my "dummy round" because it'll put undue stress on the extractor?

    What's the reason behind the rule that you're not suppose to close your slide on an empty chamber?

    Sorry, I'm just a little slow. :p
     
  5. Jim V

    Jim V Member

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    I believe he thought that you were chambering the round by hand and then "dropping" the slide by releasing the slidestop. That causes abnormal stress on the extractor, they are not designed to work that way. Closing the slide on a magazine of dummy rounds duplicates the action of firing the pistol and is does not cause the stress on the extractor.

    If you have your pistol's slide locked back and release it on an empty chamber, it hits with more force that it would if the slide were picking up a round from the magazine. The chambering of a round cushions the slide going home.

    Dry firing either the 1911 or the Glocks w/o a snapcap will not damage the pistols.

    I hope this helps.
     
  6. mellow

    mellow Member

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    Thanks guys. Eggz-Aktly what I was looking for. :D
     
  7. Mal H

    Mal H Administrator

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    Jim's right. Your original post sounded to me like you were going to chamber a dummy and then drop the slide. Loading a mag with dummies and operating the slide is not a problem. (On the safety side, please be sure they are all dummies and don't have any live ammo in sight.)
     
  8. Bergeron

    Bergeron Member

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    Does anyone know how much the chambering of a round "cushions" the slide going foward?

    Looking at it from a mechanics standpoint, I would consider the chambering of round to be a non-deforming collision where both objects stick together, therefore

    mass_1*velocity_1 + mass_2*velocity_2=mass_(1+2)*velocity_3

    Let mass_1 be the slide, mass_2 be the round, and let
    mass_(1+2) be the slide and the round.

    Okay, now let's assume that a loaded round of .45 weighs twice as much as the bullet.(I know that this is a little high, but I don't have a precise way of measuring. If anyone knows, post it, and I will recalculate.) This is 2*230gr., or 2*14.9g (grains converted to grams).


    mass_2 = 29.8g

    The weight of a 5", .45 slide is 12.8 oz. (reference to www.sviguns.com/catalog2001/)

    There are 28.3495 grams in an ounce(reference to http://www.metrication.com/), so

    12.8 oz = 12.8*28.3495g
    12.8 oz = 363g

    mass_1 = 363g

    velocity_1 is the velocity of the slide before chambering, I don't know it, so I'll just call it v_i

    velocity_1 = v_i

    velocity_2 is the velocity of the round of ammo, zero

    velocity_2 = 0

    velocity_(1+2) is the velocity of the slide and ammo after chambering, I don't know it, so I'll call it v_f

    velocity_(1+2) = v_f

    Now subsituting into the equation

    mass_1*velocity_1 + mass_2*velocity_2=mass_(1+2)*velocity_3

    yields

    363g*v_i + 29.8g*0 = (363g + 29.8g)*v_f

    reducing,

    363g*v_i = 393gv_f

    deviding both sides by 393g yields

    0.924*v_i = v_f

    So that means that the final velocity of a five inch .45 round of ammo is slowed by about 10% by picking up a round of ball ammo. It seems to me that you could increase the slide velocity by a larger amount by simply shooting hotter ammo than ball, or by reducing the weight of the spring. I have never heard of shooting hotter ammo or reducing the weight of the spring to cause damage that is attributed to slamming the slide on an empty chamber.

    Also, if you consider the closing of the slide to be a collision on the internal parts, then it is appropriate to think in terms of momentum, by conservation of momentum and the equation above, same momentum hits the internals wether or not a round was chambered

    Kinetic energy of the slide-ammo has decreased, if ya'll want, I can figure out by how much the kinetic energy of the slide-ammo body decreases when you chamber a round.

    But based on these calculations, I don't see how the round of ammo would be able to slow the slide down enough to prevent battering of internal parts. I'm willing to be conviced however, so please review the calculations and help me find better data to calculate with!
     
  9. Shmackey

    Shmackey Member

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    I think you're looking at the movement of the slide toward the rear (shooter), as opposed to the movement of the slide into battery.
     
  10. Bergeron

    Bergeron Member

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    Looking at your statement, I agree that the ammo should not affect foward slide velocity(but I do not know this for certain), but the weight of the spring sure will.

    Lighter spring = slower foward velocity
    Heavier spring = faster foward velocity

    Also, will a 10% reduction in foward slide velocity really be the difference between a ruined trigger job?

    If you want, I can find foward slide velocities for 16, 18.5, and 20 pound springs. I know that guns with trigger jobs have at least these three weights. We can see if a 10% change in slide velocity from one spring to another exists. What do you think?
     
    Last edited: Dec 27, 2002
  11. eap

    eap Member

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    a glock armorer told me it's ok to drop the slide on an empty chamber.
     
  12. Gewehr98

    Gewehr98 Member

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    That 10% can make all the difference...

    Especially if you have a finely honed sear/hammer/disconnector system. I understand if you have a lightweight aluminum or carbon fiber trigger, the bounce of the trigger when the slide is dropped on an empty chamber can make things go South even more quickly.

    The extractor on the 1911 is much like the extractor on a Mauser, Springfield, Ruger, or pre-'64 Winchester Model 70. It's designed to ride over the cartridge rim as it's being picked up from the magazine. Trying to snap it over a chambered round can cause trouble, as anyone who's tried the same in a Mauser can attest. :(
     
  13. Shmackey

    Shmackey Member

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    Right. But in your previous post, you said that a lighter spring will increase the velocity.

    I'm just being a pain though; I know what you mean now that you clarified.

    All that aside, I am fairly sure that plopping a round in the chamber by hand and then dropping the slide is bad. Your internal extractor (which derives its springiness from nothing more than its bend) will get angry. I'm not so sure that dropping the slide on an empty chamber is bad, but I don't do it. And I've been indoctrinated enough to know that it's a newbie error. It's like using your forearm instead of a napkin at a nice restaurant--you won't break your arm, but come on!
     
  14. Bergeron

    Bergeron Member

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    Yeah, I was thinking about rearward slide velocity, and my statement was incorrect about foward slide velocity

    Thanks for pointing that out in your previous post. Made me think about it and realize that you were right, it's only gonna be the spring weight that gonna matter on foward slide velocity.

    Thanks.
     
  15. Bergeron

    Bergeron Member

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    And now I have a question. I really want to look at the different spring weights like I mentioned in my earlier post.

    I don't have a 1911, so I'm going to need some help on this. How much does the spring on a 5" 1911 compress and what is its initial length?

    When the "weight" of a spring is mentioned, is its spring constant actually being referred to? i.e., does an 18lb spring have an 18lb per inch?/foot?/whatever? spring constant?
     
    Last edited: Dec 28, 2002
  16. Shmackey

    Shmackey Member

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    I'd bet dollars to donuts that they're not thinking about spring constants or anything formulaic.

    More likely that a pillowcase full of them weighs 18 pounds.
     
  17. Bergeron

    Bergeron Member

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    LMAO, Yeah, you're probably right!

    But I did get an inspiration: I'll email Wolff, they've gotta be able to tell me something.
     
    Last edited: Dec 28, 2002
  18. Mike Irwin

    Mike Irwin Member

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    I asked Mac Scott, of Scott McDougal gunsmithing this very question some years ago.

    Without going into a long drawn out recounting of his reply, most of which I don't recall anyway, I'll stick with his advice -- don't let the slide slam home on an empty chamber. It can hurt the gun.

    I figure this man knows. He's built probably a couple metric tons of highly tuned 1911s.
     
  19. Wildalaska

    Wildalaska member

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    Mr. McDougal has the same opinion as 99% of the custom gunsmiths out there....
     
  20. F=ma

    F=ma Member

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    Hey Bergeron...

    ...Remember to include the frictional force caused by the mag spring against the lips/carrier/next round. If you really wanted to get picky, you could also include the "cushioning" collision of the round on the feed ramp.
    (Now what's the angle of that ramp? :D )
     
  21. Bergeron

    Bergeron Member

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    Yeah, you're right, but I don't think that those details will affect my answer as much as getting better measurements.

    Besides, I for sure don't have equipment to measure either of those.

    Would be more interesting, but I don't think that the answer would be much more accurate.
     
  22. HS/LD

    HS/LD Member

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    There is NOTHING wrong with dropping the slide on an empty chamber!

    It is am old myth.

    If your handgun will be screwed up by dropping the slide on an empty I suggest you buy another handgun.

    IMHO:D

    HS/LD
     
    Last edited: Dec 28, 2002
  23. Gunhead

    Gunhead Member

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    What wrong? Nothing, if you buy a real pistol, not something else... ;)
     
  24. Blackhawk

    Blackhawk Member In Memoriam

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    I tune my extractors so they will swing to allow the slide to slam home on a casing in the chamber so the extractor can catch the rim to extract it when the slide's pulled back.

    That involves reshaping the extractor claw so it meets the rim with a ramped surface instead of a surface parallel to the back of the casing.

    Why? There are some jams with some guns that result in the just fired casing ending up back in the chamber. They can be caused from any number of variable situations involving lube, heat, angle of the muzzle during firing, etc., and the jams cannot be predicted. But I KNOW they happen!

    They're not "quick" to clear because you have to (1) figure out what happened, (2) lock the slide open, and (3) point the muzzle up and possibly "help" the spent casing fall out. Bottom line is that those jams put your gun out of commission for MANY seconds since even if you KNOW what's going on, clearing is very awkward.

    Extractors are cheap, and the modification doesn't affect anything strength wise. I certainly don't want to have an experience with this type of jam in a SD social situation.

    To test the modified extractors, I manually insert a casing and slowly let the slide close with the extractor spring exerting enough pressure that the recoil spring can't overcome it. A bit of a bump on t he back of the slide causes the extractor to ride over the rim and lock shut. Then I test it a few dozen times letting the slide slam home.

    IMO, the modification makes the pistol more reliable because it greatly lessens the chances of the extractor claw breaking if it should slam home on a still chambered casing.
     
  25. Wildalaska

    Wildalaska member

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    You guys dropping that slide sure make gunsmiths happy :)

    Got sights on the side of the slide too do you....???

    On the extractor mod...thats how they are supposed to be tuned...but it is for situations where closing on a chambered round is unavoidable. Doing it deliberatly is poor and improper technique.
     
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