MP5/40 Case Separation
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Thread: MP5/40 Case Separation

  1. #1
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    Default MP5/40 Case Separation

    Took my MP5/40 to the range for the second time yesterday.

    First time out we had one FTEject out of about 150 rounds of Remington 180 grain Green box. Ejection was about 4-5' to the RF with a #26 LP. Feedback I received at the time suggested trying different ammunition as GB was noted as being low powered.

    Yesterday we ran 100 rounds of Winchester 165 grain white box with no issues. Had 80 rounds of GB still in the range bag so we decided to run it to. Had another FTEject similar to what happened the first outing. Later had another FTEject but this time it was different in that the case itself separated neatly 360 degrees about 0.375" back from the case mouth. The rear part of the case was sitting in the action jammed against the next round that tried to feed. The front section was stuck in the chamber. We actually inspected the chamber and thought all was well but when we closed the bolt on a fresh mag the bolt would not close. Pulling back on the cocking knob ejected both the loaded round plus the front part of the separated case. And this was with the 'low powered' Remington green box ammo.

    I used to reload for benchrest shooting for years and never had any cases separate. Plus the kind of case separations associated with bolt action rifles would normally occur closer to the cartridge rim, not sort of midway through the length of the case. At any rate, case separations are not something I like to mess with.

    See photos for more insight.

    Has anyone seen anything like this with an MP5 or MP5-40?

    MP5/40 Case Separation-case2.jpgMP5/40 Case Separation-case1.jpg
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    I have not had this issue because I do not shoot reloads, but this issue is common with reloads. The repeated expansion and contraction of the casings, especially in roller delayed guns, weakens the casings.
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    Not had that happen in my .40 clone. I took in some Remington green box in trade that I will be moving onto next.

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    This may be a 40 cal. issue more than 9mm

    I am only my 4th reload on 9mm casings on my Dillon RL550B and havent had any issues. I do the typical shoot, tumble/clean and then reload. Time will tell!

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    Ive had it happen in my 40 clone .....
    factory ammo ......

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    Quote Originally Posted by Marine0303 View Post
    I have not had this issue because I do not shoot reloads, but this issue is common with reloads. The repeated expansion and contraction of the casings, especially in roller delayed guns, weakens the casings.
    Sorry for the confusion here - the separated case was with factory Remington 180 grain green box ammunition.

    The other reference was about bolt guns when I used to benchrest. Handloaders were always taught to be aware of signs of pressure.

    And, for the record, the separated case does NOT show signs of pressure around the primer such as one would expect to see. This seemed to be more like the case being ripped apart mechanically, except what was strange was the fact that it was so uniform araround the circumference of the case.

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    Quote Originally Posted by FRANK View Post
    Ive had it happen in my 40 clone .....
    factory ammo ......
    Do you recall what kind of ammo you were using? Did it appear to be a pretty clean break straight around the case like this?

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    Quote Originally Posted by swiss_seth View Post
    This may be a 40 cal. issue more than 9mm
    I've seen it happen a few times on my 9mm clones. One time I know why it happened. Miss feed and a lightly crimped projectile got set back a bit, and when it was chambered, and fired it was WAY WAY over pressure. Back 1/ 2 of the case disintegrated.

    I've had some(2-3 other) 9mm separations that were not (as far as I know of) due to over pressure. But I've not tracked it down to a source.

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    It happened to me in a MP5/10 clone. For me the separation occurred right above the rim, with DoubleTap ammo.

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    Please assist us with a little more information.
    Weapons Maker / Barrel Maker
    Possible date of and/or first (3) serial number of the weapon - This may assist with year of built and/or barrel manufacturing date/Run.

    Would it be possible to get a picture of the chamber - i.e. the chamber flutes on the case look light.
    A suggestion - (3) different types of 40 cal ammunition - Bright LED and/or flash light - Clean the barrel & Flutes to the best of your ability - separate the upper from the lower and pull the complete carrier and spring guide from the weapon - Now seat a round in the chamber and flash the light through the front of the barrel - Take a picture and show us of all three - if you have another H&K with fluted barrel do the same and compare.

    If memory serves me right some of the older clone 40 Barrels were over sized and/or were cut with a worn reamer....That's what some the older threads on the board stated.
    Hope this helps.

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