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Thread: Slamming the breech block Home

  1. #1
    Senior Member USES HIS SCAR AS A PILLOW
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    Slamming the breech block Home

    Ok, I will divulge.

    as you all know, the barrel recoils inside the receiver. It is held in place against the receiver via ribs on the barrel itself. One of 2 ribs are fore and 1 rib aft.

    The ribs are a smaller diameter than the aluminum cast receiver and thus a prominent barrel slop occurs. If you wiggle the barrel you will notice at leas a 2 MOA travel. If you push down on the barrel, it will move rearward.

    The rearward travel is stopped by the barrel shroud - not a big problem since the energy dissipated to the receiver is not that great.

    But what stops the forward travel when the breech block slams against the barrel?

    I have taken some exact measurements to make sure, but it is the barrel slamming against the receiver. What is worse, there is only a small amount of aluminum in a form of a ring that is preventing the barrel from
    going any further forward. When the gun is assembled, the push down disassembly pin aids in the damage, but because it is not part of the receiver, it only helps from total disintegration of the ring.

    So what gives? The barrel has a bigger diameter at the chamber (for about 2 inches) then it has a shoulder and tapers down to a thin barrel that you can see is inside the long spring that retards the cocking handle.

    This shoulder slams on the receiver's ring of aluminum that is only about 1/4 inch thick. I have fired about 500 rounds through mine and I can already see some peening.

    hence - this whole process of deforming the receiver is exacerbated if you do not have a round in the mag. As the breech block travels forward, it has to stripe another round (looses velocity and momentum) then the friction of the round going into the barrel scrubs some of this momentum also.

    Without the round - you will hear this LOUD and very metallic CLANK!!

    That is bad, very very bad for your weapon. I have done it before not realizing what the internals were doing.

    Of course, pictures are forthcoming on the web site, so please be patient!
    Between babysitting my 3 year old princess and the yard, I will try to manage to post them tonight.

    There ya have it fellas.

    TH


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  3. #2
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    Here is the page I promised including pictures.

    http://ps90forum.com/Receiver.html

    TH
    Jack Mobes thanked this.

  4. #3
    Senior Member KIRK'S AWAY TEAM (blue shirt) metroplex's Avatar
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    I think the cocking handle spring dampens some of the force, albeit not a whole lot. I've noticed my barrel moving rearward when the breech block leaves the breech. When the breech block comes back, the barrel moves forward a little. When the hammer is released, the barrel moves forward a little further.

    I have read that the barrel was designed to travel rearward to increase "dwell time" for the case so that the chamber pressure subsides a little.

  5. #4
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    Quote Originally Posted by metroplex
    I think the cocking handle spring dampens some of the force, albeit not a whole lot. I've noticed my barrel moving rearward when the breech block leaves the breech. When the breech block comes back, the barrel moves forward a little. When the hammer is released, the barrel moves forward a little further.

    I have read that the barrel was designed to travel rearward to increase "dwell time" for the case so that the chamber pressure subsides a little.
    You are absolutely correct!

    TH

  6. #5
    Senior Member Bullseye Shooter
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    Wow! Has this been brought to FN's attention? If so what do they have to say about it?

  7. #6
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    Quote Originally Posted by ArmChairCommando
    Wow! Has this been brought to FN's attention? If so what do they have to say about it?
    I won't bother them with it - but anyone here can give it a shot. I'm sure you will get replies like it's never bothered anyone, it works and so on. Besides, it's too late to augment this weapon to any degree.

    I just bring it to the community's attention that slamming the breech block is hard on the gun. All we can do is minimize abuse and prolong longevity.

    You got to realize that military or LEO do not care about such issues and most probably, when they return the weapon to FN for service, FN replaces all the worn parts. It's only the average civilian that saved for a year that cares about such matters.

    The Berreta M9 has similar issues and at $600 a pop, they replace the slides after only 5000 rounds - MANDATORY. (you all remember the horror stories about the slide in the head thing)

    TH

  8. #7
    Senior Member KIRK'S AWAY TEAM (blue shirt) metroplex's Avatar
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    Right, you'll get the typical "the P90 has been used for decades by speshul forces and no one complained but you..."

  9. #8
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    Right!

    The only wheapon I would consider "open source" is the AR, since there are sooo many manufacturers, and if you do not correct an issue, some other manufacturer will and upsell you on the weakness.

    So what iteration of the AR are we on now? The gas pistons being the latest incarnation from POF, Barret and HK?

    These are the little things that the factory does not want to "get out" - especially if they are the sole manufacturer of the weapon.

    I own a bunch of HK weapons and they all have weaknesses. PS90 weapon is no different. The trick is knowing what they are. I also own a custom built AR M4 from preimum parts and I love it. (different role and application than the PS90)

    Aren't firearms fun?


    TH

  10. #9
    Max
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    so i guess the only remedy would be to minimize the damage by riding the breech block forward if you're not chambering a round. correct?
    Use your rights. It means I'm doing my job.

  11. #10
    Senior Member USES HIS SCAR AS A PILLOW
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    Quote Originally Posted by Max
    so i guess the only remedy would be to minimize the damage by riding the breech block forward if you're not chambering a round. correct?
    Correct!

    TH

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