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Discussion Starter #1
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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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. :?:
 

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Discussion Starter #4
metroplex said:
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! :D

TH
 

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Discussion Starter #6
ArmChairCommando said:
:shock: Wow! :shock: 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
 

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Discussion Starter #8
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
 

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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? :?
 

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maybe is a total stupidity the thing that I will say; but put a stainless stell washer in those alu rings will not solve the problem...??
or the distance is critical..?

(electrolysis apart..¿?)
 

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Discussion Starter #12
Mad-o-Vic said:
maybe is a total stupidity the thing that I will say; but put a stainless stell washer in those alu rings will not solve the problem...??
or the distance is critical..?

(electrolysis apart..¿?)
1. Distance is critical. You would then have to lathe off the same amount of thickness from the barrel shoulder to compensate.

2. At the same time, I'm not sure that the steel washer would not bind, or fuse with the barrel, and in the end - cause the same problem.

The only thing that could be attempted is a shock-buf type polymer ring that would then have to be fast attached to the barrel, and then be able to be replaced every so often. I'm not sure that this amount of custom work would be worth to mitigate the damage that is being done to the receiver.

This type of manufacturing change would have to come directly from the factory.

Cheers,

-M
 

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Yes I gess that this is a lot of work and research for solving this problem....

Maybe to lathe the barrel 0.5mm and insert an O-ring... but who knows...

:lol:
 

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Since the bolt on the PS90 does not hold open on the last shot, does this mean that you are potentially damaging your rifle everytime you fire the last round in the magazine?
 

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Discussion Starter #15
D-Rock said:
Since the bolt on the PS90 does not hold open on the last shot, does this mean that you are potentially damaging your rifle everytime you fire the last round in the magazine?
You got it.

-M
 

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:idea: How about using a spent cartridge to make a snap cap? Insert it into the magazine FIRST, before shooting practice. When you get to the end of the magazine, it will load and you will strike the snap-cap instead.

You can make a snap cap easily- seat a bullet onto a primerless, resized case. Drill a small hole in the side of the case, then fill the cartridge with silicone RTV caulk until it comes out the relief hole. Fill the primer pocket completely. You may want to mark the cartridge with a magic marker or wash in ink to make it stand out. I make snaps for every caliber I shoot this way. The silicone stands up to the firing pin each time and I have yet to wear one out.

I was wondering about the bolt on an empty chamber when I was firing my PS-90 the other day. Everything is made of plastic or aluminum on this rifle! I thought this might help if it was actually a problem, but thought that FN wouldn't let a design flaw like that happen. Then I read this post and woke up!

Just throwing it out there...
 

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Discussion Starter #19
gunbunny said:
:idea: How about using a spent cartridge to make a snap cap? Insert it into the magazine FIRST, before shooting practice. When you get to the end of the magazine, it will load and you will strike the snap-cap instead.

You can make a snap cap easily- seat a bullet onto a primerless, resized case. Drill a small hole in the side of the case, then fill the cartridge with silicone RTV caulk until it comes out the relief hole. Fill the primer pocket completely. You may want to mark the cartridge with a magic marker or wash in ink to make it stand out. I make snaps for every caliber I shoot this way. The silicone stands up to the firing pin each time and I have yet to wear one out.

I was wondering about the bolt on an empty chamber when I was firing my PS-90 the other day. Everything is made of plastic or aluminum on this rifle! I thought this might help if it was actually a problem, but thought that FN wouldn't let a design flaw like that happen. Then I read this post and woke up!

Just throwing it out there...
Excellent post GunBunny!

:D

-TH
 

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gunbunny said:
:idea: How about using a spent cartridge to make a snap cap? Insert it into the magazine FIRST, before shooting practice. When you get to the end of the magazine, it will load and you will strike the snap-cap instead.

You can make a snap cap easily- seat a bullet onto a primerless, resized case. Drill a small hole in the side of the case, then fill the cartridge with silicone RTV caulk until it comes out the relief hole. Fill the primer pocket completely. You may want to mark the cartridge with a magic marker or wash in ink to make it stand out. I make snaps for every caliber I shoot this way. The silicone stands up to the firing pin each time and I have yet to wear one out.

I was wondering about the bolt on an empty chamber when I was firing my PS-90 the other day. Everything is made of plastic or aluminum on this rifle! I thought this might help if it was actually a problem, but thought that FN wouldn't let a design flaw like that happen. Then I read this post and woke up!

Just throwing it out there...
Can you make me one?
 
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