PS90 Mag Popping Theory

Reloading info for the 5.7x28mm

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iFire
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PS90 Mag Popping Theory

Post by iFire » 10 Jan 2011, 11:06

Ok - to those who have asked me about my mag popping up (or lack there of...)

I hadn't experienced this that much with any of my loads. However, I may have finally figured out why....

In most of my tests i have been using high(er) pressure loads - I havent loaded that many rounds for my PS90 that are "strong plinkers" for example... And this could be why...

I did have the mag pop up twice last time out testing - i was using 6.3 grains of True Blue with a 40 gr Vmax - these two occurences now put me at three total times experiencing this. The first time i had it pop up I *think* i was using a midrange load of A#7 (~7.0gr).

My theory:

There is a window with certain powders where the case has enough pressure to eject strongly, pushing up the mag, BUT not enough pressure to get a good strong grip on the chamber, which would slow ejection a bit and prevent the mag from popping up.

Here's an example of what i mean - This may not be the right range, but for the purpose of example:

40gr Vmax
True Blue

≤ 6.1 grs. - function is good, not to much pressure upon ejection, mag doesnt pop up
6.2-6.4 grs. - too much pressure pusing back, but not enough gripping the chamber - mag pops up
≥6.5 - enough pressure to grip the chamber strongly, slows ejection, mag does not pop up

Of course, all theories need to be properly tested and re-tested...

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Re: PS90 Mag Popping Theory

Post by panzermk2 » 10 Jan 2011, 13:29

This would be one of the causes and why it's been hard to nail it down. Just like LilGun not allowing the case to grip the chamber and even at low charge levels having brass issues in the FsN.
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Re: PS90 Mag Popping Theory

Post by flyingirish04 » 10 Jan 2011, 16:07

Every variation of EA rounds I shot popped up the mag at least once in the course of emptying a magazine. At no time did it happen with FN ammo. My groups with FN ammo were terrible though, not so with EA.

I don't see a reason to shoot the PS90 without EA loads, so I sold my PS90. My cousin had the same situation happen to him. I love EA more than I love the PS90, so bye bye PS90.
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VeTTeMaNC486
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Re: PS90 Mag Popping Theory

Post by VeTTeMaNC486 » 11 Jan 2011, 12:09

Forest Fire wrote:Ok - to those who have asked me about my mag popping up (or lack there of...)

I hadn't experienced this that much with any of my loads. However, I may have finally figured out why....

In most of my tests i have been using high(er) pressure loads - I havent loaded that many rounds for my PS90 that are "strong plinkers" for example... And this could be why...

I did have the mag pop up twice last time out testing - i was using 6.3 grains of True Blue with a 40 gr Vmax - these two occurences now put me at three total times experiencing this. The first time i had it pop up I *think* i was using a midrange load of A#7 (~7.0gr).

My theory:

There is a window with certain powders where the case has enough pressure to eject strongly, pushing up the mag, BUT not enough pressure to get a good strong grip on the chamber, which would slow ejection a bit and prevent the mag from popping up.

Here's an example of what i mean - This may not be the right range, but for the purpose of example:

40gr Vmax
True Blue

≤ 6.1 grs. - function is good, not to much pressure upon ejection, mag doesnt pop up
6.2-6.4 grs. - too much pressure pusing back, but not enough gripping the chamber - mag pops up
≥6.5 - enough pressure to grip the chamber strongly, slows ejection, mag does not pop up

Of course, all theories need to be properly tested and re-tested...
The only time mine has popped was when I used blue dot and 55gr fmjs. I did five rounds each 5.5gr - 6.0gr, I do not remember exactly how many popped at what charges but I do remember that from 5.6-6.0 atleast one of the five popped the magazine. I also had alot of spent casings get stuck between the back of the barrel and the bolt. Interesting note is that at 6.0grs I did not even have any primer leakage or lost primers.

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Re: PS90 Mag Popping Theory

Post by iFire » 19 Jan 2011, 18:09

Another addition to the Theory...

Could it be that the increased recoil causes enough jarring of the gun that the mag catch moves, even if just slightly, allowing the mag to pop up?

Here's why. The mag is on the gun really tightly, and even if you try to pull up on the mag, really hard, you cant pull it off... So, that is why I am thinking that it almost "must" have something to do with the mag catch.

To test this theory I altered the spring configuration of the bolt. I placed a highered powered 1 3/4" spring on the guide rods along with the original spring with 15 loops cut off... The higher powered spring greatly reduces the impact of the bolt recoil in the last 1" of movement, and seems to have completely eliminated the mag popping up.

see thread viewtopic.php?f=16&t=9622&p=144186#p144186" onclick="window.open(this.href);return false;

I havent had the mag pop once in around 150 rounds:

10 ss197's
25 40gr Vmax's with True Blue @ 2200 fps
50 40gr Vmax's with A#7 @ 2300 fps
50 40gr Vmax's with True Blue @ 2500 fps
10 40gr Vmax's with True Blue @ 2550 fps

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