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This is a discussion on Piston chat.. within the Art Luppino forums, part of the Gun Professionals category; Originally Posted by Capona tony, it doesn't eject brass as far? Or at a different clock position? The brass doesn't eject as far. Most of ...

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Old December 13th, 2016, 04:18 AM   #31
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Originally Posted by Capona View Post
tony, it doesn't eject brass as far? Or at a different clock position?
The brass doesn't eject as far. Most of it (the SPEER 125's) just kind of falls out of the action and it gently rolls off the bench.


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Old December 17th, 2016, 11:06 PM   #32
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Could you give us an idea of what you consider a fast piston vs. a slow piston?

My old M1A, which has always shot as well as I could ask it to, currently has a piston (Sadlak) in a USGI unitized gas cylinder (Hueygunner) that, when I point the rifle up at 45 degrees and lock the bolt back, I can just say "Mississippi" then *click*. It's about a second or a bit less.

What would a fast or slow piston be, say in Mississippis?

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Old December 18th, 2016, 05:56 AM   #33
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Originally Posted by jywolfe View Post
Added a piston worksheet. Headed to the range and will update later.

Measured diameter at port, diameter at tip, total indicated runout from those locations, face concentricity and mass.

Note the difference in diameter for Brookfield Piston.
According to the drawings, only four of the listed pistons are to print.

#1, #5, #7, and the Bula

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Old December 18th, 2016, 06:04 AM   #34
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Originally Posted by XM25Ren View Post
Not an expert but I do know that the NM grooved piston was meant for the heavier bullets ie. 168 and 175. Anything lighter may not cycle the action.

The stock GI M14 gas system is over gassed, for the average shooter in temperate weather. It was designed to work with the lowest possible expected port pressure in arctic climatic conditions, without lubrication.

It can leak, loose, have bleed off, a lot of gas before it starts to have serious trouble.

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Old January 24th, 2017, 08:58 AM   #35
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piston tilt test surprise

Regarding my comments of early December in Post #10 in this thread:

Is it too late to return to that briar patch? I would like to report a recent experience which contradicts my comments above.

During the three years of my membership, I have read many comments about the value of the tilt test, which miffed me for several years because, as previously recorded, my gas piston fell ceremoniously when I had gas cylinder shims installed and fell rapidly with the gas plug removed or loosened. I attributed that to a condition recently described as "vacum drag." The tilt test is considered by many to be a "litmus test" of a rifle's operational health.

Pursuant to recent related discussions about shims, pistons, unitized gas cylinders, and egcetra, I removed my shim in preparation for my next range visit and testing. (I tapped my GC assembly forward gently to achieve a 5 o'clock finger-tight gas lock situation.)

As an after thought, I decided to conduct another tilt test (no shims, gas plug tightened sufficiently). Incredibly, the piston fell like a rock in both directions.

It appears to me now that there was no vacuum in the GC. Rather, the light tightening of the GC against the barrel shoulder and shim was distorting the GC!!

What do you all think?

I will soon report separately about changes since my last range visit.

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Old January 24th, 2017, 09:31 AM   #36
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Gas Cylinder installation

Installing the gas cylinder on the barrel in hopes of producing the best accuracy can lead to issues. In the attempt to install the cylinder in a non-movement position interferes with the normal slip fit of a standard grade rilfe cylinder installation.

Add to this the use of shims and the cylinder can be put under stress, using the popular method of having the lock hand tight to 5 oclock. Now three things have been added, peening and shims and a tight lock..

This combination of modifications often puts stress on the cylinder, this stress influences the piston, which accounts for slow piston action.. To make matters more difficult the heat changes all of the above.

What does all this mean?

Always check piston fall when the barrel up to temp, at least ten rounds fired.. If the piston is dragging, slow or jerky now is the time to change pistons, "Piston Change out".

The above may be ther reason the Army used the "Pull Forward" system insrtalling the gas cylinder, in stead of shims.. Sometimes the Army makes good decisions.. The shim system is excellent but can require making adjustments to the lock going from 5 to 5:15 and so on..

The lock is not a hand tight one position for every rifle, you have mess with it sometimes.. Art

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Old January 24th, 2017, 11:38 AM   #37
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Interesting. I will keep that info in mind.

I always make sure the pistons fall free when cleaning. I guess I will keep it up.

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Old January 24th, 2017, 01:55 PM   #38
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Not sure it was worth our time, but we still talk about the all-day nearly-straight rod

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Old January 24th, 2017, 02:08 PM   #39
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Anybody know how to

Move my Thread on cyl installation to a new Thread// Would appreciate it being done... Art

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