The M25 Gas Cylinder Mod - M14 Forum

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The M25 Gas Cylinder Mod

This is a discussion on The M25 Gas Cylinder Mod within the Reference forums, part of the M14 M1A Forum category; I'm posting this because the information has been scattered amongst other forums and I hate having to keep finding it. The information was on a ...


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Old February 21st, 2017, 06:21 AM   #1
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The M25 Gas Cylinder Mod

I'm posting this because the information has been scattered amongst other forums and I hate having to keep finding it. The information was on a thread here on the forum but the picture links were dead, so I'm updating them with Josh's updated links.

The posts below are from Josh (NoExpert) and T44E4 (I think he's SOCOM42 on this board but hasn't been back in a long time).

It is a .0625" hole at 6 o'clock in the trepan groove.
The purpose of the hole is to allow the silica deposits from the blow-by gasses to be vented, thus preventing a buildup of said deposits. The piston acts as an air pump to force out the residue.
Those deposits will ruin any coating on a piston by attacking the substrate.
If you look at any piston that has at least a hundred rounds on it, you will see the scoring, it is right at the end of the large diameter at 6 o'clock (at the back). The scoring gets worse as the buildup increases and can cause permanent damage to both piston and cylinder.








From SOCOM42 (AKA: T44E4 on another forum)
.0625" drill,
center of groove,
must be at six o'clock only.
Smaller drill will constrict flow, larger will loose velocity.
That 1/16" i guess will do the job.

The groove is there as a relief for the cylinder hone and the burnishing tool.

IT IS .210"+.005"-0" FROM THE BACK END.
This dimension is based on GI cylinders, cannot speak for aftermarket units.
For those, you will have to calculate the distance yourself.


Tony.

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Old February 21st, 2017, 07:19 AM   #2
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Try to get all the info you can from T44E4;as he is not in good health.

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Old February 22nd, 2017, 03:58 PM   #3
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Thank you for posting this Tony.
I've been thinking about this for a couple days now and yours was the first post to pop up in you seach.

Ed

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Old February 22nd, 2017, 07:01 PM   #4
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Mine was done a long time ago, shortly after NoExpert did his. And yes it works well, just look at the carbon streak in his pic. That much less carbon too wipe off or scrape out of the piston and over time it adds up. Another real neat thing is that with a normal stock the carbon just shoots out the bottom of the stocks weep hole, this modification is unseen when the rifle is assembled.
Attached Images
File Type: jpg M-25 vent mod.jpg (16.2 KB, 10 views)
File Type: jpg Gas Cylinder Mod.jpg (31.5 KB, 15 views)

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Old February 22nd, 2017, 07:24 PM   #5
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Quote:
Originally Posted by Foxfire32 View Post
Thank you for posting this Tony.
I've been thinking about this for a couple days now and yours was the first post to pop up in you seach.

Ed
Well worth doing.

From inside:



Last edited by NoExpert; February 22nd, 2017 at 07:36 PM.
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Old February 22nd, 2017, 08:21 PM   #6
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Quote:
Originally Posted by NoExpert View Post
Well worth doing.

From inside:


Excellent pic!!! My camera will not resolve that small and show the detail. For lack of a better description you can sell how the G/C inside tail wall gets used as a flow director, now there is nowhere for the chunks of junk too go but get blown out.

What we all forgot too mention was that using a smaller blow hole and stuff doesn't all get evacuated, too big and the port will stall not evacuating everything either.

And for those guys with bedded rifles that fear cleaning take downs this mod also helps keep moisture attracting carbon off the underside of your barrel fertilizing and getting those pesky rust specs growing.

In my opinion this should be a every rifle mod not just Match Rifles, it works equally well on non-bedded or USGI barreled rifles too extending the inside piston cleaning interval...

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Old February 22nd, 2017, 08:33 PM   #7
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Quote:
Originally Posted by Phil McGrath View Post
Mine was done a long time ago, shortly after NoExpert did his. And yes it works well, just look at the carbon streak in his pic. That much less carbon too wipe off or scrape out of the piston and over time it adds up. Another real neat thing is that with a normal stock the carbon just shoots out the bottom of the stocks weep hole, this modification is unseen when the rifle is assembled.
Phil, do you still get carbon on the end of the oprod from the blow back out the rear of the gas cylinder. It is it eliminated completely by going out the hole?

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Old February 22nd, 2017, 09:21 PM   #8
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Quote:
Originally Posted by Capona View Post
Phil, do you still get carbon on the end of the oprod from the blow back out the rear of the gas cylinder. It is it eliminated completely by going out the hole?
No it not eliminated completely, I get about 95% less than what was there before norm. But a lot of it also depends on how much the pistons tail fills up the "D" shaped hole in the rear of the G/C.

I have a Bula Nitrated Piston in a USGI Unitized gas cylinder that fits like a puzzle piece in the "D" hole with almost no gap or L/R piston rock.


The other USGI unitized G/C with its SADLAC TiN grooved piston shows just a weee faint line of gold in the "D" hole so there is slightly more L/R piston rock, that with the groove allows a little more crud get past.

Both piston tails measure the same so the "D" hole in one G/C is a little tighter than the other one, but both showed about a 95% reduction from there norm and I use 4895-4064-Varget-4320 powders.

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