M14 / M1A / M305 Gas System Accurization & Durability / Self Cleaning Modifications

Sh0ckw4v3

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M14 / M1A / M305 Gas System Accurization & Durability / Self Cleaning Modifications

Before I begin, let me state that I've learned a tremendous amount from this community and its members - if I've learned anything it's how much I still don't know about firearms and marksmanship - and I'm continuing to learn as much as I can. I'd like to give back to the community, and this is my first effort to do so, so if you have any feedback, corrections, or other contributions please don't hesitate to submit them here. :)

Gas System Accuracy Modifications

Many threads on this forum have been dedicated to accurizing the M14 platform; while the gas system is often mentioned (by way of unitization and shimming of the gas lock), the significance of the gas system on the accuracy of the rifle still doesn't seem to be widely understood. Somewhat counter intuitively, disabling the gas system on these rifles by way of the spindle valve tends to have a negative effect on accuracy, making it difficult to isolate gas system issues.

What seems more common knowledge south of our border, and much less so in Canada, is that the simple act of switching out gas pistons has been proven to reduce group sizes considerably (from 4 - 5 inches at 100 yards to under 2 inches in many rifles with all other variables kept consistent).

The type of piston seems unrelated to the effect on accuracy: while a premium piston such as a Sadlak typically typically offers some improvement in most rifles, in some rifles a well worn piston provided better results.

With most of us owning a Chinese variant of this platform we're unable to interchange gas pistons easily with aftermarket offerings due to the variance in geometry between American gas cylinders and pistons and their Chinese counterparts, leaving us with either the option of replacing the entire gas system with the exception of the gas lock (which needs to remain on a Chinese barrel due to difference in the threading) or switching out Chinese pistons until a good match for the rifle is found.

I would like to propose gas piston exchanges, where several members from the same area get together to swap pistons in an attempt to improve the accuracy of all rifles present. I'm not sure if Barney does this at his clinics as I have yet to attend one (we've met, though), but that certainly would be an excellent place to start if that's not currently the case.

Durability / Self Cleaning Modification

Once a good piston is found for a rifle, keeping that piston and cylinder combination in top condition should be the next priority.

Though the M14 gas system was designed as self cleaning, those of us who have fired more than a box or two of rounds through our rifles know that's not exactly the case: carbon and silica deposits still accumulate on the piston and the tube, and will eventually cause significant wear on both parts. This is largely due to the gas system's self cleaning action only functioning in one direction of the piston's stroke.

There exists a remarkably simple modification that can be made to the gas system tube which allows the piston to self clean in both directions of the piston's stroke, effectively eliminating gas piston wear - member T44E4 on m14br.com details the modification below:

http://www.m14br.com/showthread.php?14474-Added-a-third

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.

DSC00147.jpg


IMG_0368.jpg


IMG_20140213_174855_827.jpg

The details of the modification follow:


http://www.m14br.com/showthread.php?15904-For-T44E4-and-all-those-who-ask-about-the-M25-vent-mod


.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.

If a vendor on this forum would adapt the measurements given to Chinese gas systems and start offering this service for a reasonable cost it would be of great benefit to anyone with an accurate M14 pattern rifle.
 
-Sh0ckw4v3
Interesting idea. It is not clear to me exactly why you are drilling the hole described. There is some clearance between the tail of the piston and the rear of the gas cylinder. Would not some soot be ejected on the rearward stroke by virtue of this clearance? Thanks.

Normal operation of M14 gas system.

Gas from the barrel enters the floating piston through a hole in line with the barrel gas port, and fills the space within the piston and gas cylinder plug. The first movement of the piston takes the hole out of alignment with the gas port and cuts off admission of gas. The considerable volume of trapped gas expands smoothly and pushes the piston and operating rod to the rear. By the time the piston clears the exhaust port at bottom of the cylinder, the work of the gas has been done.

2010721153712-m14gas_f.jpg
 
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I've experienced excellent results by installing the Smith Enterprise SBR Hard Chrome Piston in their M80HT Gas Cylinders.
The radiused grooves on the SBR piston enhance cleaning and carbon removal.
I also use SEI's extra volume Socom gas plugs on shorter barrels, and rifles I suppress.

The Self Cleaning Modification has intrigued me for some time, but I've never seen any conclusive data supporting the performance claims.
 
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Member T44E4 is Mr. Brookfield, himself. As in Brookfield scope mount, Brookfield NM spring guide...

He knows his stuff and the mod is legit. It works, PERIOD!

Tony.
 
Thank you for all of the comments so far.

Interesting idea. It is not clear to me exactly why you are drilling the hole described. There is some clearance between the tail of the piston and the rear of the gas cylinder. Would not some soot be ejected on the rearward stroke by virtue of this clearance?

There is blow-by intentionally designed into the gas system: the piston is intended to float down the cylinder on blow-by gasses, dramatically reducing the wear on both the piston and the cylinder as a result. It's a brilliant design, but the result is a gradual accumulation of deposits from those blow-by gasses which will inevitably wear the system out. There isn't enough volume of gas escaping from the rear of the gas piston to clean it out, and the solution, though extremely precise in implementation, is to simply drill a hole at the end of the system to permit the piston to push out the deposits without interfering with the blow-by effect.


Thank you for the excellent illustration.

Member T44E4 is Mr. Brookfield, himself. As in Brookfield scope mount, Brookfield NM spring guide...

He knows his stuff and the mod is legit. It works, PERIOD!

Well that certainly explains his knowledge! I haven't been in the M14 community long enough to know who everyone is, but I've downloaded all of your videos and have referenced them many times - thank you for creating such an excellent resource for the community.
 
so where abouts is the new hole in relation to the existing gas vent hole? Is it closer to the gas plug, or towards the op rod? If closer to the oprod, that would place it within the stock?
 
I've talked about swapping gas pistons many times here and at the clinics I've put on. Gus fischer wrote some good posts about this a bunch of years ago. Since then I've kept 2 small parts bins with numerous GI spec and norinco gas pistons just for the purpose of finding that "one" that the rifle likes the most hehehe.
Have to admit, haven't read much on the cylinder "improved self cleaning" mod as I haven't spent much time on the US forums in a long long while.
Looks like a neat mod though.
 
Gee Gawds!

When my ninco piston did not fit my GI spec cylinder I just threw the piston in my lathe, took a few thou off and polished her up.

Still working. :)

I've talked about swapping gas pistons many times here and at the clinics I've put on. Gus fischer wrote some good posts about this a bunch of years ago. Since then I've kept 2 small parts bins with numerous GI spec and norinco gas pistons just for the purpose of finding that "one" that the rifle likes the most hehehe.
Have to admit, haven't read much on the cylinder "improved self cleaning" mod as I haven't spent much time on the US forums in a long long while.
Looks like a neat mod though.
 
It's not about finding one that fits correctly, it's about which one performs the best in a given rifle.

In Gus's write up, he took all the pistons from his shooting teams rifles and swapped them rifle to rifle. I won't try and quote the guy or anything, I'm sure his article exists out there in cyberspace.
There were tangeable results and a lesson to be learned in reading Gus's comments on swapping pistons to find "the one".
 
Is there a way to know witch piston is best without douing accuracy testing at the range? Is there a clearance spec that could tell the tail? Would it be more weight or total gas flow?

Very interesting tread.
 
I think, what many of you guys are thinking is that piston swapping is a Magical tweek that will turn a stock rifle into a one hole lazer beam. It is not, the rifles that Gus performed this proof of concept on were full blown USMC Match tuned rifles where every iota of accuracy is squeezed out too make them perform on a National stage. Like everything accuracy oriented with the M-gun its incremental, every tweek has too work in unison with the other.
 
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