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This is a discussion on Piston chat.. within the Art Luppino forums, part of the Gun Professionals category; The best way to start this Thread is to admit nobody really knows.. Some of the things that are known resulted from testing years ago, ...


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Old December 10th, 2016, 07:23 AM   #1
Lifer
 
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Piston chat..

The best way to start this Thread is to admit nobody really knows..

Some of the things that are known resulted from testing years ago, Sharing the test results may provide answers or may bring even more questions

The tests were conducted in an attempt to find a common factor between the Matched conditioned M14's that displayed a high degree of accuracy across the course opposed to the Matched M14's that displayed a lesser degree of accuracy.

These M14's were built using the same materials and methods, tested with the same ammunition by top shooters. Tests were conducted at the 300 yard line, prone slow fire with a mag of two and eight.

Given, there are too many factors, not all of which could be investigated, the results in these limited tests indicated an interesting thing about the gas systems. It is this result I hope to share.

All the M14's that preformed well had free flowing pistons. Free folowing meaning the piston would fall very rapidly when the muzzzle was elevate with a cool barrel, somewhat slower when heated after a string of 10 was fired. The less accurate performing M14's had a slow falling pistons, sometimes called vacuum drag when tilted with a cool barrel, with a heated barrel some pistons did not fall
unless the rifle was snapped downward.

If you are not pleased with the accuracy of you rifle, or building a new one, it is well advised to start with a new or as close to new cylinder as possible. Select a piston that falls freely. These two parts are not too expensive, pistons are reasonalble, so buy several.. Buy only USGI gas system parts... Art

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Old December 10th, 2016, 07:43 AM   #2
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Sadly Uncle Sam is no longer making parts for himself or us. That being said I like the Sadlack tin coated gas pistons. I once heard that the plated pistons cause more wear. I fail to see how if the clearance / tolerance is correct but I do like the easy clean up.

All my guns have smooth moving pistons so things are working right.

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Old December 10th, 2016, 08:20 AM   #3
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Interesting thread Art. I alway check my piston drag after I clean it but I've never checked it in the field after it's been fired. I'll have to check that next time out to see the difference.

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Old December 10th, 2016, 08:22 AM   #4
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How does the M25 mod and the vent hole in the gas plug come into play? These mods, along with a vented gas piston, create a system that has no vacuum drag.

Tony.

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Old December 10th, 2016, 08:54 AM   #5
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Good question Tony

Hello Tony,,

The venting of gas plugs is not new, it was well tested years ago for the purpose of using heavy bullets for long range. The results were negitive and the project discontinued. Venting reduces the vacuum, which is not the reason for a slow piston, the reason would more likey be a piston too large in Dia. for that cylinder, or an out of spec cylinder, maybe both.

I think we tend to forget when the cylinder and piston heat up, they expand, there were many that belived that condition is the cause of the dreaded cold bore shot in a M14/M1A. As for the cold bore shot from a bolt rifle, all the top bolt rifles I fired did not produce an out of group cold bore shot, none of them.. You may have had a different experience..

Keep up the good work, we all value your reports.. Art

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Old December 10th, 2016, 10:11 AM   #6
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Quote:
Originally Posted by art luppino View Post
Buy only USGI gas system parts...
In light of the rest of your explanation, this last bit sounds like superstition. Math, science, math, science ... brand loyalty.

I understand that the gov't spec'd the parts and enforced a rigorous QA, but that isn't to say a modern manufacturer couldn't replicate or improve the quality of the product.

What am I missing? Why original USGI pistons and not SEI chromed pistons, Bula or LRB nitrided pistions, or Sadlak TiN pistons if they pass the tilt test (cold and warm)?

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Old December 10th, 2016, 12:47 PM   #7
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Good point

Re-reading my Post I find no mention that a commercial Company can not make parts to spec..
However,, being able to and doing so are are two different things.

Using USGI new gas system parts offers the best opportunity to build a sound trouble free M1A or M1 Garand. Further more on this subject, all the M1A parts that have a moving contact relationship should be USGI. If you just require that the rifle works commercial parts are availble.. Art

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Old December 10th, 2016, 01:48 PM   #8
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I hope I did not come across as obstreperous. I'm just trying to wrap my head around this stuff and assemble a rifle I can be proud of. Is the following a fair summary of your explanation?

1) We don't know everything about why some pistons work and some don't.
2) The relative ease with which a piston falls in tilt tests before and after a rifle has been fired provides some predictive data on the precision of the rifle, at least insofar as the gas cylinder assembly affects precision.
3) At this time, USGI pistons (as a known commodity) should be favored over commercially produced pistons, the comparative quality and consistency of which ranges from unfavorable to unknown.

May I conclude that while some commercial pistons provide distinct advantages for cleaning, there is a measurable trade-off in precision? Or is the data set not large enough to know about the precision consistency of particular commercial manufacturers? I am thinking about Bula, which I believe has secured government contracts for a handful of M14 parts. Should we resist attributing USGI quality to their range of parts beyond those specifically under gov't contract?

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Old December 10th, 2016, 02:06 PM   #9
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The original piston in my Nelson built Supermatch moves slower like the mentioned vacuum drag speed. Still shoots extremely well.

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Old December 10th, 2016, 02:40 PM   #10
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ArtL, thanks for keeping the discussion going about the mysteries of an accurate M14. My piston falls "ceremoniously" with gas plug installed, but drops like a rock with gas plug removed. It's my guess that there is a slight vacuum, not an interference, that slows the piston drop.

Do you recall any evaluation of vented gas plugs with 155 or 168 grain bullets? Has anyone evaluated the consistency of lowerband contact with stock ferrule? Or compared accuracy versus various draw forces?

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Old December 10th, 2016, 03:36 PM   #11
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An attempt to answer.

Quote:
Originally Posted by Pennamite View Post
I hope I did not come across as obstreperous. I'm just trying to wrap my head around this stuff and assemble a rifle I can be proud of. Is the following a fair summary of your explanation?

1) We don't know everything about why some pistons work and some don't.
2) The relative ease with which a piston falls in tilt tests before and after a rifle has been fired provides some predictive data on the precision of the rifle, at least insofar as the gas cylinder assembly affects precision.
3) At this time, USGI pistons (as a known commodity) should be favored over commercially produced pistons, the comparative quality and consistency of which ranges from unfavorable to unknown.

May I conclude that while some commercial pistons provide distinct advantages for cleaning, there is a measurable trade-off in precision? Or is the data set not large enough to know about the precision consistency of particular commercial manufacturers? I am thinking about Bula, which I believe has secured government contracts for a handful of M14 parts. Should we resist attributing USGI quality to their range of parts beyond those specifically under gov't contract?


I do not feel you have been loud and unruly'

After this test was conducted the results indicated free flowing pistons out performed non free flowing pistons in across the course Match M14's, it was not detrmined as to why..

Predictive data, I do not know, it maybe a good place to start in my opinion..

I favor USGI pistons and cylinders.

Cleaning was not consider a factor. You are free to resist what ever you choose.

Thank you for you interesting questions. Art

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Old December 10th, 2016, 04:26 PM   #12
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Quote:
Originally Posted by tonyben View Post
How does the M25 mod and the vent hole in the gas plug come into play? These mods, along with a vented gas piston, create a system that has no vacuum drag.

Tony.
Tony the M25 mod is really just a tail pipe in the rear of the cylinder for the carbon too clear out of, its not meant for venting any real amount of pressure..

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Old December 10th, 2016, 05:18 PM   #13
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A few answers, maybe..

Quote:
Originally Posted by shooter86314 View Post
ArtL, thanks for keeping the discussion going about the mysteries of an accurate M14. My piston falls "ceremoniously" with gas plug installed, but drops like a rock with gas plug removed. It's my guess that there is a slight vacuum, not an interference, that slows the piston drop.

Do you recall any evaluation of vented gas plugs with 155 or 168 grain bullets? Has anyone evaluated the consistency of lowerband contact with stock ferrule? Or compared accuracy versus various draw forces?
It is not uncommon to have a slower pistion fall with the plug in. A plug installed tight puts a good deal of pressure on the face of the cylinder, this pressuer can and does often disturb the gas cylinder causing slight miss -alignment issues tis is reflected in the piston flow.. Alsso a cylinder lock drqwn up too tight can cause the cylinder to crimp, that's the best word I can find, cople these two together and bigber problems start to show up.

Fit you lock, if using shims, to finger tight at no more then 5:00, torque the plug to around 150 to 160 inch lbs.. Things should get better after a box or so rounds are fired..


Using index marks is not a good method, but better than no method...''

Never found vented plugs to be of any help accuracy wise. In my opinion they are gimmicks.. Art

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Old December 10th, 2016, 06:00 PM   #14
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I realize that the precise details about the testing are probably not available, but it would be interesting to know -

1) Did ALL of the rifles with 'fast' pistons perform better than ALL the rifles with 'slow' pistons?

2) Were any piston changes done to test 'slow' pistons in rifles that formerly had 'fast' ones? And the other way too.

And who knows, maybe it wasn't the pistons at all - maybe it was something with the gas cylinders instead. e.g. having the direction of the piston's movement be on the same axis as the oprod. Or perhaps the 'bore' of the cylinders being more 'straight' and uniform.

I accept the results of the test for what they are, but it's sometimes difficult to determine WHAT actually caused the results.

Jay Kosta
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Old December 10th, 2016, 06:24 PM   #15
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Quote:
Originally Posted by JayKosta View Post
I realize that the precise details about the testing are probably not available, but it would be interesting to know -

1) Did ALL of the rifles with 'fast' pistons perform better than ALL the rifles with 'slow' pistons?

2) Were any piston changes done to test 'slow' pistons in rifles that formerly had 'fast' ones? And the other way too.

And who knows, maybe it wasn't the pistons at all - maybe it was something with the gas cylinders instead. e.g. having the direction of the piston's movement be on the same axis as the oprod. Or perhaps the 'bore' of the cylinders being more 'straight' and uniform.

I accept the results of the test for what they are, but it's sometimes difficult to determine WHAT actually caused the results.

Jay Kosta
Endwell NY USA
Well said!!

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