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Piston = Accuracy?

This is a discussion on Piston = Accuracy? within the Accuracy forums, part of the M14 M1A Forum category; There exists a relationship between the piston and the cylinder walls, the best accuracy happens when this relationship is at point X. Nobody knows what ...


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Old March 15th, 2017, 09:48 AM   #16
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Once more into the----

There exists a relationship between the piston and the cylinder walls, the best accuracy happens when this relationship is at point X. Nobody knows what or where point X is.. By piston change-out the best relationship between the pistions on hand and cyl walls can be found, sometimes.

There is also two another factors. That's the air in the bore being forced forward rapidly, it expands and acts on the awaiting pistion and flash suppressor.

Time for a BIG RED.. Art

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Old March 15th, 2017, 11:54 AM   #17
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Question

Quote:
Originally Posted by art luppino View Post
There exists a relationship between the piston and the cylinder walls, the best accuracy happens when this relationship is at point X. Nobody knows what or where point X is.. By piston change-out the best relationship between the pistions on hand and cyl walls can be found, sometimes.

There is also two another factors. That's the air in the bore being forced forward rapidly, it expands and acts on the awaiting pistion and flash suppressor.

Time for a BIG RED.. Art

Art, I understand what your saying but I also have a counter idea.... A grooved piston would allow more air too slip past, then the weight of the op-rod and the strength of the return spring pushing against the piston would still be the same. I'm not saying there is zero movement, but less than is the norm.

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Old March 15th, 2017, 12:16 PM   #18
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As i see it, the air in the tube would take the path of least resistance. Get pushed out the front of the barrell. The gass behind the round, once it seals in the barrell, may escape through the grooves but still will go out the end of the barrell easier than diving through the gas port. As the round passes over the gas port the resistance of the seal between the bullet and barrel will send the gas douwn the gas port. Short of pulling the shot in that last millisecond the piston has no influence to this point. Its an oblect not in motion.....i think

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Old March 15th, 2017, 12:58 PM   #19
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I've been giving this piston business some thought. We'd have to get the engineering design notes but I'm certain field functionality and reliability were the prime goals with accuracy not a factor as long as the overall rifle accuracy metric was achieved.

What happens when the piston returns to its "A" position?
Is it placed against the gas plug and kept there by pressure from the spring?




Quote:
Originally Posted by Ted Brown View Post
It's interesting and still baffles me somewhat that a piston can effect accuracy. In reality, the bullet is out of the barrel before the piston starts to move. The only thing I can figure is that piston movement effects the harmonics of the barrel as it vibrates and settles back to rest after the shot. This may have an effect on how the rifle moves during the next firing cycle. With a gas operated rifle accuracy is dependent on consistency and some piston/gas cylinder combinations may work better than others. Note that there is not really a "match" piston. They are all basically the same. The longitudinal groove was included in an attempt to ease up some of the forces on the rifle's action during firing. it has the added benefit of keeping pressures down in the gas system when shooting heavier bullets, however the M14 can handle bullet weights up to 185 grains without problems. The grooved pistons also can contribute to short cycling which we don't want to happen. We tried them back in the early 80's and found no benefit in our NM rifles so they were replaced with standard pistons after only about a season of use.

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Old March 15th, 2017, 01:52 PM   #20
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That may be over simplifying it. The M14 is a creature of many moving parts and accuracy is dependent on how those moving parts relate to one another. Throughout the firing cycle there are numerous interactions that effect the rifles harmonics, not just the barrel harmonics. It would fill a book to try and explain it. The relationship of the piston is but one very small part of a larger picture. It's contribution to accuracy is not all that significant, but it makes a difference to Master Class shooters.

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Old March 16th, 2017, 10:27 PM   #21
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All is great! Keep shootin x ring and don't worry! Ya if the wheel isn't Broken theory! Just have fun eh!

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Old March 17th, 2017, 03:23 AM   #22
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Quote:
Originally Posted by shooter86314 View Post
tedbrown said:

lysander said:

It's interesting to me that this difference of opinion still exists.

I have read some anecdotal reports that the oprod moves before the bullet leaves the barrel, but I have seen only one report of reliable testing, which is quoted occasionally on this forum: Springfield Armory Technical Note SA-TN11-1094 dated 16 Dec 1957

Here is one link to it, posted by different in 2009:

Timing Analysis of Unlocking Cycle for M1 and M14

Just last night, I started searching the SA Museum site for that photo test. I am still looking.

Several weeks ago, a TV pundit was discussing something political. He said, the plural of anecdote is not data.
I posted some graphs from Technical Report SA-TR11-2610, Gas Systems - Caliber .30, T44 Rifle.

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Old March 17th, 2017, 06:00 AM   #23
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OP, Gus Fisher has a great post if you do a search on the impact of Gas Pistons and accuracy. Basically what he writes is that when he was the armorer for USMC rifle team they discovered that certain pistons "fit" with a particular rifle. They would take 5 pistons (not necessarily new) and try them in a rifle changing no other variables (e.g. torque kept the same, etc.). One piston of the five, for example, would produce noticeably tighter groups.

As Ted mentioned (and others) no one knows why. It is just a fascinating platform...so many moving parts and so many inputs to accuracy (piston, stock, headspace, sights, etc.) but when you get it right it is so sweet....

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Old March 26th, 2017, 08:21 AM   #24
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I spent the better part of Friday and Saturday testing, among other things, different gas pistons in my already decently-tuned and set up National Match, Socom and Scout. All three are in tightly fitted Boyds stocks and of course the NM is bedded. I used a 7x scope on all three guns, and fired groups at both 50 and 100 yards, using Fiocchi 150gr fmj, AE 168 gr 7.62x51, Federal Gold Match, Black Hills 168 Match, and Hornady Match 168 BTHP.

In my limited samplings of these recent-production, fresh, newer Springfield commercial guns, I came to the following initial conclusions from my own little tests, which only apply to these three specific rifles:

1) If you torque the gas plug to less than 15 ft lbs, it can begin to loosen up under fire. I torqued all gas plugs to about 18 ft lbs with a high quality torque wrench, for my comparisons, just to be consistent. The plugs stayed put. I didn't try heavier torque than that.

2) I used the several different ammo loads I had with me, all 168 grain except the Fiocchi 150gr, with each piston and each rifle. It appears to be a combination of the rifle itself, the particular load, AND the gas piston, working somehow in harmony. When you land on a winning combo, it is more than obvious, and it is consistent.

3) None of these three newer guns showed any significant improvement over the commercial stock gas piston they came with, when I tried the NOS GI gas piston I had with me. In fact, my Scout consistently grouped a little worse with the GI piston across the board with all ammo tried.

4) None of my three guns shot the Fiocchi 150 grain ammo worth a spit, not even my National Match. In fact, the NM shot the 150 grain ammo the worst of the three rifles. These new Springfields were built around 168 grain ammo, clearly, and it's all the barrels want any part of. All three guns also preferred slightly faster/hotter ammo over slightly slower ammo.

5) I saw a marked improvement in both my National Match and my Scout, when installing the Sadlak TiN match gas piston (the non-grooved models, since I did not have a grooved model to try). I have NO idea why. I had two of these Sadlak TiN pistons, and using the Hornady BTHP in particular, groups consistently were more than 20% tighter than using the commercial factory pistons that came with the guns, especially in the Nat Match. The Black Hills and AE 7.62 also showed much better groups with the Sadlak piston, in the Scout. Going back to the stock gas piston, groups would open right back up, especially on the National Match.....I though that thing already "came" with a NM gas setup??? Meh!

6) The Socom I have is very accurate after its tightly fitted Boyds stock and many other mods, and it showed no real preference for any Gas Piston with most of the ammo used, except that it did shoot the AE better consistently with the Sadlak TiN. But with its favorite Hornady BTHP load, it shot equally well with the Sadlak or its own stock piston.

I was confident enough in my observations, after many rounds downrange and a phenomenal weekend blasting away with these incredible rifles in a perfect 78 degrees, that I left the Sadlak pistons in the Scout and the Nat Match, and I was perfectly fine leaving the factory gas piston in the Socom. Especially in the Nat Match, the Sadlak TiN piston (I tried both Sadlak pistons I had in it, and they gave about the same result) was a worthy and quite noticeable upgrade to an already great-shooting rifle.

I will speculate that if I had used different weights or brands of ammo, and if I had not already carefully fitted and tuned these three rifles, including shimming the gas systems, clearancing the handguards/ferrules/op rods/stocks etc, some of my conclusions about the pistons might have been different, or might have been obscured by other factors. With the rifles otherwise already reasonably well set-up, I did experience differing and quantifiable results with different gas pistons. And based on my Socom, I can easily see how your mileage may vary. If the Socom was my only rifle, and the black hills was the only ammo I ran through it, I would have to conclude that the Sadlak piston made absolutely no difference over the stock commercial piston that came with the gun. Yet, right now, you couldn't FORCE me to put the stock gas pistons back in my Scout and NM.

You just have to experiment for yourself with your own gun, your own chosen ammo/loads, the proper tools to do some swapping, and a few different pistons.

After all that, I still have to try these adjustable Schuster gas plugs I picked up LOL!!! That's next on the list, to see if groups will change at all by tuning the gas plugs themselves to fine-tune the recoil impulse to the load....These guns have tons of mystery voodoo and mojo, I love it!


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Old March 27th, 2017, 05:28 PM   #25
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I have a lot of targets from the weekend, but here is an example of what I saw repeatedly with my Nat Match JUST when going from the stock SAI gas piston to the Sadlak gas piston, no other changes......I know these are mostly three-round groups but I was trying to conserve ammo initially so I could get through all the testing with all three rifles and four different gas pistons. Later five-round groups from the Nat Match confirmed results, and by the end of the day, I could keep almost all rounds touching in five-round groups at 50 yards with the Sadlak piston, consistently. I couldn't come close to doing that with the stock gas piston using the exact same ammo. Hence, the two Sadlak TiN Gas Pistons I had brought with me for these tests now live permanently in the Nat Match and Scout Squad, for this reason.......


Sadlak piston:






and...putting the stock gas piston back in, not so much:





And NO, before you ask, I don't work for Sadlak, HA HA!!! And, I bought these pistons with my own green beans, just to experiment with for myself, thinking the whole issue was over-hyped. Frankly, I was rooting for the USGI NOS gas piston. Nope, not in these guns. I still have a hard time believing the results I got, myself, and I was there shooting the guns and swapping the pistons, in front of about 20 other folks at the rifle range for two days, some of whom probably thought I was nuts. I'm still completely baffled at WHY the gas pistons can have this much of an effect on groups, or in some cases no effect at all, and why it is mostly on certain ammo rather than others, but I ain't complaining about what I wound up with!!!

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Last edited by MGSchindel; March 27th, 2017 at 05:49 PM.
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Old March 27th, 2017, 07:02 PM   #26
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I've had similar results with my Sadlak Pistons out performing USGI or SAI Pistons. .
I know many will swear by USGI Pistons getting better performance but I haven't seen it in my rifles. I still need to try my Bula nitrated Pistons to see how they compare.

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Old March 27th, 2017, 07:16 PM   #27
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Quote:
Originally Posted by Capona View Post
I've had similar results with my Sadlak Pistons out performing USGI or SAI Pistons. .
I know many will swear by USGI Pistons getting better performance but I haven't seen it in my rifles. I still need to try my Bula nitrated Pistons to see how they compare.
I'm getting the sense that the original USGI pistons, no surprise, will run best most of the time in guns sporting an original USGI gas system. I have the sneaking suspicion that the specs to which the Sadlak gas pistons are made just happen to work better with whatever specification the current SAI gas systems are made to. Are the Sadlak pistons, on average, slightly bigger (or smaller) in diameter, or shorter or longer, than the average USGI gas pistons? Has anyone quantified this by measuring a decent sample of both? Are the USGI and SAI gas cylinders made to ever-so-slightly different specs? I'm just curious.....

Please do indicate how your guns respond to the Bula pistons, if you get a chance to tinker!


Last edited by MGSchindel; March 27th, 2017 at 07:29 PM.
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