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Groved or Slotted Pistons

This is a discussion on Groved or Slotted Pistons within the Art Luppino forums, part of the Gun Professionals category; Interesting thing about these modified pistons, as far as I know nobody seems to have the reason for the Mod.. Like everyone else, I have ...


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Old December 12th, 2016, 02:35 PM   #1
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Groved or Slotted Pistons

Interesting thing about these modified pistons, as far as I know nobody seems to have the reason for the Mod.. Like everyone else, I have heard a fair number of reasons for the grove/slot, but if you question the party advancing their explanation they have no facts to offer. Of coures they charge you more for one.. Toss in a platted pistion and you have made someone happy..

The best explanation came from a retired Marine that spend his career in the RTE shop. He recalls their first apperance, they cut the slots my hand, the grove wondered all over the place, much like the one Banbam owns, He retrieved out of my trash bucket.

The Mariine's junked the mod to the piston, claiming it did nothing to improve the M14's. If you own and run a slotted piston and like it, who needs an explanation. Personally I believe it is an ongoing exercise in expiration.. Cranky Art

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Old December 12th, 2016, 02:49 PM   #2
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Yep, right in the same bin with the buffer thingy and the tack driver.

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Old December 12th, 2016, 03:24 PM   #3
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I'm still not sure which direction the gas is moving in the groove.

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Old December 12th, 2016, 03:40 PM   #4
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Put one grooved/plated in my LRB and even though the GI worked fine, the new one seems to slide back and forth much easier(tilt test) and as far as shooting can see no difference in performance. Keep the original in my spares kit for possible future use along with spare firing pin, extractor, spring kit, and of course the two drill bits and gas plug wrench. Rifle has SA GI trigger group and most likely in the near future will buy me a complete GI trigger group for a spare as well.

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Old December 12th, 2016, 04:13 PM   #5
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I realize now my strategy of using what was already in my rifle all these years was a wise one.

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Old December 12th, 2016, 04:17 PM   #6
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Way back when... the National Guard tried grooved piston in our M14's thinking they would ease cycling velocity which would make the rifles run easier and reduce recoil. Slotted pistons were also thought to allow the piston to slide back and forth faster than an unslotted piston which may have had some effect in the operators confidence that his rifle was running to it's best ability... I think it had something to do with the operators head space... Anyway, we dropped them after about one season of use and never looked back.

I do think they may have some advantage when shooting the M118LR round as it seems to run at slightly higher chamber pressure. But again, it has more to do with the operator's head space.

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Old December 12th, 2016, 04:40 PM   #7
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Disclaimer: I don't know jack!!!

But as I was hoping to improve the accuracy of my less than impressive, recently purchased, M1A loaded, I bought one of the grooved pistons, along with a NM spring guide, and a CS spring. I don't know if it makes a difference or not. The spring guide certainly makes the action feel smoother.

I had to call Sadlak, as no one had the grooved piston in stock, and here's the thing. The guy asked me if I was firing suppressed. He said they were selling a lot of them to customers who were looking to fire suppressed......

Thats all I got.

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Old December 12th, 2016, 04:41 PM   #8
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Who am I to disagree with guys like Cranky Art and Ted Brown, but it has been my understanding that the groove was intended to relieve the higher port pressures when using heavier bullets, slower powders, etc. and was meant to ease the pounding on the gas system. Much like the Schuester gas plug. Not necessarily improve accuracy...
Correct me if I'm wrong.

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Old December 12th, 2016, 05:13 PM   #9
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I don't see how a grooved piston can relieve port pressure. While the volume of the groove allows for that much more gas to enter the cylinder, the gas isn't escaping the cylinder thru an additional port as it does with the Schuster plug. Schuster has tested their port and states that it lowers pressure by 2k psi.

When gas enters a grooved piston, the groove is at a dead end against the rear edge of the gas plug, so there is no place for the gas to bleed off to. Once the piston begins rearward movement, the end of the groove will be exposed and gas can travel back towards the barrel port. How much gas can be bled off down the groove and back into the barrel before the rear of the cylinder clears the bottom port is a mystery to me. I suppose every little bit helps.

The groove does help break the vacuum seal and allows for easier piston movement during a tilt test.

Someone correct me if this doesn't make any sense.

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Old December 12th, 2016, 05:52 PM   #10
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HEY! I bought one and put it in early on and to this day wonder IF I could have shot better with my original one...

DO know I had to up my powder charge by .5 gr to cycle like before... Maybe it is a game by the powder companies to sell more powder!?

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Old December 12th, 2016, 06:26 PM   #11
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I'm nobody, but the explanation that Old Sarge makes is the one I've read most frequently. The groove would make a path for gas to escape out past the half-round portion of the cylinder. While the groove isn't all that big, it probably represents a path at least equal to 10% of the barrel port hole, if not bigger.

The half round part of the piston has lots of clearance with the mating surfaces of the gas cylinder and could easily pass a lot of gas.

I see no direct correlation with accuracy. Simply a way to expand the operating envelope.

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Old December 12th, 2016, 06:41 PM   #12
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If gas is escaping towards the piston tail, then it is slowing down the rearward movement of the piston. There would now be additional air/gas for the cylinder body to compress out of the rear of the cylinder.

It would also be dumping additional carbon into the stock, which I would find distressing in a bedded rifle that only gets taken apart periodically. It wouldn't matter much in an open stock like a Sage.

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Old December 12th, 2016, 06:42 PM   #13
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Quote:
Originally Posted by art luppino View Post
Interesting thing about these modified pistons, as far as I know nobody seems to have the reason for the Mod.. Like everyone else, I have heard a fair number of reasons for the grove/slot, but if you question the party advancing their explanation they have no facts to offer. Of coures they charge you more for one.. Toss in a platted pistion and you have made someone happy..

The best explanation came from a retired Marine that spend his career in the RTE shop. He recalls their first apperance, they cut the slots my hand, the grove wondered all over the place, much like the one Banbam owns, He retrieved out of my trash bucket.

The Mariine's junked the mod to the piston, claiming it did nothing to improve the M14's. If you own and run a slotted piston and like it, who needs an explanation. Personally I believe it is an ongoing exercise in expiration.. Cranky Art
It sort'a defeats the purpose of the gas cut-off feature of the piston . . . as it allows gas to enter the piston (now, from the front end of the groove) even after the gas ports move out of line.

The CORRECT solution to reduce the gas pressure inside the piston, which it how you would reduce the cyclic rate, is to 1) move the port rearward, and thus reduce the time the gas ports are aligned, or 2) reduce the size of the hole in the piston. Neither of which can be done to a stock piston.

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Old December 12th, 2016, 07:34 PM   #14
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I thought it was like the "old" days when you shot some one you would "notch" your piston.

No, actually its for use with the heavier bullets weights to reduce the strain on the gas system (Op-Rod) and the resultant extra speed of the the oprod when firing the 168's or 172's bullets. I used to shoot the 168 Grain GM M2 AP out to 600 meters and then switch to the 172 Grain GM 9 Degree Boat tail M1 Type for 700, 800, 900 and 1000 meters.
But later (mid 1980's)on I just used the 168 Grain 13 Degree Boat tail Sierra Match kings for everything.
The flat base bullets (M2 - AP) really work well at the shorter distances, but tend to "spin off" past that 600 yard mark.

This all really often goes hand in hand with "rip-off" of the cartridge-case rims by the extractor, as the op rod, and therefore the bolt, are cycling too fast with the higher pressures of the larger bullets. (especially on the hotter hand loads). The notching of the piston is just an attempt to slow down the unlocking of the action.

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Old December 12th, 2016, 11:05 PM   #15
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Quote:
Originally Posted by art luppino View Post
Interesting thing about these modified pistons, as far as I know nobody seems to have the reason for the Mod.. Like everyone else, I have heard a fair number of reasons for the grove/slot, but if you question the party advancing their explanation they have no facts to offer. Of coures they charge you more for one.. Toss in a platted pistion and you have made someone happy..

The best explanation came from a retired Marine that spend his career in the RTE shop. He recalls their first apperance, they cut the slots my hand, the grove wondered all over the place, much like the one Banbam owns, He retrieved out of my trash bucket.

The Mariine's junked the mod to the piston, claiming it did nothing to improve the M14's. If you own and run a slotted piston and like it, who needs an explanation. Personally I believe it is an ongoing exercise in expiration.. Cranky Art
Art,

Are you talking about this jewel? This priceless unit is the enabler to the best shooting M1A that came from your shop... It's for sale and you have the exclusive right to buy it.
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