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panabax

USA Made M4 Gas Piston Prototype

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Just thought you might want to see the gas piston coming into being. This picture is the work in progress prototype next to the factory original. I still need to make the radial cuts in the gas rings and then heat treat. Then, I need to make one more just like this one. The shame is that these would be super easy to turn on a CNC lathe and pretty cheap too, but the radial cuts add a lot of complexity to the CNC manufacturing.

 

Perhaps if these work well, I will order a lot of pistons without the radial cuts (cheap to manufacture) and then do the radial cuts by hand. Might not be too bad. The lathe work on a manual lathe is a real time hog. I have many hours in this one piston.

 

m4_piston.jpg

 

Panabax

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Why did you deviate from the original dimensions of the piston?

 

You're kidding, right? You should see me with my micrometers in hand trying to measure the distances on that damn thing and then trying to recreate it on my miniture lathe. The groove between the two rings at the end is only .055" There is not much room in there for a tool. In other words, any variation in the dimensions is purely non-intentional. However, I suspect the most critical dimensions will be diameter of gas rings and length of piston. Just a guess.

 

I was just glad that it is clearly recognizable as an M4 piston. I will keep you posted as the project progresses.

 

Panabax

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You're kidding, right? You should see me with my micrometers in hand trying to measure the distances on that damn thing and then trying to recreate it on my miniture lathe. The groove between the two rings at the end is only .055" There is not much room in there for a tool. In other words, any variation in the dimensions is purely non-intentional. However, I suspect the most critical dimensions will be diameter of gas rings and length of piston. Just a guess.

 

I was just glad that it is clearly recognizable as an M4 piston. I will keep you posted as the project progresses.

 

Panabax

 

I can eye-ball the picture and tell you that they aren't the same. Not that it is critical that they be the same, but I figure they were designed with certain angles, etc. for a reason. It begs the question from others: "what else is different?"

 

Being as this is a highly stressed part, material and heat-treat are going to be HUGE. THen you will need to test the design pretty hard to ensure that it is durible. Just a lot of reliability headaches/worries with this part.

 

20sj11c.jpg

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damn UNO, go easy on the brutha!! all i can say at this point is, at least PANABAX is trying to come up with parts to help with the stupid laws/rules governing our nelli m4's. and heck, he sure looks to be a pretty talented guy from the pics. that said, he also at least is doing a better job than some of the bigger tactical aftermarket parts companies that are'nt even doing sh-t trying to make ANYTHING!! thats at least anything worth us actually wanting to buy and put on our nellis!!;) there isnt even a decent foregrip made in the USA yet that everyone just has to have for the m4. and that seems like it would be the easiest part to recreate!! tubes and sidearmor rails, thats it, thats all that is any good so far!! i have a feeling panabax will perfect this piston if all goes well. and when he does, "whos the BEEEACH now?":D

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Fair enough on the eye-ball. If you get take your mics to it you will find other deviations that are harder to see. However, the diameters of the rings is right on and it fits perfectly. I will cut the radial grooves, heat treat it and see if I can break it. If the prototype works, I am already modeling a cad version for a small production run to get a more precise product.

 

The 3d model is below. I will kepp you posted.

 

Panabax

 

m4_piston.bmp

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Looks like a good start. I agree, you'll want more material on the over travel stop. It, and the face that impinges on the bolt carrier group are the highest stress areas on the unit. The over travel stop causes the piston to reverberate upon impact. This leads to some sheering forces along the thinner portion of the shaft since it is relatively unsupported.

 

Have you checked the weight of the two to see if they're in the relative area of each other?

 

Any thoughts on if weight differences would affect the action?

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Have you checked the weight of the two to see if they're in the relative area of each other?

 

Any thoughts on if weight differences would affect the action?

 

Minor weight differences shouldn't have a significant impact on the action. If it is too heavy, it might be tougher to move with the force of the expanding gasses; but there would have to be significant deviation for it to affect the reliability of the action. The diameter of the gas rings will have much more effect on this than the weight.

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damn UNO, go easy on the brutha!! all i can say at this point is, at least PANABAX is trying to come up with parts to help with the stupid laws/rules governing our nelli m4's. and heck, he sure looks to be a pretty talented guy from the pics. that said, he also at least is doing a better job than some of the bigger tactical aftermarket parts companies that are'nt even doing sh-t trying to make ANYTHING!! thats at least anything worth us actually wanting to buy and put on our nellis!!;) there isnt even a decent foregrip made in the USA yet that everyone just has to have for the m4. and that seems like it would be the easiest part to recreate!! tubes and sidearmor rails, thats it, thats all that is any good so far!! i have a feeling panabax will perfect this piston if all goes well. and when he does, "whos the BEEEACH now?":D

 

Trigger/sear would have been a lot easier and are not subjected to nearly as harsh a life as the piston. I agree that it's nice, but I would have trouble trusting something that requires a very specific hardness and toughness and that has been tested by a couple dozen people and if broken, would prevent the weapon from cycling. Even Benelli had trouble with the operating system initially with their 4-port design, etc. If that can slip through testing at Benelli...

 

I think it's good that this is being made and hate to detract from it, but I personally would not buy it until a LOT of testing has been done.

 

Just my .02

Edited by Unobtanium

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Trigger/sear would have been a lot easier and are not subjected to nearly as harsh a life as the piston. I agree that it's nice, but I would have trouble trusting something that requires a very specific hardness and toughness and that has been tested by a couple dozen people and if broken, would prevent the weapon from cycling. Even Benelli had trouble with the operating system initially with their 4-port design, etc. If that can slip through testing at Benelli...

 

I think it's good that this is being made and hate to detract from it, but I personally would not buy it until a LOT of testing has been done.

 

Just my .02

yeah, but think about it UNO. if you did buy a set made, you could try and beat the sh-t out of them yourself!!;)

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yeah, but think about it UNO. if you did buy a set made, you could try and beat the sh-t out of them yourself!!;)

 

Or I could keep my OEM ones and not worry about it.

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Or I could keep my OEM ones and not worry about it.

yeah but im not er,um, hum,hum 922 um er compliant with the way my m4 is set up right now. but would like to be someday just for sh-ts and giggles!!;) and U.S. made pistons would fix that, cause i still havent seen or wanted any of the after market handguards yet!!:o

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yeah but im not er,um, hum,hum 922 um er compliant with the way my m4 is set up right now. but would like to be someday just for sh-ts and giggles!!;) and U.S. made pistons would fix that, cause i still havent seen or wanted any of the after market handguards yet!!:o

 

 

922r compliancy is right after buying a Prius on my feel-good list.

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Could always have your factory pistons engraved MADE IN USA and NP3 coat them if you're real worried about it.

 

I agree. You could also take a wood-burner to the OEM forearm and do the same thing and stipple it. Would be kinda cool.

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922r compliancy is right after buying a Prius on my feel-good list.

L'dMAO again!!:D and F#%K the prius!!i'd drive a tank to work if i could afford one!!;) no more traffic either. just run them over or just blow them up!!

Edited by texas skeeter

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Nice job Panabax! Thanks for attempting to tackle this.

 

No problem. I have a degree in Mechanical Engineering and a machine shop in my garage so it is more hobby than altruism. I am going to machine another prototype by hand and use the prototypes to test various hardness/toughness combinations. The material is 15-5 stainless which is a precipitation hardening material. That means you heat to a time and temp for a specific hardness. No quenching, no tempering. It is much easier to hit targets with than with more conventional alloys. The strength and toughness characteristics of this material are very good. It is used extensively in the aerospace industry for mission critical parts. I am sure it is very much up to the fairly simple task of transmitting energy from the barrel to the bolt face.

 

I think I will apply different heat treatments to the two pistons, one softer one harder, and see if one bends or breaks.

 

Really, you should see some of the materials I have seen used for semi-auto rifle pistons. I have an original Rhino M-16 piston conversion and the piston is quite simply 1/8" drill rod. It actually worked quite well, although it has long since been retired to the old gun parts pile.

 

Clearly, the only reason for these pistons would be 922r compliance and, for that reason, it is a dumb project. Still, I try to do what I can to abide by all of the laws that govern our society, even the stupid ones.

 

I will post pictures when I get the other made and then, to the range. Now that will be the best part, trying to break them.

 

Panabax

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922r compliancy is right after buying a Prius on my feel-good list.

 

Same.

 

However I still support the development of aftermarket Benelli parts ... and you're making some pretty cool stuff thus far Panabax.

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Properties of 15-5 PH Stainless Steel

15Cr-5Ni is a martensitic precipitation hardening stainless steel offering high strength and hardness along with excellent corrosion resistance. Generally similar to Custom 630 (17Cr-4Ni) in composition and properties, 15Cr-5Ni is chemically balanced to eliminate all but trace amounts of delta ferrite, thus providing superior transverse toughness and ductility plus a higher degree of forgeability.

15Cr-5Ni has fabrication characteristics similar to those of other precipitation hardening stainlesses, and can be age-hardened by a single-step, low temperature treatment.

It has been used for applications requiring high transverse strength and toughness, such as valve parts, fittings, and fasteners, shafts, gears, engine parts, chemical process equipment, paper mill equipment, aircraft components and nuclear reactor components.

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No problem. I have a degree in Mechanical Engineering and a machine shop in my garage so it is more hobby than altruism. I am going to machine another prototype by hand and use the prototypes to test various hardness/toughness combinations. The material is 15-5 stainless which is a precipitation hardening material. That means you heat to a time and temp for a specific hardness. No quenching, no tempering. It is much easier to hit targets with than with more conventional alloys. The strength and toughness characteristics of this material are very good. It is used extensively in the aerospace industry for mission critical parts. I am sure it is very much up to the fairly simple task of transmitting energy from the barrel to the bolt face.

 

I think I will apply different heat treatments to the two pistons, one softer one harder, and see if one bends or breaks.

 

Really, you should see some of the materials I have seen used for semi-auto rifle pistons. I have an original Rhino M-16 piston conversion and the piston is quite simply 1/8" drill rod. It actually worked quite well, although it has long since been retired to the old gun parts pile.

 

Clearly, the only reason for these pistons would be 922r compliance and, for that reason, it is a dumb project. Still, I try to do what I can to abide by all of the laws that govern our society, even the stupid ones.

 

I will post pictures when I get the other made and then, to the range. Now that will be the best part, trying to break them.

 

Panabax

 

It would be expensive, but put them in a 4-port barrel and run 3" slugs through it. If they don't snap in a couple hundred rounds, it would be a pretty impressive demonstration. Of course, the bolt-carrier would be screwed most likely.

Edited by Unobtanium

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Properties of 15-5 PH Stainless Steel

 

15Cr-5Ni is a martensitic precipitation hardening stainless steel offering high strength and hardness along with excellent corrosion resistance. Generally similar to Custom 630 (17Cr-4Ni) in composition and properties, 15Cr-5Ni is chemically balanced to eliminate all but trace amounts of delta ferrite, thus providing superior transverse toughness and ductility plus a higher degree of forgeability.

15Cr-5Ni has fabrication characteristics similar to those of other precipitation hardening stainlesses, and can be age-hardened by a single-step, low temperature treatment.

It has been used for applications requiring high transverse strength and toughness, such as valve parts, fittings, and fasteners, shafts, gears, engine parts, chemical process equipment, paper mill equipment, aircraft components and nuclear reactor components.

 

Have you thought about using S7? I think that it has considerable merit for this application as compared to 15-5. You will note that the Charpy tests for this material at an HRC in the mid 40's are...impressive. Many times that of 15-5 PH at a comparable hardness.

 

Then again, I'm no machinist.

 

I am impressed that you are taking on the piston! Everyone talks a good game, but this is the first prototype I have seen. Otherwise it's usually "in my buddies friend's work garage we are thinking about maybe..."

Edited by Unobtanium

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Have you thought about using S7? I think that it has considerable merit for this application as compared to 15-5. You will note that the Charpy tests for this material at an HRC in the mid 40's are...impressive. Many times that of 15-5 PH at a comparable hardness."

 

I had not considered it. I understands that the original is stainless and I wanted to duplicate the original as closely as possible. If you go through the stainless alloys generally available, 15-5 and 17-4 look like very good candidates for the original material.

 

S7 is tool steel. S7 is used in machin tool applications for its combination of toughness and hardness. However, I think it is would end up harder than I want it to be. In addition to potential stress and fracture issues, there are also wear issues. Toughness generally goes up as hardness and yield strength go down. Between the gas cylinders on the barrel, the bolt carrier face and the piston, I want the piston to be the softess of the three such that any wear occurs only on the piston. It should have only enough yield strength to handle max loads. Any unneccessary increase in yield strength and hardness will reduce toughness.

 

I plan to heat treat to the low end of the hardness scale and then test for deformation and wear. The 15-5 also has the advantage of very good corrosian resistance in hot caustic environments which I think is a plus for the 15-5 over the S7 given the hot gas working environment.

 

Panabax

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