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panabax

USA Made M4 Gas Piston Prototype

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The outside diameter of the factory piston appears to be ground and polished. Are you planning on undertaking that step as well. I too was contemplating the issues in duplicating the part. As you pointed out the radial grooves is the biggest headache. I was concerned about the seal to the cylinder. If the piston is too rough (or the material too hard, or you leave a burr) I would be concerned about damaging the cylinders. Near as I can tell that means buying a whole new barrel assembly.:eek:

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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

 

The lowest hardness I have seen for S7 is HRC 45. At that hardness it has a Charpy C-notch (not V, could not find V for it) of over 200J

 

I am curious how hard the OEM piston and OEM BCG are. Would be worth testing.

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The outside diameter of the factory piston appears to be ground and polished. Are you planning on undertaking that step as well. I too was contemplating the issues in duplicating the part. As you pointed out the radial grooves is the biggest headache. I was concerned about the seal to the cylinder. If the piston is too rough (or the material too hard, or you leave a burr) I would be concerned about damaging the cylinders. Near as I can tell that means buying a whole new barrel assembly.:eek:

 

I am not planning on grinding the diameters on the rings. They will be polished. I agree that the wear part must be the piston not the cylinder.

 

Panabax

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The lowest hardness I have seen for S7 is HRC 45. At that hardness it has a Charpy C-notch (not V, could not find V for it) of over 200J

 

I am curious how hard the OEM piston and OEM BCG are. Would be worth testing.

 

Yes, the S7 is very tough and very hard.

 

Max hardness for 15-5 is attained at a 900 degree temp with a Rockwell C of 44 and a yield strength of 175,000 psi. At 1150 degrees is goes to Rockwell C 28 and a yield strength of 125,000 psi.

 

I agree that a hardness test on the factory piston would provide very useful information. Unfortunately, with all my skill and good looks, I don't have the necessary equipment. Anyone out there have a hardness tester in their garage?

 

Panabax

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Lest some of you think I am all talk and no game, attached below are pictures of the latest prototypes of a US manufactured M4 gas piston. This is a lot of 20 CNC turned pistons. I will need to make the radial cuts in the rings manually and do the heat traeting. Hopefully this will be done in the next two weeks so I can test them out, which I will do thoroughly (that's really the fun part, right?).

 

I was very pleased with how these turned out. I will keep you posted.

 

Panabax

 

 

 

 

 

 

piston_1.jpg

 

 

 

piston_2.jpg

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Wow. Good luck Pana. Hopefully it all ends up well and good for you. Then you can let us know how to get our own. (wink, wink; nudge, nudge)

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Hey look!!...off on the horizon!.....922r compliance with a collapsable stock!

 

:)

oh YEAH, its not the collapsible one!! and when the c-stock does FINALLY come out, im sure it will not be as good as the OEM one!!;)

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Here is a picture of a pair of completed pistons with the gas cuts made in the appropriate locations. Time to heat treat and then the fun part, testing.

 

Panabax

 

m4_piston_2.jpg

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Panabax, you're my hero!!;) now remember if they do work out just fine and pass all testing, dont forget im your first customer!!:D and thanks for taking on this arduous task!!

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Here is a picture of a pair of completed pistons with the gas cuts made in the appropriate locations. Time to heat treat and then the fun part, testing.

 

Panabax

 

m4_piston_2.jpg

 

Forgive me for asking, What advantages do these have over the factory parts.

 

What will they cost.

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Forgive me for asking, What advantages do these have over the factory parts.

 

What will they cost.

 

I imagine a "Made In USA" stamp will be the advantage.

 

And given the work involved.. I bet they will cost a pretty penny.

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I imagine a "Made In USA" stamp will be the advantage.

 

And given the work involved.. I bet they will cost a pretty penny.

everything said above is correct!! i can legally have my collapsible stock and ALL my other goodies legally with these pistons!!!!!;) and to be honest, i dont care what they're gonna cost, just get em!!:D

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So this is for more the 922r laws.

 

Thanks for all your hard work.

YUP!! why else would anyone want to take on this arduous task??:D cause to be honest, the OEM ones work just fine!!;)

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Great work. It doesn't matter how much it costs or how many get sold. Just having the details posted on the Internet is very helpful (to me:cool:)

 

Confidentially, i'm working on my own version.

 

1) Buy 2 suitable "piston blanks", e.g. Brownell's SKU #:301-000-512 (or use the two that came in your M4)

2) Make substantive changes to the piston blanks:

a) Stone off any sharp edges

b) Heat treat by alternating between a refrigerator and kitchen counter to to "relax" the metal.

c) Demagnetize the blank.

d) Polish portions of the shaft.

e) File a flat on the blank.

f) Go to the Mall

g) Stop by "Things Remembered"

h) Have them engraved "Made in USA"

 

Note: Steps a-e are optional. Its simpler to say you purchased the items from "some guy" on the Benelli forum.

 

If you use the "piston blank" turnings that came in your M4, your total cost will be $9/piston for the engraving. If you tell them these are gifts for your Grandma, who happens to be named "Ursula Stanford Abrahms", and just get her initials engraved, it's only $3/piston!

 

YOU GUYS WORRY WAY TOO MUCH! :eek:

Edited by OhioM4

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YOU GUYS WORRY WAY TOO MUCH!

in this day and and age one cannot worry too much!! people are getting arrested for the STUPIDEST THINGS lately,that they never did before!!;) and heck as bad as CRAZIFORNIA is, you can almost get arrested for being white and standing on a street corner...:p

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The whole thing is like a Kafka novel. You can't win, heck you can't even learn the rules. Even the folks with letters from the ATF... ARE NOT SAFE! There is no precedent that the letter will save your butt (or even your gun). The "man" has been inconsistent in answering our inquiries and some of the letters posted were not even signed by a person. They reserve the right to change their mind anytime they feel like it and there is no guarantee you will even get your day in court. If they want you, the part count will suddenly change to 15.

 

As to the "Made in USA" security blanket, there are not any real rules except for textiles, furs, and automobile parts. Our wonderful gubment cannot agree on what "Made in USA" actually means, much less write any coherent laws, regulations, or rules on the subject. I just proved that a part stamped "Made in USA" can be counterfeited for $3! I have to imagine the burden of proof is on you! Can you prove where the steel was originally smelted? What about all the additives and alloys? It's a false security, you're chasing after some vague 922r compliance and stepping into a whole new world of vague FTC "Country of Origin" compliance issues.

 

Why is everyone doing this? My M4 with PG stock will blow just as big a hole in someone as the "Tacticool" version. You are risking a lot for vanity. If you really "need" the "evil" features...and are worried about 922r compliance...buy another gun!

Edited by OhioM4

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