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M4 Gas Piston Tech Data


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does anyone have any tech data on the Benelli M4 gas pistons? Such as what type of stainless steel they are made of? I don't expect to find blue prints of the pistons -- those are fairly easy to blue print anyway.


I'm meeting with a machinist next week in Communist California to see about having US made pistons produced.


Hey SD,


What part of the Peoples Republic will you be in?

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San Pedro, where I'm originally from. Up for the holidays for a few days. There is a lot of talent there along the docks.


I'm grew up in the L.A. area myself and was commuting down that way a lot a couple years ago. My GF is a veterinarian and had an internship in emergency medicine for a year down there in Torrance.



Hookster :)

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I grew up there as well. But moved to a free State in the early 90's. Best lifestyle change ever!

Torrence can be a rough area. I'm sure Michael Vick would love it. Between dog and rooster (their real name is banned) fights, there is something for everyone.


I agree that the heat treatment will be the hardest thing to perfect. I don't plan to do it, we plan to outsource the heat treating process to another company that can assure some level of quality control. Too hard and the pistons will shatter. Too soft and they will deform from impacting the BCG.


I'm looking at finishes also. I think Robars NP3 would be the best. Easy to wipe clean and self lubricating due to the imbedded Teflon.


I spent some time looking at exactly how the ARGO functions. It isn't as much Elven magic as Benelli would lead everyone to believe. If you disassemble the ARGO system, and look down the threaded side of the barrel where the gas plug attaches, you can see the port that opens up to the barrel. It is easy to see why the 4 port models destroyed the BCG and snapped pistons.


There isn't much gas regulation before the gas meets the pistons. Whatever enters the gas ports through the barrel is going to imping the piston. The gas plug will bleed off excess pressure after the cyclic action has occured. The end of the piston actually makes a poor seal against the gas plugs regulator. Chances are, most sissy loads won't even vent out the gas plug. The majority of the gas and suspended carbon will be channeled rearward around the loose fitting pistons. This is why sissy loads cycle slower than full house high brass loads. What is interesting is the 4 port version was unable to bleed enough off through the gas plugs to prevent damage. My guess is the initial spike of pressure was cycling the action before the ARGO had the chance to bleed the gas off.


The reason that everyone says not to oil the pistons is due to the smoke you'll create. The oil will collect carbon deposits too. There is no benefit to oiling them either. The only contact points are polished smooth along theraised ridges of the piston.

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Do you have any spares? If you get some as spare parts there are ways of determining the alloy and heat treatment. Unfortunately, the tests are destructive; grinding spark tests to determine alloy and cutting sections to check heat treatments. The steel companies used to provide some of these services for free to the machine shops. It might be worth asking around. If there is an Engineering college near you, you may find a helpful professor or student willing to do some testing for you for free.

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Good idea about connecting with a college. If I have to buy another factory one, that is fine also. We'll use the best canidate we can find for the job being performed. Then see what the company has to say regarding wha method of heat treatment should be performed. I have a feeling that there is a variable heat treatment on the factory ones. I have snapped a factory piston in the past. So if we have the potential to over-build the piston, we will.


Then, I'll do some real world testing on a set the fun way.


Brownells wants 90 dollars each for a gas piston. That is with my discount. 115 without.

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