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Ive seen some threads on here hit on the topic but never any oppions on which one members prefer.

Polymer or Metal...what would you chose and why ?

Would you replace the metal 416 ejection port cover with the mr556 polymer one ?
 

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Theoretically speaking, the metal cover can take more abuse. Although the dust cover isn't supposed to be a high wear or impact item.

On a DI gun, metal all the way due to heat issues and vent gasses coming into direct contact with the dust cover if it's closed and the weapon is fired.

On the 416, this isn't an issue and if the plastic cover holds up durability wise, what's the issue?

There are a lot of end users out there that beat the 416 like a red headed step child and I have yet to hear of a dust cover breaking. But then again, I don't know if the 416D ships with a steel cover or a plastic cover. A quick glance over the 416's imported into America show lots of steel dust covers. Did they ship this way or were they replaced by the end users?

Like I said, so far no complaints to be found.

AGR notes that the 416Ns come with polymer. How have they held up in the cold and in the sandbox so far?
 

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I don't see anything wrong with a polymer cover. For the simple job it does, cover the port and pop open when the bolt is cycled, I can't see that polymer wouldn't do as good a job as metal, especially on a piston gun.
 

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Ive seen some threads on here hit on the topic but never any oppions on which one members prefer.

Polymer or Metal...what would you chose and why ?

Would you replace the metal 416 ejection port cover with the mr556 polymer one ?
Initially the HK416's were fitted with US made metal EPC's. After some time newer HK416's were fitted with a plastic ones made by HK or their sub for that. Primarily because it reduces supply issues and once the mold is made plastic ones are next to no cost to make. Over time HK has made many/most of the parts for these guns as there were supply issues and QA issues with other suppliers. You can best control such things by making all in house or with nearby subs.

As far as performance both are the same and in fact the thicker plastic one may be stronger and less likely to slice open body parts. In fact the first HKM4's made (the HK416 before the Colt suit over the title "HKM4") had no EPC at all and smoked the reliability tests. Port covers are valuable only when you run around with the bolt locked rearward. Many many reliable weapons have no such thing so its usefulness is highly questionable. HK added it to the HK416 because the user community felt more comfortable having it then not becuase it was what they knew.

G3Kurz
 

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AGR notes that the 416Ns come with polymer. How have they held up in the cold and in the sandbox so far?
No issues with the covers, when it comes to durability.

The only issues we have had, is with the EPC spring assembly. It occurs during winter, when people do not lube it properly and moisture gets trapped, it can/will freeze. When people close the EPC, the spring is stuck to the pin and doesn't move, and loses one revolution of tension, rendering the EPC to lose the spring loaded function. An easy fix if it happens, and very easy to prevent by preforming proper field maintenance.

It is a thing that happens, but I haven't seen to many cases personally, maybe 3 incidents over the past 4 years. Never happened to my gun.
 

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The HK416 has a polymer ejection port cover.....at least ours do.
Only the early models came with metals ones. I don't know the date code cut-off, but yep, the all have polymer now. The oldest with plastic that I have seen so far is AH.

It is said that HK found that the polymer ones made for a better seal since they didn't bend. I suspect a big customer had some metal port covers that bent for whatever reason so HK made the change. I will say that the plastic ones are WAY easier to remove than the metal ones, not that you'd have to regulary service that part.
 

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I prefer the metal ones solely for the fact that when I separate the upper and lower, I close the ejection port cover to help hold the BCG in place (as HK bolt won't hold itself in battery due to the firing pin spring). The plastic ejection port cover on my MR556 would not stay closed if you were to hold it vertically (muzzle up), the weight of the BCG would cause it to open.

Pretty minor stuff, but that's my opinion on the matter.
 

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I feel the polymer is better then the metal. The cheap metal these things are made of is very prone to being dented and misshapen very easily to the point that it no longer seals correctly. Polymer either cracks, or it doesn't, usually it doesn't. It doesn't get warped or dented or misshapen.

The downside is that you can't get "neato I'm cool but I've no clue what this really means" stuff engraved on your dust cover for your safe queen.

-W
 

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In nearly 17 years of wrenching on and using AR type rifles, i've never seen nor heard of a dust cover getting bent or being mis-shapen. They are not made from cheap pot metal. Anything that would cause damage to a steel ejection port cover would cause far more damage to the rest of the receiver and if that's the case, then you'd have quite a bit more to worry about then a dust cover that lets a little debris in the action.

I've also never seen anybody get cut or hurt by the steel covers.

As I said, the ejection port cover is neither a high impact or high wear part and a suitably durable plastic part can replace it without much worry for the most part.

That being said, I switched out to a metal cover just because.
 
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