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Discussion Starter #1 (Edited)
So I got the MR416 out to the gravel pit today and did some more tests.

With about 1300 rounds down the pipe now, I started removing gas rings to day to see how the rifle would function.

I removed one gas ring and test fired. Worked fine. Ejected the spent casing and chambered a new round.

Removed a second gas ring, re-loaded and test fired. Ejected spent casing and chambered a new round.

Removed last gas ring and it wouldn't even eject. Cool to know.

Then I swapped out to a different lower with a milspec carbine spring and H2 buffer only to have it not fire.

Checked the hammer and the damn thing was notched so it wouldn't disengage the firing pin safety. F**k.

I'll have to go back and re-do the entire test again because I forgot to check an important part of function while removing the gas rings. That part being to see if the bolt would lock back on an empty magazine with one or two rings removed. I was using a magazine that started out with only 10 rounds in it, and fired one round, then cleared the gun in between stages of the test. I should have loaded two rounds for each test to see if A) the gun would cycle and load a new round and the second to see if the bolt would lock back. That's what I will do next time.

I'll swap hammers in the other lower as well to see if I can get the system to work with a standard lower/spring/buffer and no gas rings.


Now, this is a limited test in that doesn't speak as to the feasability of this should the gun have a much higher round count. As AGR416 said, he has seen a 416N stop cycling with only a single piston ring removed (lost). My guess is that this was on a higher round count gun though with much more wear on the gas rings.

I think that as the round count goes up on this gun, i'll re-do this test every few thousand rounds just to see if it keeps working or not.
 

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I picked up a trade-in lower not long ago, and upon diassembly, I found that the piston (when the op rod was removed) would fall free of the gas block if the upper was pointed "muzzle up". Considering what I know about the gas ring wear in a DI gun, I figured this was not ideal.

I never fired the weapon with that piston, and I have since replaced that gas rings on it, but you have me curious as to what capacity that rifle would be in with gas rings that were that worn.
 

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Discussion Starter #4
Also, the gun I saw it happen to, used a standard HK lower, with an HK spring and HK buffer.

Don't know if that had a say in the matter.
My test was conducted using the HK spring and buffer in an attempt to mimic what you described as close as I could.

I have you to thank for motivating me to try this out to begin with!
 

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I found that the piston (when the op rod was removed) would fall free of the gas block if the upper was pointed "muzzle up".
That is a standard inspection point for our guns, and when what you describe occurs we replace the entire piston, not just the rings.
 

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My test was conducted using the HK spring and buffer in an attempt to mimic what you described as close as I could.

I have you to thank for motivating me to try this out to begin with!
Ok, cool.

And no problem, bro. My "dream" right now would be to draw a new weapon, keep total tally of the rounds fired and see how long it takes to break the gun. Doubt they'll let me though.
 

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That is a standard inspection point for our guns, and when what you describe occurs we replace the entire piston, not just the rings.
Good that's what I did. I would hate to think I cashed out a piston for nothing.

Any idea on what kind of round count (rough estimate) it takes to exhaust a piston to this point? I have yet to experience this on my newer guns.
 

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Not sure, sorry.

I have 10k plus rounds through my gun, and the same piston....I have seen it happen on one gun, and that had around the same round count on it as me.

Might occur more frequently with the 10.5" guns.
 

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Discussion Starter #9
For what it's worth, with only a single ring, the piston will almost slide out on it's own(with a 1300 round count), and with no piston rings, it drops out easily under its own weight when even at a slight incline angle).

I don't think the piston is a high wear item, all things considered, especially since the majority of the contact is between the rings and the gas block, not the piston itself and the gas block, and I'm pretty sure they replace the entire piston assembly is to simplyfiy the supply side and make sure it's the armorers replacing the gas rings rather then having the line troops trying to replace them and possibly bending them or screwing them up. They've already proven that they don't trust the line guys to properly maintinence the small parts of the 416N (as demonstrated by not allowing the troops to service their own AGRs initially) and i'm pretty sure that's the reason for such a broad replacement of the entire piston with rings.

To be honest PB, i'm sure that with a new set of rings, that piston would be just as good as it was when it was new.
 

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Discussion Starter #10
Not sure, sorry.

I have 10k plus rounds through my gun, and the same piston....I have seen it happen on one gun, and that had around the same round count on it as me.

Might occur more frequently with the 10.5" guns.
Just out of curiosity, about what round count did the issue happen? (assuming that the other guy was shooting on a similar firing schedule as yours and was reaching the same benchmarks at around the same time as you) Was it a recent thing at around the 10k mark, or did it happen at the 8k mark or earlier/later?
 

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Maybe it was at 8k rounds.....it happened two years ago.

Oh, and they change out the entire piston for ease of logistics. Should have been more clear. When the piston slides out of the gas block, that is an indicator that the gas rings are worn out.

The pistons we have changed, with actual damage to the piston, is due to soldiers trying to scrape off carbon build up with sharp or abrasive items, and removing the protective coating.
 

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My unit had a quarterly inspection of the HK416's today, including have the updates done to the guns (mentioned in a separate thread).

When my gun was inspected, the armorer said I needed a new piston, as it was a bit loose in the block.

Probably just worn gas rings, but like I stated, we change the entire piston for ease of logistics.

My first parts change, not counting the handguard I swapped.

Here is a picture showing my piston on the right, and a brand spanking new piston on the left:



I have only removed visible carbon build up, so the discoloration is quite clear.
 

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How much rounds does it generally take to wear out the gas rings? How much rounds have your gun fired before requiring replacement of gas rings AGR416?
 

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I have no idea what it "generally" takes.

My gun has maybe 11k through it at the moment.

They are wear parts, and they need replacing when the piston is too loose in the gas block. It is too difficult to provide an exact science answer to the question.

Many variables will affect the life of the gas rings.
 
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