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So I shot my MR556 with my Gemtech G5 suppressor attached for the first time and I was shocked just how quickly the barrel got red hot. After shooting a little over 100 rounds the barrel and suppressor got so hot that it melted my high temperature gloves I use to handle hot suppressors. Makes since that without the heat being able to transfer to the bolt and carrier it all gets transferred to the barrel and suppressor. Does this get ever worse with the shorter barrel lengths?
 

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The amount of heat that the BCG would absorbe makes zero difference in the temp of the barrel. The BCG is not a heatsink.

What matters is the fact that you have the supressor attached which allows quicker heat buildup and more heat retention, and of course the rate of fire.

My guns have always heated up faster when shooting suppressed, and of course the faster I shoot the faster it heats up and the hotter it gets.

100 rounds is a little over 3 magazines worth. A single magazine shot fast enough will get the suppressor hot enough that it cannot be touched with the naked hand. Three plus magazines worth of ammunition and the gun will be quite hot. But no 100 rounds will get any gun, suppressor or no, red hot, no matter how quickly you shoot the 100 rounds.

Trust me, i've gotten my M4-96D hot enough that it turned red and I could see where the baffles were because they were a slightly darker red then the rest of the can. Of course it took about 250 rounds to get there.

p.s. the can still runs fine.
 

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Discussion Starter #4
What matters is the fact that you have the supressor attached which allows quicker heat buildup and more heat retention, and of course the rate of fire.
I own more than a dozen suppressors from various companies, I understand about heat retention with suppressor use. What surprised me was that the MR556 seamed to heat up so much faster then a Colt M4 and the only thing that I can contribute it to is the piston operation of the MR556.
 

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I disagree that the BCG and the receiver are not heat sinks on DI guns. The reason I disagree is because the BCG and receiver get frigging hot on DI guns running suppressed. It's simple physics. 100 rounds is a known amount of heat energy. If you apply that heat energy to one mass of material that is less then another mass of material, the lesser mass will obtain a higher temperature faster then the larger mass. There isn't anything you can do about this.

With a DI gun, hot gas is being shot back inside the receiver and onto the bolt carrier. With a piston gun, the gas is mostly shot out front of the gas port, which happens to be right behind the suppressor. I honestly think this could be fixed with an "exhaust pipe" of some sort to vent the gas in another direction, but fixing entails some sort of problem.

The other thing to understand is that the ammo will only create so much heat. While the gun may get hot, and even discolored, it should not be functionally effected. Once the gun reaches a peak temperature, it should stay there no matter how much ammo you shoot. The only factor here becomes the degradation of lubricant, which is much less a factor on a piston gun then a DI gun, since the piston is the only moving part that is getting hot and the BCG remains at a lower temperature that maintains the integrity of the applied lubricant.

-W
 

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I disagree that the BCG and the receiver are not heat sinks on DI guns. The reason I disagree is because the BCG and receiver get frigging hot on DI guns running suppressed. It's simple physics. 100 rounds is a known amount of heat energy. If you apply that heat energy to one mass of material that is less then another mass of material, the lesser mass will obtain a higher temperature faster then the larger mass. There isn't anything you can do about this.
A heat sink is an object that pulls heat away from another object with the intent todissipate the heat quicker and keep the second object cooler.

The BCG does not do this. Just because a small amount of the burning propellant is siphoned from the barrel and used to cycle the gun does not mean that the BCG is pulling heat away from the barrel and keeping the barrel cooler.

The amount of heat from the siphoned gasses is insignificant compared to the heat generated in the barel by burning propelant and friction caused by the bullet traveling down the barrel, with most of the friction heat being generated in the throat as the bullet is initially forced into the shape of the rifling.

With a DI gun, hot gas is being shot back inside the receiver and onto the bolt carrier. With a piston gun, the gas is mostly shot out front of the gas port, which happens to be right behind the suppressor. I honestly think this could be fixed with an "exhaust pipe" of some sort to vent the gas in another direction, but fixing entails some sort of problem.
Like I said, the amount being drawn from the barrel and sent back to the BCG in a DI gun is insignifcant compared to the other forces at work, and certianly not enough to make a noticable difference when shooting suppressed. One thing you WILL notice though is that when running suppressed, the piston guns BCG which normally runs fairly cool, WILL be a fair amount hotter then normal and you will also notice a whole hell of a lot of fouling in the receiver of the gun then normal. Along with this fouling is the heat that was generated when it was created.

This is caused by residual pressure being maintained in the suppressor and then released equally into the barrel as the action opens up, thusly allowing a whole lot of burnt propellant fouling to be released both out of the end of the bore and back into the receiver as well.

The other thing to understand is that the ammo will only create so much heat. While the gun may get hot, and even discolored, it should not be functionally effected. Once the gun reaches a peak temperature, it should stay there no matter how much ammo you shoot. The only factor here becomes the degradation of lubricant, which is much less a factor on a piston gun then a DI gun, since the piston is the only moving part that is getting hot and the BCG remains at a lower temperature that maintains the integrity of the applied lubricant.
-W
Peak temperature? The "peak temperature" of a firearm is dictated by the rate of fire/powder types/ casing shape/etc. vs. the amount of time to cool coupled with all the mechanical factors (material type, thickness, profile, surface area, etc). You cannot expect to shoot a gun full auto for magazine after magazine after magazine and expect the gun to reach some mythical "peak temperature" and stay there regardless of how much more and how fast you keep shooting. The firearm WILL continue to gain heat towards the "peak temperature" of the burning propellant which is hot enough to melt steel, but is applied so quickly in a firearm that it is an extended time damage issue based on repetition rather then a single high heat event.

Of course there will be other factors that limit heat buildup past a certian point in this mythical excercise such as the fact that after a certian point the rifling will literally be shot out, the barrel will turn nearly white hot and droop and eventually cause the weapon to fail in all aspects. That is the only point at which you will reach your "peak temperature".....when you destroy the gun.

All of that being said, it is not the minute amount of gas siphoned from the barrel in a DI gun that makes it "seem" cooler when shot with a suppressor, it is not the piston assembly of a piston gun that makes it "seem" hotter. A gun with a suppressor heats up quicker then a non suppressed gun simply because the heat is retained and vented back into the firearm by the supressor itself. All the "seems" in this entire thread are most likely caused by the fact that the op probably really didn't pay attention to the heat buildup until now. My bet is that it's all about perspective at this point.

Wanna prove me wrong? Get the proper temperature measuring equipment and develop a set firing schedule and measure heat buildup from one gun to the next. I'm pretty sure that the differences will be insignificant, but i'm willing to be proven wrong.
 

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The video posted by H7K is an M4A1 with a heavy barrel:

M-4A1 Firing Test - Video Library - The New York Times

Data from the test:
Barrel Smolders and Glows: 1:48
Guard Assembly Catches Fire: 2:22
Fails to Fire Automatic: 4:47
Shots Fired: 911

Here is a video of a standard M4, with a lighter/thinner barrel then the M4A1:

M-4 Firing Test - Video Library - The New York Times

Data from test:
Barrel Droops: 1:20
Barrel Ruptures: 1:51
Shots Fired: 535

A significant difference.

These tests were performed by Colt, after the Battle of Wanat, on a request by the US Army. During the battle, 9 US servicemembers were killed, many more wounded. In the aftermath, there was a lot of speculation and fingerpointing in regards to the reliability of the M4 platform, as many soldiers reported that their weapons malfunctioned. Some SAW's started to malfunction after a while as well. It turned out that the issue was not the reliability of the system, the guns worked fine....UNTIL the rate of fire exceeded tolerances, and the barrels overheated causing the failures you see in the videos above. Of course, the rate of fire in the videos is unrealistic in a combat situation, but if you factor in the temperature in that area in June, you get an extra heating factor.

An article covering this:
What Really Happened at Wanat | U.S. Naval Institute

Here is a test done to show temperature differences in a DI and piston system:

Piston v. DI temp measurements - M4Carbine.net Forums

There is not a significant difference. As you can see, the bolt and bolt carrier in both systems stay pretty cool. What really heats up is the flash hider, barrel and gas block.
 

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I'd be very suprised if HK didn't test their weapons to the point of catastrophic failure like this.
This was done with the G36. 900 rds fired in under 4 mins from 9 100-rd Beta drums full auto. The gun fired all 900 rounds and the forearm lit on fire @ 750 rounds.

G3Kurz
 

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The video posted by H7K is an M4A1 with a heavy barrel:

M-4A1 Firing Test - Video Library - The New York Times

Data from the test:
Barrel Smolders and Glows: 1:48
Guard Assembly Catches Fire: 2:22
Fails to Fire Automatic: 4:47
Shots Fired: 911

Here is a video of a standard M4, with a lighter/thinner barrel then the M4A1:

M-4 Firing Test - Video Library - The New York Times

Data from test:
Barrel Droops: 1:20
Barrel Ruptures: 1:51
Shots Fired: 535

A significant difference.

These tests were performed by Colt, after the Battle of Wanat, on a request by the US Army. During the battle, 9 US servicemembers were killed, many more wounded. In the aftermath, there was a lot of speculation and fingerpointing in regards to the reliability of the M4 platform, as many soldiers reported that their weapons malfunctioned. Some SAW's started to malfunction after a while as well. It turned out that the issue was not the reliability of the system, the guns worked fine....UNTIL the rate of fire exceeded tolerances, and the barrels overheated causing the failures you see in the videos above. Of course, the rate of fire in the videos is unrealistic in a combat situation, but if you factor in the temperature in that area in June, you get an extra heating factor.

An article covering this:
What Really Happened at Wanat | U.S. Naval Institute

Here is a test done to show temperature differences in a DI and piston system:

Piston v. DI temp measurements - M4Carbine.net Forums

There is not a significant difference. As you can see, the bolt and bolt carrier in both systems stay pretty cool. What really heats up is the flash hider, barrel and gas block.
I don't have technical experience regarding cook offs. From what I heard, some modern op rod guns (ie. HK416, G36) have higher cook off rates than the M4 and M4A1. G3 kurz's NDIA presentation listed the G36 and HK416's cook off rates as 240-270 rounds. The M27 IAR met the sustained rate of fire without an open bolt. I had emailed HKO about the cook off rate and HKO told me through email that less heat transfer to the bolt was the reason the HK416 and G36 had slightly higher cook off rates than the M4 and M4A1.

If my reasoning is wrong, please let me know.
 

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Our technical manual states that after rapidly firing 180 rounds with our HK416's we need to let them cool off to reduce the chance of a cook off.

If the reason is less heat transfer to the bolt due to the op rod design, I do not know. I find it highly doubtful as I do not think the bolt reduces heat build up in the chamber very much.
 

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Our technical manual states that after rapidly firing 180 rounds with our HK416's we need to let them cool off to reduce the chance of a cook off.

If the reason is less heat transfer to the bolt due to the op rod design, I do not know. I find it highly doubtful as I do not think the bolt reduces heat build up in the chamber very much.
Thanks for the info. Good to know about the cook off listed in your manual. Hopefully G3 kurz can explain the difference in cook off in your manual and his NDIA presentation since he was PM for the HK416. G3 kurz's NDIA presentation and HKO said the cook of rate for the G36 was around 240-270. The explanation put forward by HKO technicians when I emailed them was that the bolt head is cooler with the pusher rod gun. The tech guys at HKO said with DI "especially the bolt head is affected when getting hot by the gas and heat which travels the gas tube which ignites the primer very quickly as the primer is most sensitive regarding heat."
 

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Well, a cook off is not a result of a hot bolt face/head, but a hot chamber igniting the propellant inside the case. If a hot bolt face/head was the issue, an open bolt design would be kind of pointless. The open bolt design is to remove the cartrigde from the source of heating, the chamber.

A cook off basically mean a thermally induced discharge, as opposed from the firing pin striking the primer, causing the propellant to ignite. It can be slow; a cartrigde in a hot chamber, or fast: a cartrigde thrown into a fire.

As far as the cook off number, remember that the figure provided by G3Kurz is when cook offs start to happen. The figure provided in our manual is when we need to start cooling off our guns, to avoid cook offs being an issue after firing an additional 2-3 mags. There is no disconnect between the two figures.
 

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I'd be very suprised if HK didn't test their weapons to the point of catastrophic failure like this.
I'd be suprised of this as well.

That being said, with all of the hype and infomation release on various tests that the 416 series has been subjected to, if this test has in fact been performed, why havn't we heard or seen anything of it?

Bueller?

Bueller?
 

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Well, a cook off is not a result of a hot bolt face/head, but a hot chamber igniting the propellant inside the case. If a hot bolt face/head was the issue, an open bolt design would be kind of pointless. The open bolt design is to remove the cartrigde from the source of heating, the chamber.

A cook off basically mean a thermally induced discharge, as opposed from the firing pin striking the primer, causing the propellant to ignite. It can be slow; a cartrigde in a hot chamber, or fast: a cartrigde thrown into a fire.

As far as the cook off number, remember that the figure provided by G3Kurz is when cook offs start to happen. The figure provided in our manual is when we need to start cooling off our guns, to avoid cook offs being an issue after firing an additional 2-3 mags. There is no disconnect between the two figures.
Thanks for the info and for clarifying the differences for me, makes sense. I know the chamber heat is the major reason but what I stated was the explanation given to me by the technicians at HKO on why the G36 had a slightly higher cook off rate than the M4. IIRC G3 kurz said 180-210 was when cook offs start to happen with the M4 and 240-270 was when cook offs start to happen with the HK416 and G36 (if I'm wrong or misquoted you, please correct me G3 kurz).
 

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Well, to speculate on the numbers, and going with the M4 as the comparison weapon, I would suspect that the difference is mostly in barrel design and "weight". The M4 barrel heats up faster, and fails faster than an M4A1 barrel.

It would be easier if you had a link to the document you speak of.....
 

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Well, to speculate on the numbers, and going with the M4 as the comparison weapon, I would suspect that the difference is mostly in barrel design and "weight". The M4 barrel heats up faster, and fails faster than an M4A1 barrel.

It would be easier if you had a link to the document you speak of.....
Sure I'll give you the link to G3 kurz's NDIA presentation. http://www.dtic.mil/ndia/2008Intl/Schatz.pdf

Cook off data on page 157.

I know the M4A1 has a thicker barrel than the M4 and thus the higher cook off rate. But the G36 has a thin barrel and it seems the cook of rate is higher than the M4.
 
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