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1/22/2020 12:12:56 PM
Posted: 1/15/2015 8:02:29 AM EST
[Last Edit: 1/15/2015 9:48:31 AM EST by WBlacklidge]


Watched this video and had questions for the more experienced...

Would you have guessed the barrel to fail first? If not what would you have thought would have blown up first?

Would this happen to most all AR barrels or was it likely a defect in the metal of this particular barrel?

In retrospect what would you have done to help prevent this failure?

Would you call this a successful test of the AR/M4?

Below is the link to the GD Thread on the video if you have non-technical comments:
GD Thread


Link Posted: 1/15/2015 9:28:33 AM EST
The barrel was of a thin profile from what I see. If not the barrel something else would have went soon.
I have seen others do a similar test with AR and AK's and just about any rifle ends up failing before the 1000 round full auto range.
Link Posted: 1/15/2015 9:39:54 AM EST
[Last Edit: 1/15/2015 9:40:18 AM EST by WBlacklidge]
Yeah that is what GD had to say. The barrel is not at fault and at that round count of cyclic running something was going to fail and it was really a roll of the dice. Also, most would have guessed the gas tube would have gone first.
Link Posted: 1/15/2015 9:41:01 AM EST
I watched it, I thought the whole video was silly in several ways. That channel is a train wreck for me because I do like some of their videos but lately it seems all they do is try to sell stuff.

When he called himself a scientist
Link Posted: 1/15/2015 9:46:36 AM EST
this thing is getting hot.
Link Posted: 1/15/2015 9:46:54 AM EST
I didn't start this thread in GD because I wanted to keep the discussion on the topic of getting more technical information on the failure.

Below is the link to the GD Thread on the video:
GD Thread
Link Posted: 1/15/2015 9:47:07 AM EST
[Last Edit: 1/15/2015 9:49:47 AM EST by Dano523]
Link Posted: 1/15/2015 10:41:20 AM EST
I don't know about guessing the right answer, but when the Army performed a full-auto-to-failure test with an M4 and an M4A1, the round counts were:

M4 made it to 520 before the barrel failed (melted).

M4A1 made it to 922 rounds before the gas tube failed (melted); the rifle continued to finish what was left in the mag by hand and the test was terminated.

I can't find the link to the test vid but I think my round counts are correct.
Link Posted: 1/15/2015 10:45:12 AM EST
Dano, fantastic information! Okay so that really allowed me to put into context the video and what is happening with that failure. So what likely happened is that the barrel heated up to the point where there was 'droop' and that round stressed the metal most likely at the fulcrum/apex/top-of-bend of the drooped barrel?

So I imagine a firearm operating from a closed bolt is inherently more accurate as opposed to the entire mechanical operation that takes place after a trigger pull? Which makes sense for a firearm that is 3-round burst or semi auto.

Thanks for making me smarter on what I just watched!


Link Posted: 1/15/2015 1:01:02 PM EST
There are very few people I would not take to our range...... this dude just made it to that list.........
Link Posted: 1/15/2015 1:10:10 PM EST
[Last Edit: 1/15/2015 1:11:21 PM EST by jaqufrost]
Originally Posted By WBlacklidge:
http://www.youtube.com/watch?v=BSizVpfqFtw

Watched this video and had questions for the more experienced...

Would you have guessed the barrel to fail first? If not what would you have thought would have blown up first?

Would this happen to most all AR barrels or was it likely a defect in the metal of this particular barrel?

In retrospect what would you have done to help prevent this failure?

Would you call this a successful test of the AR/M4?

Below is the link to the GD Thread on the video if you have non-technical comments:
GD Thread


View Quote
It was a .gov profile barrel. If he had used a heavy profile barrel it would have blown the gas tube first. Even without a blow out the barrel was toast by the end of that test. If you just have to be able to keep shooting full auto you could put a V7 Inconel gas tube on a heavy barrel with a heat sink. At that point you will probably need a heavier gas block as that will be the next point of failure.

Other factors that can contribute include the gas port location and type of ammunition used. Hot loads will produce more heat that must be released. A closer gas port is dealing with higher pressures, which means more heat on the gas block and tube. If you look in the Archives, Spikes blew a gas block on their compressor build during full auto testing.

ETA: I left out cyclic rate, the higher your cyclic rate the faster parts go out.
Link Posted: 1/15/2015 1:17:30 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By KILLERB6:
I don't know about guessing the right answer, but when the Army performed a full-auto-to-failure test with an M4 and an M4A1, the round counts were:

M4 made it to 520 before the barrel failed (melted).

M4A1 made it to 922 rounds before the gas tube failed (melted); the rifle continued to finish what was left in the mag by hand and the test was terminated.

I can't find the link to the test vid but I think my round counts are correct.
View Quote
Keep in mind that running drum mags over 30rd mags will kill it a lot quicker. Dano said middle of the 3rd drum, which isn't even a 3rd of the M4A1 numbers. I don't know what rifle setup he had though.

I've done a FA beta dump once and stopped after 100rds. The first 100 is all it took to have a cherry red gas tube. I ended up replacing the tube because I was having corrosion issues. I have also had some corrosion on the gas block that I think is linked back to the FA beta dump.
Link Posted: 1/16/2015 3:01:48 AM EST
Link Posted: 1/16/2015 3:30:27 AM EST
[Last Edit: 1/16/2015 3:36:14 AM EST by Gamma762]
Any barrel, on any kind of firearm can and will eventually fail when subjected to continuous firing without cooling. That's why water cooled machine guns existed, and why machine guns intended for high volume fire have quick change barrels.

The info on the video stated that the test barrel was 416 stainless. 416 is a very poor choice for a high volume fire application as it looses strength more rapidly as heat increases compared to stronger and more heat resistant steels like the CM and CMV types.

A stainless lightweight profile barrel is a bad idea all around and I'm frankly surprised it lasted as long as it did in that test.

Shooter exhibited poor/dangerous gun handling, such as noting that he was getting cook-offs, then continuing to chamber and handle the firearm with it pointed up in the air above his backstop. Just another shining example of the stupidity that is rampant in the new found youtube gun reviews media market. No one in the industry is doing us any favors by supporting these kind of displays.

IIRC there are Colt test-to-destruction videos of even heavy(er) barrel variants which experience barrel failure before gas tube failure, and that's with CMV steel barrels.
Link Posted: 1/16/2015 5:30:55 AM EST
Dano, thanks.

Never actually knew the reason and benefit of an open bolt machine gun until I read your post.

Still learning new things all the time.

Txl
Link Posted: 1/16/2015 9:31:28 AM EST
[Last Edit: 1/16/2015 9:39:04 AM EST by BamaInArk]
Even the German MG-42, designed as a MG(Open Bolt), carried spare barrels due to overheating issues. Physics!


And here's the Colt testing to failure video. Somebody imbed.

https://www.youtube.com/watch?v=Kzfm4pYhIyY

Archived ARFCOM thread http://www.ar15.com/archive/topic.html?b=3&f=12&t=516531
Link Posted: 1/16/2015 9:39:40 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BamaInArk:
Even the German MG-42, designed as a MG(Open Bolt), carried spare barrels due to overheating issues. Physics!


And here's the Colt testing to failure video. Somebody imbed.

https://www.youtube.com/watch?v=Kzfm4pYhIyY
View Quote
Yep, I think the consensus in the bumpsaw thread was to just use a spare upper if you want to keep dumping rounds.
Link Posted: 1/17/2015 9:25:38 AM EST
[Last Edit: 1/17/2015 9:26:37 AM EST by EdDinIL]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BamaInArk:
Even the German MG-42, designed as a MG(Open Bolt), carried spare barrels due to overheating issues. Physics!


And here's the Colt testing to failure video. Somebody imbed.

https://www.youtube.com/watch?v=Kzfm4pYhIyY

Archived ARFCOM thread http://www.ar15.com/archive/topic.html?b=3&f=12&t=516531
View Quote

Link Posted: 1/17/2015 5:34:14 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By EdDinIL:

http://youtu.be/Kzfm4pYhIyY
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By EdDinIL:
Originally Posted By BamaInArk:
Even the German MG-42, designed as a MG(Open Bolt), carried spare barrels due to overheating issues. Physics!


And here's the Colt testing to failure video. Somebody imbed.

https://www.youtube.com/watch?v=Kzfm4pYhIyY

Archived ARFCOM thread http://www.ar15.com/archive/topic.html?b=3&f=12&t=516531

http://youtu.be/Kzfm4pYhIyY


Gas tube melting is pretty benign. Barrel blowing OTOH, is not so much,
Link Posted: 1/17/2015 6:30:42 PM EST
I remember a recently pictured posted by an Army Ord. guy with four or five M4 profile barrels that burst midway between the chamber and front sight tower.

Extended full-auto will break shit. There is no way that pencil barreled section is going to last glowing red hot and still running mag dumps.
Link Posted: 1/17/2015 11:37:04 PM EST
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