View Full Version : how much shooting is too much for LWT barrel?
Hey There!
I have 6920 but am looking for a second ar. I know that the 6720 uses a LWT barrel and that it will heat up faster, not as durable as a 6920 because of the heavier barrel. Other than that they are virtually the same except for sights. But my question is how much shooting in a session will the LWT barrel begin to show its weakness? In other words, if I shot both of them side by side for 200 rounds will there be a difference? 300 rounds? 500 rounds? I know this may seem silly but if the argument for having a 6920 over the 6720 is because of the barrel then what real world difference is there when shooting them?
Thanks.
I too am curiouse about this
I just bought a 6720 and haven't had any problems yet but would also like to know if there are any limitations with the barrel.
Heavy Metal
03-06-12, 20:19
The 6720 and the 6920 are both the same weight from the front sight base to the chamber. This is where the barrel dies anyways. I personally don't think the extra mass from the FSB forward makes much difference in anything short of a deliberate attempt to cook the hell out of the rifle.
On a semi especially, all it is is dead weight.
In a discussion I was in elsewhere a guy said the government profile barrel was taken up to prevent the bending of barrels which apparently happened due to soldiers in Vietnam using their guns with the bayonet attached to open crates and such. He is yet to dig up an old write-up for me on it. I'm still learning so I'm not 100% sure of all this.
On that note,
I've seen light weight barrels go through a lot. They heat up faster, but cool faster. I'm not sure there's much bad about them aside from that there's a point groups open up and you need to let 'em cool. That's me mostly speaking from experience with a couple KISS rifles which since the 70's have shot straight and true. I personally think the light weight profile barrels are the most practical unless you're in battle having to provide some full auto support- which does happen.
Markasaurus
03-07-12, 08:05
In a discussion I was in elsewhere a guy said the government profile barrel was taken up to prevent the bending of barrels which apparently happened due to soldiers in Vietnam using their guns with the bayonet attached to open crates and such. He is yet to dig up an old write-up for me on it. I'm still learning so I'm not 100% sure of all this.
On that note,
I've seen light weight barrels go through a lot. They heat up faster, but cool faster. I'm not sure there's much bad about them aside from that there's a point groups open up and you need to let 'em cool. That's me mostly speaking from experience with a couple KISS rifles which since the 70's have shot straight and true. I personally think the light weight profile barrels are the most practical unless you're in battle having to provide some full auto support- which does happen.
I believe that is a myth, I sure hope that most soldiers knew better then to use their rifle as a pry bar! I think the thicker barrel was added due to battle experience. I knew a guy who was in the Vietnam war. One night his company was defending the perimeter against a viet cong attack. He said he fired off so much ammo so fast in his M16A1, the barrel glowed red hot and wilted and bent itself like a piece of licorice.
I believe that is a myth, I sure hope that most soldiers knew better then to use their rifle as a pry bar! I think the thicker barrel was added due to battle experience. I knew a guy who was in the Vietnam war. One night his company was defending the perimeter against a viet cong attack. He said he fired off so much ammo so fast in his M16A1, the barrel glowed red hot and wilted and bent itself like a piece of licorice.
A position I'm sure we all hope to never be in....
My guess is that the majority of us will be ok with the use we get out of the LW barrels. However I am still curious as to the limits they have.
I believe that is a myth, I sure hope that most soldiers knew better then to use their rifle as a pry bar! I think the thicker barrel was added due to battle experience. I knew a guy who was in the Vietnam war. One night his company was defending the perimeter against a viet cong attack. He said he fired off so much ammo so fast in his M16A1, the barrel glowed red hot and wilted and bent itself like a piece of licorice.
The gas tube would probably fail far before the point that the barrel would melt.
And as for knowing what to actually use your rifle for...
Ive seen many times Marines use their rifles to drive in tent stakes and saw two Airforce guys playing gladiator and sword fighting with M16s. I can absolutely see them using it to open ammo crates.
Why are people obssessing with silly stuff like this? Most people cannot afford the ammo to even make it happen.
Shoot the damn thing and enjoy it. Worry about the other stuff later.
Hey There! I have 6920 but am looking for a second ar. I know that the 6720 uses a LWT barrel and that it will heat up faster, not as durable as a 6920 because of the heavier barrel. Other than that they are virtually the same except for sights. But my question is how much shooting in a session will the LWT barrel begin to show its weakness? In other words, if I shot both of them side by side for 200 rounds will there be a difference? 300 rounds? 500 rounds? I know this may seem silly but if the argument for having a 6920 over the 6720 is because of the barrel then what real world difference is there when shooting them? Thanks.
There is a thread, likely a few, on 6920 / 6720 comparisons.
I transitioned from a 6920 to a 6720 as a primary. During multiple classes and range sessions with each, I discern no difference between the two other than the effects of weight during prolonged shooting sessions and carrying it around.
My initial function test of my 6720 was 2000+ rounds in about three hours. It worked, and the lightweight barrel put rounds where I pointed it.
I too am curiouse about this
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Heavy Metal
03-07-12, 14:06
A position I'm sure we all hope to never be in....
My guess is that the majority of us will be ok with the use we get out of the LW barrels. However I am still curious as to the limits they have.
The LW Carbine profile is exactly the same as the M-16A1.
Heavy Metal
03-07-12, 14:08
The gas tube would probably fail far before the point that the barrel would melt.
And as for knowing what to actually use your rifle for...
Ive seen many times Marines use their rifles to drive in tent stakes and saw two Airforce guys playing gladiator and sword fighting with M16s. I can absolutely see them using it to open ammo crates.
But you know better than to use it as a blunt insturment. The LW barrels are the way to go on a Semi. No need to carry any parasitic weight around. Carry something useful in its place like a good blade or more ammo or more hydration.
Grumpy MSG
03-07-12, 15:02
I believe that is a myth, I sure hope that most soldiers knew better then to use their rifle as a pry bar! I think the thicker barrel was added due to battle experience. I knew a guy who was in the Vietnam war. One night his company was defending the perimeter against a viet cong attack. He said he fired off so much ammo so fast in his M16A1, the barrel glowed red hot and wilted and bent itself like a piece of licorice.
Casull, it was actually the original 3 prong flash supressor that people were using to snap the bands on the ammo crates. If you don't believe people were doing it, just try to find some of the early P.S. Magazines (the Army Maintenance comic book) and see if they don't mention it.
Markasaurus, the gas tube will in fact get to glowing under high volume of fire circumstances and probably fail before the barrel ever would. the barrel wouldn't "Bend like a piece of Licorice", if you got it good and hot (glowing gas tube hot, which was from probably about 300 rounds in approximately 2-3 minutes when I saw it happen) and then leaned the hot barrel against a tree, I would believe it would probably change the point of aim versus point of impact, I do know that it would take far less rounds than that to melt a sandbag or rifle sling to a hot barrel and make a nasty mess.
I know the M16A1s had 210 rounds fired through them during live fire exercises in a short period and they seemed to handle it okay.
Thank you that was what I wanted to know!
"My initial function test of my 6720 was 2000+ rounds in about three hours. It worked, and the lightweight barrel put rounds where I pointed it. "
I had a 6520 a few years back and the groups would indeed open up a little after a rapid fire mag or two. But even when they opened up it was still plenty accurate. I never did an official measurment but that rifle would group good ammo at around 2.5-3 inches at 100. After prolonged fire it maybe opened up to 4-5 inches. All done with irons. A 5 MOA group will still hit a man sized target at 400 yards.
Grumpy MSG, I have seen the gas tube get red hot really fast. I think you're pretty on with your statements.
Heavy Metal
03-07-12, 22:05
Let me see, an M16A1 set on rock n roll, 5 magazines 50-50 ball-tracer layed out in series and an order to burn off all opened ammo.
....all at night.....yep, that was fun!
The front three inches of the gas tube was glowing cherry in the dark when I had finished the 5th magazine.
Folks, that old 'pencil barreled' A1 only had a chrome chamber, no chrome bore and it shot like a champ thereafter.
Alaskapopo
03-07-12, 22:15
I had a 6520 a few years back and the groups would indeed open up a little after a rapid fire mag or two. But even when they opened up it was still plenty accurate. I never did an official measurment but that rifle would group good ammo at around 2.5-3 inches at 100. After prolonged fire it maybe opened up to 4-5 inches. All done with irons. A 5 MOA group will still hit a man sized target at 400 yards.
Good enough for what, shooting barns? If I had an AR that would only do 2.5 moa at its best I would get a new barrel. Sure if you only plan on shooting in CQB situations that is fine. But you may have to stretch your rifles legs in real life from time to time.
Pat
GeorgiaBoy
03-07-12, 22:32
Good enough for what, shooting barns? If I had an AR that would only do 2.5 moa at its best I would get a new barrel. Sure if you only plan on shooting in CQB situations that is fine. But you may have to stretch your rifles legs in real life from time to time.
Pat
Isn't the mil-standard of accuracy for the M4 something like no worse than 4 or 5 MOA at 100 yards with M855?
Regardless, I would be ok with a 2.5 MOA barrel. A defensive carbine doesn't need tedious accuracy ability at ranges past 100 yards IMO. It shouldn't be slinging rounds everywhere or anything, but I don't need a sub MOA barrel.
It's something that I know it's a "pix or it didn't happen" but I've seen SUB-MOA out of one "all my life" and always thought it was normal before I was into AR's. It was an SP-1 but I'm sure that must say something. Then of course we can look at the SCAR being pretty much a light weight profile... yet it's very favored.
I don't really see a huge disadvantage with a LW barrel as long as it's of good quality.
Alaskapopo
03-08-12, 00:36
Isn't the mil-standard of accuracy for the M4 something like no worse than 4 or 5 MOA at 100 yards with M855?
Regardless, I would be ok with a 2.5 MOA barrel. A defensive carbine doesn't need tedious accuracy ability at ranges past 100 yards IMO. It shouldn't be slinging rounds everywhere or anything, but I don't need a sub MOA barrel.
I know 2.5 MOA can be fine for a defensive rifle but I want much better. Assuming I am using good ammo I want at least 1.5 moa and when accuracy falls to the point where it can't do 2.5 moa I will get a new barrel. The military standard with M855 is a very low standard.
Pat
http://www.ar15.com/forums/t_3_118/486023_Accuracy_Evaluation_of_a_Colt_16andamp_quot___Light_weight_Barrel.html
Interesting to note
The barrel on the Colt 6721 is the most accurate "off the shelf" chrome-lined, NATO chambered AR-15 barrel that I've tested.
and then he posts a picture of a group 0.87", and the best group he posted with the 6520 was 0.96". Most people couldn't see the difference in the two if the groups were side-by-side.
0.625" barrrels will not automatically group 5" from a cold barrel, will not heat up and bend like liquorice, and will not fling rounds that defy the laws of physics simply because the barrel got warm.
In a chrome-lined barrel the 0.625" profile makes the most sense for most people. If you need a greater degree of precision you should probably be looking at un-lined or stainless steel barrels. If you need a barrel that will withstand volumes of fire it will probably be issued to you.
Well if you want great accuracy while going somewhat light weight look at Centurion's LW barrel. It's sort of a cross between Traditional LW and Medium contour. It's hammer forged, double chrome lined, and apparently* has two times the life of other barrels while being said to have sub MOA if you do your job.
This info is off of their website, and things industry folk have said here and there on this forum as well as others.
Here's a quote from Monty,
It does cut some of the taper bore out but it will still shoot with or better than any of the other barrels on the market that don't have it.
Also I'm planning on pulling the 1 MOA guarantee off the barrels anyway and only applying it to the uppers. There are other factors that go into accuracy and when I ship just a barrel I have no control of the other factors of the build.
Here's a thread on them from here. Will it help? dunno.
https://www.m4carbine.net/showthread.php?t=42471
Well if you want great accuracy while going somewhat light weight look at Centurion's LW barrel. It's sort of a cross between Traditional LW and Medium contour. It's hammer forged, double chrome lined, and apparently* has two times the life of other barrels while being said to have sub MOA if you do your job.
This info is off of their website, and things industry folk have said here and there on this forum as well as others.
Here's a quote from Monty,
Here's a thread on them from here. Will it help? dunno.
https://www.m4carbine.net/showthread.php?t=42471
I have one of these for an article. I'm hoping to do some bench testing with it shortly.
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-ash4/384530_257194714337638_108323505891427_743720_340804820_n.jpg
Looks sweet! I want one. I look forward to whatever you have to say about it.
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