Being one of the proud 1/7 20" AR owners, I've yet to shoot anything but Q3131A  M193.
I look foward to shooting some of the heavy(75, 77) loads, however I've thought about the possible wear it may cause to my fav Colt.
So, please help me understand the risk's if any??

Should I look for a 30% increase in wear?

BBl life?

Chamber pressure/life?

Bolt assy----ect ect

Sorry for the "dumb ques", and thanks for your help guys.

NOT a dumb question.

Reduced life in both bolt and barrel.

(There just ain't no FREE lunch.)

5sub

Lighter bullets will cause more wear on your barrel, due to increased velocity. (under 50gr varmint rounds)

Hmm...heat is a much worse culprit of barrel wear than the actually mechanical wear.

IMHO, 75-75 grain bullets would in theory cause more wear because they have higher polar intertia and thus place a higher strain on the throat.  But I doubt it is a significant amount.

Rifling further down the bore would see less because the bullet is moving slower.  Maybe, maybe not.  Probably doesn't matter.

If you don't get your gun too hot, it will last just as long as any other chrome bore.  Insignificant.  next to unmeasureable is my guess.

With a1/7 I'd never shoot anything under 55grn

My 02' Mt6601 is not chrome lined??

Some questions are completely academic in nature - and the answer really doesn't matter.

This is one of them.

Don't worry about it.

Thanks man, Thats what I thought.  Use the Q most times and the 77 BIG BOYS as a spl treat.[:D]

GtDude,
[b]The Army Marksmanship Unit (to name one) feels this question is NOT academic.[/b]  Due to the added stress from shooting the longer, heavier bullets, this unit changes both bolt and barrel about every 2500 rounds.  And yes, our forward deployed troops in the Middle East are going to run into this new requirement.

Like I said, there ain't no free lunch.

Sometime when we're all bored schitless we oughta get into why the damn 1:7 barrel ever came into play. (Had to do with the SAW, Artic tests and the Geneva Conventions !!  (LOL!)

5sub


(Forest, I know you guys at the Maryland Shooter's site keep track of a lot of good information and I'll send you an IM before tomorrow AM.  I linked to the info you guys have re the Wylde chamber just yesterday.)

Are ya absolutely positive, sub, that it's the heavier weight bullets, that have them changing their bolt and barrels, or could it possibly be that they are loading 'em on the [red][b]RED-LINE[/b][/red] in order to get MAX velocity and this is placing additional stress on both the bolts and "throats" of their barrels. That and the fact they require maximum "accuracy" and perhaps this is why they change so often.

Just wondering....

Mike

Mike,
without atually being there I can't be absolutely positive.  However, I know the person well who was there and he is head of a major firearms manufacturing company (AR type weapons).  That's who my information came from. Yes, I'm sure max accuracy has something to do with the change but he clearly told me the problem also looms for our forward deployed troops.  He and I have had this running email exchange about the 1:7 barrels for a couple of months.  My position is customers want them because the military uses them and his position is that 1:7's are not good for the customers because of the reasons I've stated.  (Week before last, he spent the entire week with the Army Marksmanship Unit.)

Here's his final comment:  "........if there are enough people who insist on dumb barrels, I guess we'd be smart enough to sell them."

Tom

Customers want the 1/7 barrels because they can shoot the 75/77gr bullets that have become popular in the last few years because of their terminal ballistics.  For those customers the 1/7 barrel is not dumb.  You could argue that a 1/8 is a better choice, but the 1/9 on most ARs isn't.  For them.  The other 90% of the shooters who never shoot anything but 55gr FMJ would be better off with a 1/9 (or even 1/12), but they're not the ones asking for the 1/7s.

This is the first I've heard of faster wear for the 75/77gr.  I've heard that 1/7s wear out faster than 1/9s, but nothing about bullet weight until now.  I've always thought that barrels "wear out" from throat erosion caused by  the hot gasses and that the worst calibers for barrel wear were the light, super-fast varmint loads and the big magnums--the ones with lots of powder relative to bullet size.  I would think that the 75/77gr would be no worse than any other bullet, and probably better than the <50gr varmint loads.  

The AMU would change barrels when they see accuracy drop off, but I doubt the typical soldier would ever wear out a chrome-lined barrel enough to notice, regardless of ammo used.

Mike_L.,
I understand why some shooter's want the 1:7 barrels.  I also fully understand why the military had to switch to heavier bullets in the Middle East.  Many people believe 1:7 barrels came about because of the longer tracer rounds and the need for 1:7 to properly stabilize.  Not correct. (Actually, 1:8.75 gives the best accuracy for tracers.)  This whole thing started with my suggesting to this company's president that they should make 1:7 barrels.  I've given much of his response to that suggestion.  This man is the type who actually worries about providing the right equipment to his customers and not responding to the fad of the moment.  However, he'll have to make them (1:7) if enough customers want them.

5sub

MOST of your barrel and throat wear can be indirectly attributed to the amount of POWDER that goes down the bore.  .223 will burn a barrel up, 5.56 faster, 22-250 faster still.  Same with .308 vs .300 WM etc.  Bullet weight is of a lesser concern.  You should be more concerned with shooting 5.56 ammo insteead of .223 and since your shooting M193 already you will see little increase in wear.

2500 per barrel:  This is the service life of a barrel used with high pressures that is not a Krieger.  You replace the bolt with the barrel in a match AR.  I know people who change Rem 700 barrels every 3000 rounds simply to keep sub .25 MOA accuracy.


OH YES PLEASE DO TELL US WHY 1/7 TWIST WAS SELECTED IF NOT FOR THE TRACER....

THE 1:7 TWIST BARRELS CAME INTO BEING WITH THE SAW.
THE BELGIANS (WHO MADE THE SAW) REMEMBERED THE UNACCEPTABLE WOUNDS (ACCUSATIONS OF INHUMANE WEAPON/AMMUNITION) CAUSED BY THE VERY EARLY M-16A1'S WITH 1:14 TWIST BARRELS.  TO PREVENT A POTENTIAL PROBLEM WITH THE SAW, THE BELGIANS DELIBRATELY OVERSTABILIZED THEIR BARREL WITH 1:7 TWIST.  SO, SINCE THE SAW HAD A 1:7 BARREL, THE MILITARY ALSO WENT WITH 1:7 TWIST BARRELS WITH THE M-16.

NOW IF YOU THINK THE ABOVE IS STUPID AND ILLOGICAL, SO DID A FEW PEOPLE WHO WORKED AT ROCK ISLAND ARSENAL AT THE TIME THIS DECISION WAS MADE !

5SUB

I can see this thread turning into a long discussion, but it should be interesting. [:)]

After all that hollering above, I'm too tired to 'dis-cuss' for long.

Original prototype SAW was 1/9 barrel to match the 62 grain ammo FN developed to go with it.  I did a research paper on the SAW a long time ago.  Several texts had conflicting info but noone discussed developing a less lethal 5.56 twist and even if they did TWIST HAS NO MEASURABLE EFFECT ON TERMINAL BALLISTICS.

Second what does Rock Island Arsenal have to do with the twist rate of the SAW?  The Minimi was not developed by them.  They only did testing on SAW applicants.

You are not important enough to me for me to care whether or not you agree with my post.  Agree.....disagree, makes no difference.  Most likely you wrote the specs for the SAW and the M-16 anyway.

Most of your crap isn't worth answering.  As an example I  believe I stated the "Belgians" deveoped the SAW.  As for your statement :"TWIST HAS NO MEASURABLE EFFECT ON TERMINABLE BALLISTICS."

[b]TWIST DOES HAVE A MEASURABLE EFFECT ON THE WOUND CAVITY PRODUCED WHEN THE TWIST WILL NOT PROPERLY STABILIZE THE BULLET.[/b]  IN CERTAIN TESTS (I'M SURE YOU REMEMBER WHICH ONES AND WHERE FROM YOUR TEXT BOOKS), AND UNDER CERTAIN ENVIORNMENTAL CONDITIONS (READ TEMPERATURE), A BARREL WITH A 1:14 TWIST WILL NOT PROPERLY STABILIZE A 55GRN BULLET.  THE RESULT IS A WOUND CAVITY THAT LEAVES THE NATION USING SUCH A FIREARM OPEN TO ACCUSATIONS OF USING INHUMANE WEAPONS AND AMMUNITION.  THE BELGIANS WERE FAMILIAR WITH THE 'PROBLEMS' RESULTING FROM THE 1:14 TESTS DONE ON THE AR-15/M-16 AND DELIBARATELY OVERSTABILIZED THE SAW BY USING A 1:7 TWIST IN ORDER TO AVOID ANY CLAIMS OF UNACCEPTABLE WOUND CAVITIES.

I'M CERTAIN YOU MUST HAVE MISSED THAT FACT WHEN YOU WROTE YOUR PAPER.  

5SUB
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If any other members are reading this drivel, the old story about the M-16 rounds 'tumbling' and therefore causing tremendous wound cavities came about as the result of M-16's with 1:14 twist barrels being unable to properly stabilize the round under certain climatic conditions.  The barrel twist was changed from 1:14 to 1:12 and, as they say, the rest is history.

Today, we well understand that proper velocity causes fragmentation and that fragmentation causes what we now consider an acceptable and deadly wound cavity.  Oddly enough, neither ArmaLite nor the military was aware of this fact until the tests were done.  Bullet fragmentation was an unexpected plus.

5sub

[banghead] Uh Oh...

If it did, would you not use them?  If thats the case, then you dont NEED to use them.

Man, have I learned alot about some of the reasons and theory's behide the 1/7 change.  Thanks all, and keep it going. [beer]

The swap from 1/14 to 1/12 had to do with accuracy concerns and not terminal ballistics.

The 1/14 never caused greater trauma from heyholing in Vietnam.  This occured in artic conditions.  Vietnam did not have those temperatures.

You are correct when you say 1/7 and 1/14 will cause identical wound paths in normal conditions with M193 and the key is [b]velocity[/b] though.

I never disputed the 1/7 starting with the SAW.  I only disputed the WHY it was used.  I have never found any referance to the 1/7 being used to create a rifle that caused less traumatic wounds.  I have read a lot and been on this board for many years and this is the [b]first time[/b] I ever heard the 1/7 was specificaly selected to [b]reduce[/b] the effectiveness of a weapon.  I am sorry but since I cannot find any data to back up your position and you seem to be the only person I have ever heard state that the military thought it needed to reduce the wounding capabilities of its weapons, I have to not believe.  To do otherwise would be foolish on my part.

HOWEVER, if you could provide me with a source for your information I could check out for myself, I would truly appreciate it.

So in conclusion:

Most match shooters change barrels every 2500 rounds.  The fact 1/7 AR shooters do it is only normal, not abnormal.

1/14 was swapped for accuracy concerns in cold weather and has has an identical wound profile to a 1/7 twist barrel in normal conditions.

These are fairly well established facts.  If you have something to show me to dispute these facts please share with us instead of trying to insult me.

Yep, you are correct.  The rifle Al Pacino used in the movie "Heat" was the FNC.

5sub

Sorry Tom, I usually agree with you but I am going to have to go with DevL on this one.

A good friend of my Father, an Army Ordinance Officer, was involved with the SAW trials at Aberdeen back in the early '80s. I have had many long conversations with him regarding the SAW program plus he was kind enough to add a couple of boxes of original FN SS109 and L110 from the trials to my collection.

It is his contention, and every single piece of literature that I have read supports the notion that FN originally developed the XM249 with a 1/9 twist and was happy with its performance but was forced to tighten it to 1/7 to obtain satisfactory accuracy and stabilization with the L110 Tracer in colder temperatures.

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1.  Yes, the switch from 1:14 to 1:12 had to with accuracy.  I never said anything to the contrary.  I did say the Belgians, who designed the SAW, were worried about encountering the same criticism received by the M-16A1 with 1:14 barrels - barrels that would not properly stabilize the bullet under certain climatic conditions and the unstable bullet caused wound channels that were criticized as being unacceptable per the Geneva Conventions.

2.  I'm not going to go back and read my posts but I don't recall mentioning Vietnam.  

Clearly 1:14 barrels would have the most difficulty stabilizing a bullet under artic conditions as opposed to the hot, humid conditions of Vietnam.  

3.  The Belginas did move to the 1:7 with the SAW to avoid any potential criticism of inhumane wounding (see perceptions).  They purposely overstabilized the round by using a 1:7 twist barrel.

4.  Source/s.  I will not give you any definitive information on this subject.

I will represent to you (ALL of you) that my posts are factual to the best of my knowledge.

I will represent to you (ALL of you) that the source/s of this information were either at the actual tests or had access to the original documentation.  I will further represent that this person or perons was/were/are employed at Rock Island Arsenal.  

I will also represent my source/s is/are imminently qualified in our AR world.

Should anyone seriously question my integrity I will give source information to "STRIKER" (Senior Staff).  

Certainly from time-to-time I will post something that is not factually correct.  That's called an error or mistake.  But I NEVER knowlingly lie here on AR15.com.
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We might all do well to remember that in the world of public opinion that perceptions are at least as important as reality (facts). The Belgians feared perceptions and that's the true reason why the 1:7 twist barrels came to the the US military.

5sub

Are you disputing the fact the Minimi was originally 1/9 twist and later changed to 1/7?  1/9 is required to stabilise the 62 grain ammo.  Are you saying the tracer is stabilised in 1/9 or that 1/8.75 would have worked for the tracer and the extra tiny bit of twist from 8.75 to 7 was thought to eliminate serious wounds?

I'm not disputing much of anything.  I made my original post and since that time you seem to dispute every thing.

One last time, believe/do not belive as it matters not to me.

5sub

 From everything I've heard and read;  It's the amount of powder burned and type that wears out the barrel.  As far as wear and tear on the bolt carrier group, I have a bolt group with 8000 rds of the heavy bullets on it.    (every time I build a new rifle I pass on the bolt group)  No problems I just keep changing the gas rings and inspecting the lugs on the bolt for wear.  I am sure I am approaching the limits but figure another 2000rds at least.