Serving as a LEO since 1999.
USPSA# A56876 A Class
Firearms Instructor
Armorer for AR15, 1911, Glocks and Remington 870 shotguns.
The instability Sgt Gold is discussing is a well known fact among target shooters.
You are mixing up the inherent stability imparted by the rifling, which does not change over the life of the barrel with the in flight instability generated by surface turbulence and dynamic imbalance as a result of jacket damage caused by a rough throat.
The older the barrel, the rougher the throat becomes due to flame erosion, and the more damage the bullet jacket suffers. That damage creates inaccuracy in two ways. First, the rougher jacket surface creates turbulent flow around the bullet and second, the damage jacket is no longer as dynamically balanced (you have a rapidly rotating mass, remember) as an intact jacket. Those two conditions create deviations from the perfect flight path in a diverging cone, which means that the area covered by the cone of divergence becomes greater the farther away you go from the muzzle.
That's how a rifle that can only hold say, 2 MOA at 600 yards can probably still shoot slight sub MOA at 200 or 300.
Last edited by Alaskapopo; 01-30-11 at 16:21.
Serving as a LEO since 1999.
USPSA# A56876 A Class
Firearms Instructor
Armorer for AR15, 1911, Glocks and Remington 870 shotguns.
Even when fired from bolt-actioned, machine-rested test barrels at the Lake City Army Ammunition Plant, M855 isn’t capable of producing anything near MOA accuracy; so it certainly isn’t capable of producing MOA accuracy from chrome-lined, government profiled barrels fired on semi-automatic from an M16A2 or M4.
Accuracy Evaluation of Four M855 Loads
I conducted an accuracy (technically, precision) evaluation of four different M855 loads that are currently commercially available, following my usual protocols. This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any Group Reduction Techniques (e.g. fliers, target movement, Butterfly Shots). The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Pictures of the fired shot-groups will be posted for documentation.
All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. The free-float handguards of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.
The test vehicle for this evaluation was a 16” Colt HBAR with chrome lining, a NATO chamber and a 1:9” twist. This is the barrel found on the Colt 6721 carbine. This barrel was free-floated with a 10” LaRue free-float handguard. I specifically choose to evaluate the accuracy this ammunition using an AR-15 with a chrome-lined, NATO chambered barrel, as this is the type of barrel that is most commonly used to fire this type of ammunition.
The 16” Colt HBAR is one of the most accurate “off the shelf” chrome-lined, NATO chambered AR-15 barrels that I’ve evaluated. Three 10-shot groups fired from this barrel from a distance of 100 yards using match-grade hand-loads topped with Sierra 52 grain MatchKings had extreme spreads of:
0.85”
1.14”
0.88”
for a 10-shot group average extreme spread of 0.96”. The mean radius for these three 10-shot groups was 0.32”.
Three 10-shot groups of each M855 load were fired in a row from a distance of 100 yards with the results shown in the table below.
….
All that is necessary for trolls to flourish, is for good men to do nothing.
Where has Noveske ever stated that his barrels would hold peak accuracy for 10,000 rounds? Here is a link to a thread on Sniper's Hide which links to a Q&A with Noveske. The thread is a good read on barrel quality. Excerpt below:
http://www.snipershide.com/forum/ubb...Number=1007086
If you take a manufacturer's statement that he "knows" of some of his button rifled barrels shooting 15k rounds "still in service" as any kind of statement that any given barrel he makes will still shoot its peak accuracy at that round count, then I have several bridges for sale that may be of interest. Note that he indicates that a barrel's end of service life is bullet tumbling, not accuracy degradation.Noveske: All the stainless barrels have…that button that we designed, I call "Improved Polygonal". The polygonal that I used in the past and that some other people are using has one shortcoming, which is an unpredictable end-of-service life. It goes from shooting great to tumbling bullets. Our barrel now gives you a predictable end-of-service life. As it's shooting out, it's going to open up in group before the bullets tumble.
Crane: And how many rounds are you gonna' get out of that?
Noveske: I don't know. I know of barrels that are over 15,000 rounds still in service. So, I don't know how long they'll go, but I know that they're going quite a ways.
I don't want to get caught in a flame war, but threads like this are detrimental to the long term viability of this forum as a place for people to come to get accurate advice. Molon can't be expected to debunk every bogus accuracy thread on the internet, though he does it very tactfully.
Its not just this thread either. I understand that this forum caters to the "tactical" crowd, but too many people shooting carbine classes with off the shelf "tactical" ARs designed for portability and "combat" accuracy make outlandish accuracy claims about their rifle with factory ammo combo. When competition shooters who only shoot hand loaded match ammo from custom built uppers with premium target barrels chime in with experience they get shouted down? Its the old story of people defending the gun they spent $$$ on.
Unless the person is posting pics of groups, or provides some credentials, you should not believe a word that they say about their rifle/barrel/ammo combo's accuracy, or apparently barrel life. Even then you should be skeptical. Sad but true.
Last edited by Zanshin; 01-31-11 at 15:09.
Never did, and I didn't claim a "peak accuracy" to 10,000 rounds. The original poster came up with the first mention of a 10k life.Where has Noveske ever stated that his barrels would hold peak accuracy for 10,000 rounds?
This whole f'n thread is a flame war between tactical class and target/precision class shooters, and their expectation of their equipment.Its not just this thread either. I understand that this forum caters to the "tactical" crowd, but too many people shooting carbine classes with off the shelf "tactical" ARs designed for portability and "combat" accuracy make outlandish accuracy claims about their rifle with factory ammo combo. When competition shooters who only shoot hand loaded match ammo from custom built uppers with premium target barrels chime in with experience they get shouted down? Its the old story of people defending the gun they spent $$$ on.
For MY uses, I fully expect a 10,000 life from my Noveske barrel. I would tell someone on a tactical (ish) forum the same.
This isn't a high power or a benchrest forum. Those shooters will have a MUCH different expectation from their equipment. If this question was asked on sniper hide or brian enos, of course its going to be a different number.
The target audience here isn't high power, benchrest or the like.
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