AR Accuracy Testing At 10,000 Rounds
BY Herschel Smith
5 years, 7 months ago
As a young Marine captain, I was the new officer on a rifle team and remember asking the grizzled old salts who had shot in many an inter-service championship or Camp Perry what the proper cleaning interval was for those incredible Quantico-built National Match M16s. The answers varied from daily on one end to at the end of the season on the other. There didn’t seem to be any real testing to support any given answer, and I accepted that you punched the bore whenever it seemed right.
I recently thought back on that experience as I finished up an endurance test on a Bravo Company Manufacturing (BCM) upper receiver. Over the course of a little more than three years, I had logged the lubrication intervals using FireClean to see how far the AR would run as it got dirtier and dirtier. At the end of the test, I was in possession of a barrel through which I had logged 10,000 rounds and had never cleaned in any manner. In shooting the last thousand rounds or so, I had noticed that the rifle seemed to be still shooting quite well and thought it would be interesting to do a formal accuracy workup. I borrowed a Bushnell Elite 4.5-18×44 LRTS riflescope to give the barrel every chance to succeed, and grabbed some quality ammo.
All firing was done from the prone position with the rifle supported by a Harris bipod in the front and some bags under the toe of the stock. The rifle had a Geissele Super V trigger, which is an excellent duty and snap-shooting unit, but not normally associated with group shooting. The BCM wore a free-floated KeyMod aluminum KMR-A rail and the barrel was a basic government profile 16” with a mid-length gas system and a 1:7” twist.
I fired a couple of sighters to get the LRTS on paper and then the very first five-round group of Hornady Steel Match clustered five .224-cal. holes into a tight .84” group that could be covered by a nickel. That was pretty close to prophetic, as the average of all five groups with the Steel Match ran .89 from the filthy barrel, with the series tallying .84, .85, .86, .72, and one lonely group over one minute of angle at 1.17.
That performance wasn’t an outlier. After 10,000 rounds, the BCM barrel grouped Federal Varmint hollow points into just barely over 3/4 m.o.a. on the low end and averaged just over an inch due to one “large” 1.5” group that pulled the average over one MOA.
Black Hills 69-gr. Sierra Match Kings clustered together consistently, poking holes in a tight knot while maintaining polite separation for each hole at just under a minute on average with .79, .82, .90, .92, and 1.25” groups.
[ … ]
I was somewhere between pleasantly surprised and mildly shocked for the barrel to do this after 10,000 rounds and never had as much as a boresnake, brush, or patch run through it.
I’m not surprised. Eugene Stoner engineered a fine system. Of course, I wouldn’t recommend doing that – this was a stress test of sorts. Increased fouling and friction will only increase wear and metal fatigue. But it’s nice to know that the delivered wisdom may not be so wise after all.
It’s funny how old myths die hard. My son never had any complaints with the weapon system so I never came into it with predisposed prejudice.
On September 11, 2018 at 11:15 pm, Georgiaboy61 said:
@ Hershel
Re:”I was somewhere between pleasantly surprised and mildly shocked for the barrel to do this after 10,000 rounds and never had as much as a boresnake, brush, or patch run through it.”
The old-school convention wisdom found in the military, i.e., especially with those tough-as-nails senior NCOs, was that you cleaned your piece every time you fired it. The Marine or soldier or whoever didn’t even think about getting some chow or rack time until he’d cleaned and oiled his rifle and made sure it was shipshape in all respects.
Maybe you didn’t detail strip the sucker every time, but you darned sure ran a few patches down the bore and made sure the chamber and bolt-bolt carrier were good-to-go.
That was the SOP in the old military of our fathers and grandfathers. It came about in part because of the presence of corrosive prime salts using in primers manufactured during and prior to the Second World War. If the rifleman didn’t clean his barrel down to the metal fairly frequently, and remove those corrosive substances, the steel of the barrel would pit permanently. And the Marine or GI would get “gigged” (reprimanded) by his NCO or officer during inspection…
After the Second World War-Korea era, advances in primer chemistry made possibly formulations which weren’t corrosive, thereby removing at least one rationale for frequent cleanings. Corrosive ammo was in stock for a long time after the war, not only here in the U.S., but in the armories and warehouses of our Allies, many of whom had purchased surplus Garands and 30-06 M2 Ball ammunition for them.
Still, old ways die hard and there remain – right down to the present – Marines and GIs and others – who believe that it is necessary to clean a rifle each-and-every time it is fired.
A second reason for cleaning a firearm each time it is used – is legal in nature. If the owner of a firearm ever has to prove a firearm hasn’t been used, say in the commission of a crime, he can do so by presenting it cleaned and in unfired condition, which can be verified by inspection from a competent firearms examiner or gunsmith.
However, the military and LE communities weren’t the only ones accumulating experience and knowledge upon the subject. In the precision-shooting community, a lot of dedicated long-range varmint hunters, F-class bench rest shooters and service rifle competitors were experimenting with how to best attain – and keep – accuracy and precision in courses of fire. These individuals discovered that it was possible to get excellent, even superb, accuracy over long strings of fire, using a barrel which would be considered by some as “fouled” – i.e., coated with gilding metal deposits on the rifling (lands and grooves).
The thinking of this school was that one cleaned the barrel and firearm of soot and other combustion residue, each time the rifle was fired – but that one didn’t clean to the bare metal by removing copper – until accuracy had degraded sufficiently to make it necessary.
The general process runs as follows: When a rifle barrel has been cleaned down to the metal and is as pristine and spotless as it can get, that’s your baseline.
Using a chronograph to track your muzzle velocities and target data on group size, you can then begin to fire fouling/sighting shots, i.e., both to foul the barrel by laying down some metal in it, and also to confirm your zero. This process is done using a proven, highly-accurate and consistent load for the particular rifle in question.
Each rifle and barrel are different, but once accuracy and muzzle velocity have stabilized and one is attaining a high degree of reproducibility from one group to the next, you have entered the optimal zone of gilding metal deposition in which your best accuracy and precision potential for that rifle/ammunition load have been reached.
As you continue to monitor MV and/or accuracy, you will at some number of shots – typically at least 150-200 but sometimes many more – experience a dramatic deterioration in performance. At which time, it is finally time to remove copper fouling as well as combustion products.
Anyway, those are the two major schools of though to which I have been exposed, through the years. I’ve had very good shooters come down on both sides of that particular debate, and won’t pretend to know which method is best. Other than to say, experiment and see what gives you the best results.
Personally speaking, I have never attained anything like the performance of the BCM mentioned, especially from a semi-automatic firearm – but there’s no reason it shouldn’t happen.
Every once in a while, a “gun guy” runs across a particular rifle which is just as accurate as can be. If you lucky-enough to have one of them – or one of your friends is – count your lucky stars and hang on to it – don’t sell it.
The closest I’ve come to that sort of experience has been with one of my Winchester Model 70 bolt-actions, a Super-Grade, which shoots sub-moa even with factory ammunition from one or two manufacturers. Yeah, I’m hanging onto it… no, I’m not selling it…
Herschel, for what it is worth, AR15 devotees in high-power service rifle competition have been singing the praises of Stoner’s AR15 design for years now, as an inherently accurate design – and have backed up their talk by winning a lot of hardware at Camp Perry and other places. I haven’t read it, but perhaps you’d be interested in Glen Zydiker’s “The Mouse that Roared,” which is a competitors history of how the AR15 took on and beat the big .30’s in service rifle competition….
On September 12, 2018 at 7:31 am, wynn said:
But the man did lube the gun. ARs don’t run long dry.
On September 12, 2018 at 8:28 am, Frank Clarke said:
I came here to ask a question because I’m really not all that well-versed in such things:
“Will leaving an uncleaned barrel to sit for months do a different kind of damage?” It appears from @GeorgiaBoy61’s response that the answer is ‘no’ for modern arms and modern ammunition.
Did I get that right?
On September 12, 2018 at 8:56 am, Fred said:
Better test. Thank you, Sir.
On September 12, 2018 at 11:49 am, Georgiaboy61 said:
@ Frank
“Did I get that right?”
Yes, more or less. I would only add that if you are professional who depends on your particular bang-stick going “boom” every time you use it, you may elect to keep it in old-school, super-clean condition. If you are a soldier or cop, you’ll also have to follow organizational doctrine and SOPs for that as well. If you are regular dude, on the other hand, it’s up to you to experiment and determine what works best for your needs. How your particular rifle functions best, works most-reliably and performs in the field.
On September 12, 2018 at 2:00 pm, Georgiaboy61 said:
Apologies for the stuck “a” key… time to get a new keyboard….
On September 12, 2018 at 7:02 pm, Pat Hines said:
Seems to me that there was a test of an AR in caliber 5.45×39 that demonstrated much the same thing. ARs are tough and reliable. Lubing the bolt rings isn’t the same as cleaning the rifle.
Thanks for the initial post, Herschel.
On September 14, 2018 at 4:17 am, Nosmo said:
It’s long been a shibboleth among gunnies that “more .22s are worn out from cleaning than by shooting,” which may be more than simple work avoidance and might has some basis in fact. Extrapolation to other calibers then become simple word substitution. (It should be noted that, bore cleanliness aside, wax-lubricated .22 ammunition does create a need for more frequent attention to the action, especially if it’s semi-automatic in operation.)
The anal-and-OCD-set among us (benchresters) clean, disinfect and sterilize with religious conviction (dual addiction to Ed’s Red and J-B Bore Cleaning Compund is a common ailment, often accompanied by stock ownership in a cleaning patch manufacturer); having had membership in that cult some years back I understand the fervor. John Wesley ain’t got nothin’ on benchresters.
I’ll support GB’s thesis: if it’s a critical life support tool, by all means clean it, for no other reason than it’s an excellent opportunity to perform inspection and necessary maintenance; replacing even mildly suspicious components is a great deal more preferable than discovering their inadequacies in actual use. And, for the AR-families of tools (and, by extension, anything gas operated) it’s useful to stay ahead of maintenance needs, if for no other reason than each gun has a window length of X number of rounds between potential important cleaning/adjustment requirements; the inspect/clean/maintain process resets that X number to zero, which is useful. Modern chrome bores, coupled with modern non-corrosive ammunition, permit devotion of greater attention to what’s often regarded as merely the supporting cast – the moveable parts – rather than unrelenting focus on the barrel.
On September 15, 2018 at 7:23 am, James said:
I thank you for doing this,as I do not have the will power to “not clean” my firearms for such a long period and am happy to see that the rifle came through basically unscathed.I change my motor oil on a regular basis in me trucks ect. andas Nosmo pointed out feel the same in that it allows me to inspect the car overall and it’s health/needs ect. like a firearm,that said,tis nice to know there is room for lack of cleaning if the circumstances dictate you cannot clean.
On September 19, 2018 at 9:49 pm, Jaque said:
I don’t see any mention of the barrel make and twist and lining chrome/ stellite/ and rifling type on the test rifle. Also environmental conditions in storing the weapon. All play a part in bore life.
These all have an influence in barrel life. Was the barrel air gauged before and after ?
A great test all in all. Did you have uncle working in an ammo plant ?