meaning of MOA?

[benEzra]

Molon,

Nobody shoots their rifle in a "vise".

Don

He's probably thinking of a machine rest.

 

[Molon Labe]

Molon,

Nobody shoots their rifle in a "vise".

Don

"Machine rest." Whatever.

The point I was trying to make is that a rifle has an "inherent accuracy" independent of the skill of the shooter. To measure this, simply mount the rifle in a sturdy machine rest and actuate the trigger with a solenoid. The pattern after multiple shots will be a 2D Gaussian distribution.

 

[MachIVshooter]

So a rifle capable of, say, 3/4 MOA at 100m is not necessarily capable of 3/4MOA at 900m? I'm guessing that factors both intrinsic to the rifle (bedding, spin rate, muzzle velocity, load consistency), and extrinsic (wind, humidity) play a role in widening the cone of precision?

Here's my chance to learn. Any takers?

Not being a physicist, I will go out on a limb and say that reason for this is going to be external variables, as Medusa oulined. I would hypothesise that, under perfectly consistent atmospheric conditions, the MOA would not change. Meaning, if air density, barometric pressure, humidity, etc. remained the same from muzzle to 1000 yards, 1" @ 100 should be 10" at 1,000. But since no where on earth do such ideal conditions exist, we must go with the phrase Swampy used.

 

[Zak Smith]

Don't forget ammunition variances, which often manifest as elevation error.

 

[USSR]

Nobody mounts their rifle in a machine rest. A rifle that is tested by a gunsmith for it's accuracy is fired by a real live shooter firing off a bench rest. Someone who is a good marksman will have no trouble determining the accuracy, or lack thereof, of a rifle.

Don

 

[Zak Smith]

Nobody mounts their rifle in a machine rest.

Thesis: No person has ever mounted a rifle in a machine rest.

False.

Only one instance is needed to disprove the thesis, but I'm feeling spry-

http://www.researchpress.co.uk/targets/sandyhook.htm

Old Ordnance records show that when fired from a machine rest the .45 Springfield was expected to group all of its bullets inside a 4-inch circle at 100 yards, in a 11-inch bull's-eye at 300 yards, and inside a 27-inch circle at 500 yards.

(the ".45 Springfield" refers to a .45 caliber Springfield trap-door rifle, not the contemporary pistol)

http://www.gunsandammomag.com/reloads/match_0620/

Bo Clerke furnished the pressure barrel for these tests. That took care of the "good barrel" requirement. All the firing was done from a machine rest.

http://www.fulton-armory.com/M1NewRifle.htm

Each rifle manufactured is tested at the manufacturing establishment for functioning and for accuracy, the accuracy tests being made at a range of one hundred yards, using a machine rest

http://hornady.primediaoutdoors.com/HDstory4.html

The first step in my evaluation was to fire the ammunition in a pressure and velocity test barrel from my machine rest over the Oehler System 83.

 

[weeklycigar]

path of the bullet

doesn't the projectile make a screw - type path through the air?

 

[Swampy]

doesn't the projectile make a screw - type path through the air?

Uh... no.

There is a certain amount of precession because of the high spin rate, but it is never so much (At least in any projectile to which the term "accurate" could even remotely be applied.) that the center of the precession moment and the cg of the bullet are more than a small fraction of the bullets diameter apart. IOW, the precession exists, as shown in ultra slo-mo video, but not in any truly measurable amount that shows up on a target.

Best to all,
Swampy

Garands forever

 

[jbech123]

So a rifle capable of, say, 3/4 MOA at 100m is not necessarily capable of 3/4MOA at 900m?

In pure theory it is, but since that ideal is never present in the real world, the question is by how much will all the factors that people have mentioned affect the end result. In my experience, wind (or my inability to read it properly out to 1000yards), is the main reason my 1/2 moa rifles do not shoot 5 inch groups at 1000.
To make things more confusing, I used to have a rem 700vs in .308 that would consistently shoot better from an MOA standpoint at 300 yards than 100. To make a long story short, It shot just under an inch at 100 and I could really never get it to do much better than that at 100, but would still be right at an inch at 200, and about 1.25" at 300. A few times when I did my part I had 300 yard groups under an inch. Made no sense to me. I posted around about it and some people mentioned the bullet "settling down" after the first 100 yards or so could be causing this. Not very scientific of an explanation for sure. It was however very repeatable, I even let a friend of mine test it out and he ended up with similar results. I was newer to shooting then, and I never shot it past 300 to see how far this would hold true for. I don't own the gun anymore. I know, why the hell would I sell a rifle that consistently groups ~1 inch at 300 yds with factory federal GMM.

 

[hak]

the point to take away

is that it's a 60th of a degree (or can be expressed in radians) as mentioned above. it's an angle, not a linear dimension.

does it come out to a bit over 1" at 100 yards? yes, but understand why and it makes plenty of sense.

it also gives you ideas on why mil-dot vs. moa, and why each school of thought has it's reasons. (mili-radian vs. minute of angle) 360 degrees x 60 minutes per degree = 21,600 'slices'. 6.2832 radians per circle, 'mili' = / 1000 or 6283 slices. sometimes more slices are desireable (in ranging, estimating, executing holdover or making adjustments), sometimes not (military DM ranges, speed of engagement, etc)

as someone who was researching if either is 'better' for their first 'good' scope, i came away with: a lot depends on what the shooter learned on and is most comfortable with. and that mil reticle and mil turrets weren't common on < $1000 scopes a few years ago. my only sure 'take away' was that i didn't want mil-reticle and moa knobs, b/c then i DO think of them difference as "'inches at XX yards". i'd rather stay in one camp, reticle + turrets.

i came across this a few weeks ago and found it helpful:

http://www.scribd.com/doc/4617008/Mils-and-Moa-Simplified

but on these forums, i find that IPHY (inches per hundred yards) is the more 'correct' way to express the linear "shooters MOA" mentioned above.

 

[MCMXI]

It shot just under an inch at 100 and I could really never get it to do much better than that at 100, but would still be right at an inch at 200, and about 1.25" at 300. A few times when I did my part I had 300 yard groups under an inch. Made no sense to me. I posted around about it and some people mentioned the bullet "settling down" after the first 100 yards or so could be causing this. Not very scientific of an explanation for sure. It was however very repeatable

I suppose it's possible that a bullet could become more stable in flight at a given rpm and/or resonant frequency. However, I have a theory about this and I wonder if it's got more to do with your optics and how you shoot. Many shooters crank up the power on their variable scopes even at 100 yards where every tiny movement shows up. This has the effect of making it mentally hard to pull the trigger since the reticle appears to be moving around on the target. If you back off the power to where the smallest movements are undetectable or at least less noticeable, it's apparently easier to stay on target and thus it's easier to pull the trigger. So now I'm wondering what magnification you used at 100 yards and 300 yards. This is just a theory and certainly not a criticism of you or any other shooter that has a high powered variable scope. What do you think?

 

[MCMXI]

as someone who was researching if either is 'better' for their first 'good' scope,

I'm a bit confused ... as far as I'm aware there isn't a choice. Mil dot and TMR reticles are calibrated in miliradians whereas all adjustments are MOA.

 

[hak]

"I'm a bit confused ... as far as I'm aware there isn't a choice. Mil dot and TMR reticles are calibrated in miliradians whereas all adjustments are MOA"


"TMR" = tactical milling Reticle? i'm not familiar with Leupold stuff. or a more general "tactical military reticle" ?

what i mean by a choice is: my choice #1: moa reticle with moa knobs (ie: 1/4 MOA clicks, or 1MOA clicks). vs. choice #2: a mil-dot reticle with 1/10th mil-dot knobs.

what i wanted to avoid is what you said (mil-dot scope and MOA clicks). i'm sure a lot of people dont mind it, but if i'm starting fresh, i wanted EITHER moa/moa or mil-dot/mildot, not a mildot reticle with moa knobs/adjustments.

(i chose: http://www.nightforceoptics.com/RETICLES_OVERVIEW/RETICLES_DETAIL/reticles_detail.html#npr1 an MOA reticle and the scope with Zero stop MOA knobs) instead of the mil-dot one with mildot knobs.

so: "Mil dot and TMR reticles are calibrated in miliradians whereas all adjustments are MOA" not on what i chose, by design.

 

[jbech123]

1858:

So now I'm wondering what magnification you used at 100 yards and 300 yards. This is just a theory and certainly not a criticism of you or any other shooter that has a high powered variable scope. What do you think?

The scope was a 6.5-20x, and yes I did have it cranked up to 20 at all yardages. I read somewhere that unless there is a compelling reason like mirage, it is best to use a variable scope at the same setting(most likely highest) for the best consistency. I'd say your theory could definitely have some meat to it. I use a fixed 10x for eveything these days, which could be why I don't see this type thing any more.

 

[MCMXI]

hak, hey thanks for the link ... I had no idea that MOA reticles were available and I can certainly see the benefit since windage and elevation adjustments are typically in MOA.



jbech123, since you don't have the problem with the 10x maybe we're on to something. I was informed by an "experienced" shooter at the range that the 77 grain SMK HPBT bullet I shoot in .223 is "more accurate" at 200, 300 and 400 yards than it is at 100 yards ... for the supposed reason that you mentioned. I know enough to know that I don't know enough if you get my meaning so I have no idea if this is true. Intuitively it doesn't make sense but who knows?

 

[Lon371]

While I know this is an ollldd post. I dont see where my pie plate is in any of the equations!

I knew that math teacher was crazy!

Thanks for the break down guys.

 

[Dodahdude]

"STOP", can't we all get along........

 

[Zak Smith]

No need for thread resurrection with no added information.