MOA misleading

B

Blue Duck357

New member
Maybe it's just me, but it's getting to be a pet peeve of mine when people proclaim that thier rifle will shoot 5 inch groups at 500 yards because it shoots 1 inch groups at 100. This "My rifle shoot's 1 MOA" or "1/2 MOA" is just becoming the new in phrase and I'm not sure it has any basis in reality.

My Remington 700 30-06 with 150 grain bullets shoot's around a minute (one inch) at 100 yards around three inches at 200 yards and over 9 inches at 300 yards so is it a 1, 1.5, or 3MOA rifle. Yeah some of thats me, but not all of it, as with a 180 grain loads I can shoot it about 3/4" at 100 2" at 200 and around 4" at 300 yards.

Apparently my rifle is more the rule than the exception as I've read it's common for accuracy declines too take place in a not very symetrical manner. In the same vein I've read that some long range 1000 yard loads don't really group all that well at 100 yards, but then stabilize out at and preform very well at the 1000 yard target.

Just getting this annoyance off my chest and wondering if anybody else has run into this or has some info on it.

Thanks Blue Duck
 
Yes, Its quirky

My 80 gr SMK load out of my AR15 groups better at 300 than 100 yards! I frequently get 1/2" groups at 300 yards where 1" is the best at 100.

Why? Stability. This bullet is almost perfect for the 1:7 twist barrel. Bullets react to external forces (wind, gravity etc) in a way that tends to affect their precession angle. The flight patterns are quite complex and somewhere out there in net land (I believe its from a Teutonic chap)is an on-line Java routine that will map the flight based on bullet, SD, BC, initial velocity and twist rate. Its quite odd.

I have initiated a global search and will report if found.

kj
 
Well, folks have been known to extrapolate beyond the data and run off baying at the moon--when they'd be better off remaining silent...

The standard, for decades, is whatever MOA at 100 yards one shoots; this is merely a comparison against other rifle packages' performance at 100 yards. Like you noticed, one MOA (+ or -) at 100 yards does not mean the rifle will shoot to the same angle at longer distances.

For forty forevers, the standard measurement for muzzle velocity for most rifles was taken from a 26" barrel. Now, you gotta read the fine print in many loading manuals. I have no objection to using different lengths, but it makes it difficult when one person is talking 26", and the other fella is comparing it to a 20".

That just the way people are, and it's pointless to worry about it.

:), Art
 
I probably shouldn't say this...but...

If a rifle shoots better at 300 yards than it does at 100 yards, it ain't the rifle and "stability" has nothing to do with it. Perhaps the shooter's "concentration" gets better at 300 or the target size is more appropriate for a better sight picture but bullets in flight don't spontaneously stabilize and correct their flight to produce better MOA groups at increased distances.

I always qualify my gun/ammo combinations, i.e. this is a 1/2 MOA gun out to 200 yards or it's a 1 MOA performer out to 400. As the distance increases so does the spread. The ammo isn't perfect, neither is the bore or the sight. The further you go the more the errors accumulate and the rifle and load will give it up at some distance. Some at 200 yards...some beyond 1000!

Just my opinion but I'll stake my reputation on it!

Mikey
 
Mikey, I know it's not a rifle but I have seen slow motion pictures of arrows leaving a bow at all kinds of weird angles then straightening out to hit the same place on a target maybe the same thing. This is apparently a well accepted phenonmenon in 50 caliber shooting. Shooting times also did a story on handguns bullets at extended ranges when fireing from a ransom rest that showed some loads being more accurate at 100 yards than at 50, so I think our .223 shooter may be right on this. But your reputation will always be fine by me :D

Regards, Blue Duck
 
Go to "How do bullets fly?" at: http://www.povn.com/~4n6/index.htm
Then go to "bullets at short ranges" and you'll see the self-correcting initial yawning motion of bullets at the first few meters (most of them in a very short distance, less than 100m). Maybe the 50 BMG bullets take longer to damp this initial yawning?
Also look at the very fast stabilizing effect of some handgun bullets, and the anomalies of dinamically unstabilized bullets that increase the yawning with distance.
Theoretically it is impossible to shoot 1 MOA at 100 yards and 0.5 MOA at 200, but there may be many factors involved in a test that sometimes contradict this. In any case, if you take away as many variables as you can (for example in benchrest competition) the rifles always shoot smaller MOA fractions at the shorter distances, as logic would have.
 
Sometime back in the 60's (yea I know ancient history to you youngsters{not you Art} :D)) The American Rifleman had a great article on the same subject we are discussing now. They also had some fine charts and drawings showing the initial yaw and gyroscopic progression and how the bullet that the article was written about "settled in" after a bit and flew true. The ammo the article was written about was the USGI 173 grain Match in 30-06.
 
This is interesting stuff. I've never really considered the possibility of a bullet becoming more stable during flight. Guess I always assumed that a bullet's rotation would never be faster than at the muzzle, and that slower rotation (resulting from energy loss over time) combined with decreasing speed (resulting from friction) would lead to less stability -- if anything.

I have read that bullets suffer instability due to buffeting as they slow down through the sound barrier, and there is always the problem of cross-winds. Otherwise, I am fairly clueless to the physics that affect bullet stability down range.

If anyone comes up with more info, please post the source(s) so that I can look it up.

Thx.
jbgood
 
jbgood, one of the advantages of a boattail bullet is when it does slow to the trans-sonic speeds the boattail design causes less drag and buffeting.
 
I'm an old bow shooter (besides just being old) and I'm well aware of the yaw experienced in arrow flight. It is especially pronounced in a poorly tuned bow but, if the archer is extremely consistent, good target groups can still be fired. The key is consistency because that causes each arrow to follow nearly the same path. While it can cause arrows to strike short range targets with the shaft at an angle, the points are at nearly the same spot and the angle of penetration is almost identical for each arrow. The fletching reacts with the air to eventually straighten the arrow in flight.

I don't doubt that this same type of phenominon can cause bullets to yaw (and correct within some distance), which could produce elongated holes in short range targets, but the path of each shot would have to be very consistent to get good accuracy at distance. I still don't believe a group of five shots could travel different enough paths to cause a 1 MOA dispersion at 100 yards and then change path and come together for a 1/2 MOA dispersion at 300. In my "old fart" mind it just ain't happenin'!

Mikey
 
MOA's

Gent's,
Having been a victim of this many times, I can assure you it does happen.........
I have rounds that shoot sub 3/8" groups at 100 yds, and will open up to well over a minute at longer ranges.
I have loads that will shoot sub .375 moa @ 100, and will shoot sub .250moa @ 500 yards.........
Reason one is yaw, and load development.........
If one is loading for rounds that he expects to perform at long range, then the minimum range to DEVELOP those rounds is 300 yards........
Yaw,occurs as a projectile leaves the muzzle, and then stabilizes at a certain distance, it has then reached the point of what is commonly refered to as "going to sleep",it will then (if range is long enough), tend to Yaw again when it slows down to below transonic speed......each bullet design differs, and acts, and reacts accordingly.
Blue Duck, your '06, could concievably shoot to, or within the envelope you are stating, IF you changed your load, (i.e.)brass, powders, primer, bullet type etc..........
There are as most of you know, so many variables that you would have to be a ballistics scientist to even begin to explain the phenomenom, much less to say you know the exact reasons.
We know they happen, and we can correct some of them , with trial and error.........(:@)
 
Tshoes, you're right...

From the Sierra Infinity Manuals CD, 4th.Ed., Exterior Balistics, chapter 4.6 (highly recomended reading) :
"....precessional motion (or coning) and nutational motion may result from "tipoff" forces which occur when the bullets exits the muzzle of the gun...(they) usually damp out as the bullet flies, but only after 100 yards or so."
"It turns out that coning motions are worse for long, slender, heavy bullets than for shorter and lighter bullets" (that's why benchrest bullets are short).
"If the bullet is coning, it presents an effective area that is larger than the true cross sectional area of the bullet ...to produce a larger drag force ...it therefore appears to have a lower BC".
They show very interesting results from tests, for example a 190 gr MK HPBT tested over 50 and 250 yards showed clearly that the coning had not damped at the shorter range and did at 250 yards. They also have experiments showing the effect of twist rate in this dampening of the coning motion.
A rifle can (usually does) shoot tighter MOA groups at shorter ranges, but a relatively small difference can be had in the opposite direction, .375 MOA at 100 vs .25 MOA at 300.
Tshoes, are you aware of any rifle "improving" after 200 or even 300 yards? That would seem highly unlikely.
 
The initial "coning" motion of the bullet is why shooters often see some keyholing at short ranges and also why penetration is greater at longer ranges after the bullet has stabilized. This is hard to grasp if one has become used to the idea that penetration is solely a matter of velocity. One gunzine guru even wrote that greater penetration at 100 yards than at 50 yards proved that bullets speed up in the air!! Maybe it was from the hot air coming out of his mouth.

Jim
 
"One gunzine guru even wrote that greater penetration at 100 yards than at 50 yards proved that bullets speed up in the air!! Maybe it was from the hot air coming out of his mouth."

Jim, I don't know what he was drinking, but whatever it was I do not recommend him either driving or shooting after drinking it! Speed up! That is one of the Dumbest ones I have heard lately!
 
Reuben

It all depends on the LOAD, your rifle plays a significant part in accuracy....but I hold the LOAD has just as much or more to do with the accuracy, and at different ranges.

And, yes, as in the previous post if you ever shoot the 175's BTHP's @ 100 yards, you will notice they don't "punch", really clean cut holes........

The same round at 300, 500 will look like a laser cut the hole.......reason ..it has stabilized.

As in my previous post, I have a load that will shoot sub .375 moa @ 100 yds.

Kick this same round to 500 yds, and it shoots sub .250 moa, this is in essence what you are asking....or am I missing your point/question???/
 
Tshoes, that's exactly what I was talking about, the only thing there's left to ask is the minimum distance the load needs to "put the bullet to sleep". I would guess that for even the longest bullets the initial yaw would be damp out at 200-300 yards max., and from there on the grouping capability could not be improved. What is the minimum distance your 175gr. MK HPBT load needs to shrink to .250 MOA?
I've shot heavy bullets before in my 308's, but I've never realized the difference in the holes at the shorter distances (100 yards); I'll have a closer look now. The initial coning angle (at the muzzle) is only about to 2.0 deg. or less, and it damps out quickly, so it is never very large.
 
Heavy Bullets

Reuben, the weight of the projectile really doesn't have much, if anything to do with it........it's the angle of the boatail, and the design of same........some bullets are designed to work and fly differently than others.
The 175's, are what I have the most experience with, and I agree with you........after 200 yards, there will be no significant change for the better...it will have gyroscopically stabilized by then or before.
 
This would be an excellent topic to bring up in an engineering physics class! Too bad those days have passed me by......it could have been an interesting lab experiment! ;) However, I guess I can reference my physics books and check out what they say about angular velocity.


kgs.
 
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