Accuracy At Different Ranges

[Bart B]

Thought I'd sample reader's thoughts on this one. Who knows what may show up for answers?

Let's say a given rifle and ammo shoots 1 inch (one minute of angle, or moa) at 100 yards.

What size in moa will the group be every 100 yards down range to 1000 yards?

 

[davewilson]

if it's set up to shoot long range i'd say probably .5MOA at 200, and plus about 5-10% every 100 yards after.

 

[Guest]

Bart

Seems to me when we tested our Palma rifles.....we'd shoot from 800 yds. and if ten rounds would go into 1/2 the X ring...that was acceptable! Those rifles may....or may not have shot exceedingly well from 100 yds. off a bench but there's nothing firm that says that they would have because of the intricate variables involving bullet stability! One would think that if a certain ROT was utilized that all would be well but each rifle is an entity onto itself and what works with one....may not work with another! This goes for reloaded ammo also! Johnie Franklin had a rifle one year that wouldn't shoot worth a "fonk" UNLESS....the ogive was backed off 0.050" off the lands whereby yours/mine....wouldn't have kept them on the shxthouse wall!! But to answer your question more plainly.....if I've got a rifle that I think will shoot 1/2 MOA at 100 yds. I'd expect it to at least hold 2/3 of the ten ring at 1000 and I'll let God and the law of averages deal with the X count!! And the only way to tell what one is capable of is to put a rifle into a very well made "fixture"....pick a day that is good.....and see what comes up on the target face downrange! When I was with the Army Team....we had M-14s that would shoot ten shot groups into 4" from 600 yds. and that my friend is good ammo; Lake City Match it was!! /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif

 

[sambo3006]

Just for the sake of correct terminology, one MOA roughly corresponds to one inch at 100 yds (I think it is ever so slightly larger than one inch). So one MOA would be roughly 2 inches at 200 yds and so on. I have not shot at ranges farther than 400 yds, but even at that moderate distance, a 0.5 MOA gun at 100 yds does not necessarily stay in 0.5 MOA @ 400 yds. Lots of factors. I hope to find a spot to shoot farther, as I have been wondering basically the same thing as you for a particular rifle.

 

[Bart B]

Sambo3006, a trig minute of angle at 100 yards is 1.0472 inches. But a shooting minute of angle at 100 yards is exactly 1 inch. That was decided many years ago when sight radius on most target rifles was 30 inches and a 40 thread per inch lead screws in the rear sight was standardized. One turn on the windage or elevation knob moved the sight .025-inch; one-third turn moved it .008333 inch. 30 inches divided by 3600 (number of inches in 100 yards) equals .0083333-inch.

Most USA NRA smallbore and highpower rifle targets have scoring ring diameters based on this axiom as does most US made aperture rear sights' adjustments.

 

[sambo3006]

[ QUOTE ]
if it's set up to shoot long range i'd say probably .5MOA at 200, and plus about 5-10% every 100 yards after.

[/ QUOTE ]
Bart, this is what I was mainly getting at as far as clarifying the concept of the MOA. Obviously if the gun shoots 1 MOA @100yds, it shouldn't do 0.5 MOA @ 200(No offense to Dave Wilson). I didn't know the origin of how the shooting MOA came about, that is interesting. I guess I could have looked up the exact value of the minute of angle, but I'm too lazy! Thanks for the illumination! Sam

 

[davewilson]

Sam, you obviously haven't shot much at long range to not understand that a gun can shoot better moa at 200 than it can at 100.i once saw a 1000 yd bench gun almost thrown away on it's first outing because it shot around 2" at 100 yards.a young fellow who just started working there asked if he could shoot it and they said go ahead, it's a piece of sh. as the rest laughed at him he took a target out to 300 yards.the guy that built the gun wanted to shoot it again when the kid put 5 in less than an inch.they repeated this a couple of times and confirmed that it was dogpoop at 100 yards.but somewhere between 1 and 300 yards they went to sleep very well.

 

[sambo3006]

Dave,
Not trying to ruffle any feathers or get personal. You're right, I have not shot past 400 yds (no place available). As far as the "put to sleep" thing, I have heard this before. I guess that I can't believe this until I see it (I am from the Show Me State-ha, ha). It would seem to defy physics (maybe physics isn't the right term but for lack of a better one). Isn't a bullet going to follow a straight line of flight horizontally if no effect from the wind? The slightly divergent paths of bullets in a group would seem to disperse them farther apart as the distance from muzzle increases. A bullet would have to curve in flight for the group to get tighter at longer range. I'm not saying that the put to sleep phenomenon doesn't exist since many people talk about it, I am just curious as to how and why it occurs. I have shot 5 or 6 of my rifles out to 300-400 yds and haven't experienced it. This is a fairly limited sample, however.
I am fairly new to getting serious about long range shooting and love this site for learning from others with more experience. Regards, Sam

 

[ss7mm]

sambo3006:

Where I have seen this is mostly in heavy for caliber bullets. It doesn't always happen but under accurate and careful testing it does show up.

My take is that when this heavy for caliber bullet is traveling down the bore of the rifle it is forced to rotate around the axis of the bore. This is not a problem while the bullet is inside the barrel but after it exits the barrel it wants to try and rotate around its own center axis. Theoretically the center axis of the barrel and of the bullet can't be exactly the same. When the bullet tries to "stabilize" and rotate round its own axis it can't happen immediately. Sometimes this can take up to 200 yards or more for the bullet to fully stabilize, spin around its own center axis and be happy. Some people call this rotational stabilization, "going to sleep".

I think that when you have an ideal setup, and by that I mean a premium barrel with the optimum twist for your bullet, a premium, heavy for caliber bullet properly made and a velocity/load combination that is sweet with this bullet, that you will not notice it as much but that is just personal experience.

When you say you have shot 5 or 6 of your rifles out to 400 yards are you using heavy for caliber bullets or lighter weight bullets? My thoughts and experience is that heavier for caliber bullets do this more readily than light weight bullets. I also believe a quality bullet will exhibit it to a lesser degree. Are you shooting one group or multiple groups per yardage? Do you compare same exact load/gun at 100, 200, 300, 400 etc. or just 100 and 400? Just curious.

Given this phenomenon you can see how Dave's .5moa at 200 can and will happen with a 1moa group at 100 yards. Like I said, normally I have found, with heavy for caliber bullets, that stabilization is good around 200 yards, give or take. I do believe that with a gun composed of quality components and with a shooter that has a lot of time behind that gun, that Normally you can also take into consideration what Dave said about a slight increase in groups, per 100 yard increments, on out to 1000 yards and beyond. I would believe this is caused more by the shooter than the gun. You just can't see and hold as well at 1000 yards as you can at 100 yards, not day in and day out at least. Sure you can and will get groups at longer ranges that go against the normal incremental size increases but this will not be the norm. You have to go by what you, and your gun, can average, under all conditions, at each range. In answer to the original question, I would say that the only way you can know what your gun, and you, can do at 100 yard increments from 100-1000 yards, and beyond, is to shoot it and see. Otherwise you are only going by what theoretically can or will happen.

When the shot counts and your data has to be exact, it had better come from field experienced data or you will be guessing to a certain extent.

 

[sambo3006]

Most of my shooting has been with medium bullet weights i.e. 100 gr .257, 129 gr 6.5mm, 140 gr 7mm, 150 gr .308, 225 gr .338. Thanks to finding this site, I plan to start using heavier bullets. I have not done extensive shooting at those yardages (a couple of times per gun). My groups tend to be a little larger proportionately at longer ranges, probably as you stated due to shooter, not gun. Your explanation does seem to make sense. Bullets are not perfectly manufactured.
Thanks for all the info, guys. I guess it all boils down to shooting your gun at different ranges to see where and how it shoots.

 

[Guest]

Read here:

http://www.tuffsteel.com/store/Ballistics/bullfly/fomo.htm#header_forcesmoments

 

[Bart B]

For those who think short range groups can be larger in MOA than longer range groups, please explain the following.

How does a bullet that's far away from the center of several previous trajectory paths know which way to change its trajectory so it'll be closer to the center of previous trajectory paths further down range?

In order to make groups smaller in MOA at a greater range, somehow it must know whether to go up, down, left or right or a combination of two of these directions.

 

[davewilson]

the reason is "yaw" not a southern term i might add.when a bullet exits the barrel this sudden unsupported state causes the bullet to fishtail but not in a sideways motion but in a circular corkscrewing path.the back of the bullet is always farther away from the centerline of travel than the front of the bullet is.this is how the bullet comes back to the same centerline of travel.i once shot at targets placed at 35,75,125, and 200.took 1 shot at each target and then another range until i had 4 shots in each target. my group size at the first 3 ranges was very close to .75" and 200 was around an inch. i agree with Dick, the better everything is matched up, the less it will yaw in the begining and the better it will be downrange.