Hi guys, If this has been covered just tell me.

I notice on the site lots of people saying that they can shoot a .4 inch group (or better) at 100 yards so the rifle can shoot a 4 inch group at 1000 yards. At first i accepted this but I'd like some feedback as IMO this is false.

A .4 inch group (100 yards) with a .30 cal is actually a .7 inch group (100 yards). We minus the calibre from the initial group, right? (.7 - .30 = 0.4)

It stands to reason that to infer the 1000 yards group we really should be going .7 x 10 = 7 inch group. Then minus the calibre from the 7 inch group, giving us a 6.7 inch group at 1000 yards.

Opinions?
Cheers.
Matt.

Matt

Groups are measured center to center of the widest shots. That method allows the direct comparison of group size without regard to caliber.

What you described refers to measuring the extreme spread from outside to outside and subtracting one bullet diameter. Some feel that is an easier method since you do not have to guess where the center of each shot is. Also, that method works best when measuring one-hole groups where you cannot discern the individual holes.

One MOA is actually 1.047" at 100 yards, so close to an inch that shooters, for all practical purposes, consider it an inch. 1 MOA at 1000 yards is 10.47 inches but most shooters consider it to be 10.00 inches. .47 inches is insignificant at that distance.

In theory at least, a rifle that shoots 1 MOA at 100 yards should shoot 1 MOA at all distances but it doesn't work out that way. There are environmental, sighting errors, and other factors that come into play - the farther the distance the more they influence group size.

Ray

Sorry, my subject is poorly worded. I've accidentally asked two questions.
The Subject question you've definately answered but the other i'm not sure that you have.

I'll add to the main question, "In a 'Perfect World' and in a vacuum". That way the shooter is perfect, the gun is perfect, and there is no wind.

C'mon Ray - we all know your groups get smaller as the distance increases


Here we go again (ain't I a stinker?)

Scarab,
I believe that the IBS 1000 yard record group for 5 shots in the light gun class is 1.397". I think that may be a little smaller than 1" MOA.
They ain't no perfect shooter and they ain't no 1000 yard vacuum anyplace close.
Butch

quote:

Originally posted by butchlambert:
Scarab,
I believe that the IBS 1000 yard record group for 5 shots in the light gun class is 1.397". I think that may be a little smaller than 1" MOA.
They ain't no perfect shooter and they ain't no 1000 yard vacuum anyplace close.
Butch

Ha Ha, yeah, yeah, okay. All i was saying is that, gun and shooter apart, the math of inferring a group past where it has actually been measured seems to go astray occasionally.

I'll put it you this way. If you shoot a .2 at 100 yards, do you say that it will shoot .4 at 200?
1.397" at 1000 yards? I can't think of words for that.

I think there's some issues folks aren't considering as to group sizes as range increases. None of them have anything to do with atmospheric or shooting conditions. They have everything to do with exterior ballistics.

First, all the bullets fired for a group don't leave the muzzle at the same speed. The faster ones will drop less down range than the slower ones. Even if each fired bullet has exactly the same drag (ballistic coefficient), this velocity spread causes vertical shot stringing. A 100 fps spread in velocity can cause a 2/10ths inch vertical shot stringing at 100 yards (2/10ths MOA) but 45 inches at 1000 yards (4-1/2 MOA).

Second, assuming we could get every bullet to leave the barrel at exactly the same speed, the small variance in drag across all the bullets comes into effect. New bullets are not perfectly balanced and firing them imbalances them a bit more. This means they'll all wobble a tiny bit in flight. And that means their drag will vary a tiny bit; typically 1 to 2 percent for the very best ones we can get. Which means that the ones with more drag will drop more for a given down range point; those with less drag will strike higher.

It won't take long for folks to run their favorite ballistic software and note the vertical shot stringing that will occur with velocity and drag spreads at different ranges.

One can also see that if there's just a slight wind, that will drift bullets further per yard of travel as range increases. But most of the group size increases is due to muzzle velocity and ballistic coefficient spreads.

Back in the late 1800's, a minute of angle for shooting was defined as 1 inch at 100 yards. Mechanical sights were based on a 30 inch radius between front and rear sights. Threads on the leade screws on the sights were 40 tpi and one turn moved the sight .025-inch. That's 3 MOA for a 30 inch sight radius. Telescopic sights had their bases 7.2 inches apart and the rear base with adjustments moved the scope at that point .002 inches for each 1/4th MOA change.

Don't confuse trigonometry MOA with shooting MOA; they ain't the same.

I think there's some issues folks aren't considering as to group sizes as range increases. None of them have anything to do with atmospheric or shooting conditions. They have everything to do with exterior ballistics.

First, all the bullets fired for a group don't leave the muzzle at the same speed. The faster ones will drop less down range than the slower ones. Even if each fired bullet has exactly the same drag (ballistic coefficient), this velocity spread causes vertical shot stringing. A 100 fps spread in velocity can cause a 2/10ths inch vertical shot stringing at 100 yards (2/10ths MOA) but 45 inches at 1000 yards (4-1/2 MOA).

Second, assuming we could get every bullet to leave the barrel at exactly the same speed, the small variance in drag across all the bullets comes into effect. New bullets are not perfectly balanced and firing them imbalances them a bit more. This means they'll all wobble a tiny bit in flight. And that means their drag will vary a tiny bit; typically 1 to 2 percent for the very best ones we can get. Which means that the ones with more drag will drop more for a given down range point; those with less drag will strike higher.

It won't take long for folks to run their favorite ballistic software and note the vertical shot stringing that will occur with velocity and drag spreads at different ranges.

One can also see that if there's just a slight wind, that will drift bullets further per yard of travel as range increases. But most of the group size increases is due to muzzle velocity and ballistic coefficient spreads.

Bart

Nitpicking to be sure, but I've never heard of a "shooting MOA" and a "trigonometry MOA". A MOA is a MOA, 1/60th of a degree. Because it would be very difficult to graduate sights to a true MOA, shooters over the years have come to accept it as 1 inch at 100 yards, making life much simpler.

It would have been much easier if shooters had adopted the mil (1/1000) but it's way too late for that now.

I can't say that I agree completely with all of the exterior ballistics that you talked about, but ballistics is nothing more nor less than physics, Mother Nature's rules that are set in stone and can't be changed no matter how hard we try. The problem is that real life doesn't always appear to conform to the rules - such as that load that has a 100 fps spread in velocity and yet still shows very little vertical at the extreme distances.

I have shot enough 1000 yard matches to have formed my own opinion of what is going on. It boils down to two things.

1) A lot of it is pure $hit ass luck.

2) Sometimes the wind will blow them out and sometimes the wind will blow them in.

Ray

Ray,

Considering the mil (milliradian) has four standards around the world, that's not to easy to use for gunsights.

There are 2000Ï€ milliradians in a circle. So a milliradian is just over 1â„6283 of a circle. Each of the definitions of the angular mil are similar to that value but are easier to divide into many parts. Here's the four world standards:

1â„6400 of a circle in NATO countries.

1â„6283The “real†trigonometric unit of angular measurement of a circle in use by telescopic sight manufacturers using (stadiametric) rangefinding in reticles.

1â„6000 of a circle in the former Soviet Union and Finland (Finland phasing out the standard in favour of the NATO standard).

1â„6300 of a circle in Sweden. The Swedish term for this is streck, literally "line". Sweden has not been part of NATO nor the Warsaw Pact. Note however that Sweden is changing its map grid systems and angular measurement to those used by NATO, so the "streck" measurement is about to become obsolete.

Which one of these four best qualifies it for use on rifles and pistols?

It's easy to make sights move any amount of angle. Third-grade math's all that's needed. The iron sights I mentioned earlier moved the rear sight 1/3600th of the 30-inch sight radius so one minute of them would move impact 1 inch at 100 yards. There's 3600 inches in 100 yards. To use a rear sight with its leade screws at 40 tpi and three "minutes" per revolution, just change the sight radius to 28.647890160552565351356763198219 inches then bullet impact would move exactly 1.047197536428328546947470696664 inch which is what one "trig minute" of angle subtends at 100 yards.

Not to mention that all the NRA highpower NRA smallbore targets' scoring rings are based on even inches; which is why sights in the USA used the mechanics I mentioned as they are typically used in even increments or fractions of 100 yards.

Sure, we could use the US military mils instead of what's popular. Imagine wanting to make a 1/2 inch change in impact at 100 yards with sights moving 3.6 inches per mil for each hundred yards of range.

quote:

Originally posted by Cheechako:
The problem is that real life doesn't always appear to conform to the rules - such as that load that has a 100 fps spread in velocity and yet still shows very little vertical at the extreme distances.

The Brit's proved back in the 1930's that their SMLE rifles shooting ammo with huge muzzle velocity spreads did so well at long range 'cause the muzzle angle was higher for low speed bullets and less of an angle for high speed bullets. This is called positive compensation and their long range groups subtended smaller angles than short range ones. But they preferred Mauser 98 based rifles for short range matches 'cause there was no compensation with those front locking actions. Only the rearlocking SMLE's had compensation and were more accurate than the Mausers at long range.

The US Army and US Marine Corps rifle teams learned that their M14 rifles did the same thing, but to a lesser degree. Their reasoning was that with the gas port about mid point of the barrel on the bottom, higher port pressures that produced faster bullets pushed up on the middle of the barrel forcing the muzzle to point a bit lower as the bullet exited. That way, compensation would occur for faster bullets. Just the opposite would happen for slower ones with lower port pressure, the muzzle would be at a higher angle so those bullets would strike closer to center.

quote:

Originally posted by Bart B.:
... It won't take long for folks to run their favorite ballistic software and note the vertical shot stringing that will occur with velocity and drag spreads at different ranges.

On vertical stringing, i've seen 70gn Sierra out of a .223 Rem (handloaded) have a vertical string of about 2 inches at 100m. Side to side there was maybe 1cm. The loads were compacted. Could your above paragraph explain this?

quote:

Originally posted by Scarab:
On vertical stringing, i've seen 70gn Sierra out of a .223 Rem (handloaded) have a vertical string of about 2 inches at 100m. Side to side there was maybe 1cm. The loads were compacted. Could your above paragraph explain this?

Not if your rifle's a front-locking bolt action rifle. That only happened with bolt action rifles that have rear-locking bolts; the SMLE for example.

With that much vertical stringing, I think there's something else causing it. If that happens once in a while, the most probable cause is different rifle-holding pressures by the shooter. Especially if the rifle's fore end is resting on a harder surface. Or if the barrel's pressing down, hard, against the stock's barrel channel

I'd try factory ammo, then see what happens.

One minute of angle is 1.047 inches at 100 yards. One minute of angle is 10.47 inches at 1000 yards.

Bart:
Please explain to me how a difference in position of locking lugs on a bolt affect the "muzzle angle" of a rifle at the time of bullet's exit?
I just can't wrap my head around this one.
I can see a lot of strange flexing of the bolt. But I don't see how this will make the muzzle behave differently than a muzzle of a front lugged bolt action.
Thank you for your time
Sincerely
muck

Could put torque on the front of the bolt, where the bullet is, making it jammed sideways in the chamber?

My understanding of the well documented Lee Enfield shooting higher point of impact with LIGHTER loads is. The longer barrel time causes the bullet to exit the muzzle as the barrel/muzzle has started it's upward climb in the primary figure eight vertical oscillation. My question is how would a difference in locking lug location cause or affect this phenomenon. Or am I missing it?
Just want to know.
Tyler Kemp: The motion you suggest seems to be too erratic to provide good accuracy. Let alone consistently higher impacts on target.

muck

Extensive scientific study has concluded that closing your eyes just as you jerk the trigger helps introduce randomness into groups. Engineers are still studying the phenomenum.

muck

While I certainly defer to the mathematicians in the crowd, I understand the MOA to be approx 1.047 or so at 100 yards (one minute of angle, or 1/3600 of a circle (sixty degrees times 60 minutes). Miliradians of whatever flavor are irrelevant to the thread, I think.

As a fair HP shooter, I have learned that a tiny test group at 100 yds does not equate necessarily to a similarly sized group at range.

If the rifle, ammo and shooter all were to be able to hold accuracy to 1 MOA, then a group at any given range should proably wind up to be approxitmately 1.73 inches per 100 yards of range {(Root sum of squares) or 1SQ+1SQ+1SQ= 3, Then take the SQRT, or ~1.73".

If we could hold less than 1 MOA, shoot ammo of less than 1 MOA out a of a rifle capable of shooting less than 1 MOA in conditions that allow less than 1 MOA of variability, then we could shine. As it is, we can only control (to some respect), the shooter, the gun and the ammo.

Rather than a 3-5 shot groups as an indicator (not statistically significant) we would do better to shoot multiple 10 -20 shot groups to get a true feel for shooter/ammo/weapon & conditions ablity, then expect each shot to be inside that circle every time.

My take on it, anyhow.

My NM M1 Garand in 30 US can shoot a 1 inch or so group at 100, but I can only accomplish about a 10 inch hold at 600 (10 ring is just over 12 inches or ~2 MOA), just inside the 10 ring of a MR target. If I zero properly, hold all 20 rounds just so, dope the wind correctly for each shot the rifle can clean the 600 stage. Alas, I have not yet accomplished that, yet.

God Bless and MOLON LABE

Also, when the bullet transitions from supersonic to subsonic also affects the stability of the bullet. For example, a MOA rifle at 600 yds may become a 2MOA rifle at 700 yds if the bullet goes subsonic between 600 and 700 yds.