convergence

[coola4me]

Can you explain mtnman why that would be true?  I am curious how bullit path would arc down then up.Is it Site height to muzzle?

Maybe these illustrations and quote from another website will help:

Begin quote: We have a tendency to get the "line of sight' mixed up with the "line of bore." The line of sight is always a straight line from the eye through the scope to the target. The line of bore is also a straight line from the chamber through the bore to infinity. It's plain to see these two lines are always straight, but it's common to confuse the bullet's path, which is always a curved line, with the line of bore.
It's fair to say the bullet's flight path is a down-curving line from the rifle's muzzle; it falls faster as the bullet moves forward. Now, if the sights were aligned parallel with the bore line, it would be impossible for them to ever intercept the path of the bullet which is falling below the line of bore all the time.
I have to point out here that if this couldn't be remedied, the hunter would have to aim somewhere above the target on long shots. It would be a game of guesswork. Fortunately, this dilemma can be corrected by adjusting the sights so the line of sight intercepts the bore line instead of being parallel to it.
When we adjust the sights for longer ranges, the rifle's muzzle is tipped upward when the sights are aligned on the target. This causes the bullet to pass through the line of sight a short distance from the muzzle, travel in a curved line above the line of sight, and then fall through it at whatever distance the rifle is sighted in for. Note that the bullet never rises above the line of bore. Actually, the rifle is sighted in for two distances. One a few yards from the muzzle, the other where the bullet comes back through the line of sight.
The arc of flight is not a true curve; it's an elongated arc. A rifle sighted in for 250 yards may be two inches high at 100 and three inches high at 165. The bullet then begins a downward journey passing through the line of sight at 250 yards. The highest part of the flight is called the maximum ordinate, and it usually is around two thirds of the distance to the sight in point. With today's open terrain hunting, trajectory or the arc of the bullet is something every hunter should be concerned about. The popularity of the riflescope puts hunters on watches where very long shots are possible. It's almost a waste of time to take one of these stands with a rifle zeroed in for a 100 yards. Knowing the path your bullet follows, and sighting in to take advantage of it is a sure formula for success.

[mtnman]

Maybe these illustrations and quote from another website will help:

Begin quote: We have a tendency to get the "line of sight' mixed up with the "line of bore." The line of sight is always a straight line from the eye through the scope to the target. The line of bore is also a straight line from the chamber through the bore to infinity. It's plain to see these two lines are always straight, but it's common to confuse the bullet's path, which is always a curved line, with the line of bore.
It's fair to say the bullet's flight path is a down-curving line from the rifle's muzzle; it falls faster as the bullet moves forward. Now, if the sights were aligned parallel with the bore line, it would be impossible for them to ever intercept the path of the bullet which is falling below the line of bore all the time.
I have to point out here that if this couldn't be remedied, the hunter would have to aim somewhere above the target on long shots. It would be a game of guesswork. Fortunately, this dilemma can be corrected by adjusting the sights so the line of sight intercepts the bore line instead of being parallel to it.
When we adjust the sights for longer ranges, the rifle's muzzle is tipped upward when the sights are aligned on the target. This causes the bullet to pass through the line of sight a short distance from the muzzle, travel in a curved line above the line of sight, and then fall through it at whatever distance the rifle is sighted in for. Note that the bullet never rises above the line of bore. Actually, the rifle is sighted in for two distances. One a few yards from the muzzle, the other where the bullet comes back through the line of sight.
The arc of flight is not a true curve; it's an elongated arc. A rifle sighted in for 250 yards may be two inches high at 100 and three inches high at 165. The bullet then begins a downward journey passing through the line of sight at 250 yards. The highest part of the flight is called the maximum ordinate, and it usually is around two thirds of the distance to the sight in point. With today's open terrain hunting, trajectory or the arc of the bullet is something every hunter should be concerned about. The popularity of the riflescope puts hunters on watches where very long shots are possible. It's almost a waste of time to take one of these stands with a rifle zeroed in for a 100 yards. Knowing the path your bullet follows, and sighting in to take advantage of it is a sure formula for success.



(Image removed from quote.)
(Image removed from quote.)

That is what's going on, but it can be misleading to compare the scoped rifle to the aircraft, because the scope is mounted so close to the rifle bore.

Redraw the picture with the scope mounted @ 5ft above the rifle barrel, and you'll be close to the situation presented by firing the wing-mounted guns on a P51, corsair, etc...

[coola4me]

That is what's going on, but it can be misleading to compare the scoped rifle to the aircraft, because the scope is mounted so close to the rifle bore.

Redraw the picture with the scope mounted @ 5ft above the rifle barrel, and you'll be close to the situation presented by firing the wing-mounted guns on a P51, corsair, etc...

The concept of bullet "arc" is the same regardless if its shot from a hunting rifle or a wing mounted .50cal. Line of sight (looking through the gunsite) and line of bore (down the barrel) would be the same.

[mtnman]

The concept of bullet "arc" is the same regardless if its shot from a hunting rifle or a wing mounted .50cal. Line of sight (looking through the gunsite) and line of bore (down the barrel) would be the same.

The concept is the same, yes.  The results vary tremendously.

Aiming a bullet by using a scope mounted directly above the barrel yields vastly different results compared to aiming a bullet by using a gun sight mounted several feet above the barrel (when it comes to where the bullet is in its trajectory BEFORE and AFTER it hits the "bull's eye" at whatever the convergence is set at.

With a rifle, it's off by inches (for the most part); with a wing-mounted gun it's off by feet.  With a rifle, it's "intuitive"; with the plane, it's generally counter-intuitive.  It's compounded by the long ranges as well (plus a whole lot of other factors).

[coola4me]

The concept is the same, yes.  The results vary tremendously.

Aiming a bullet by using a scope mounted directly above the barrel yields vastly different results compared to aiming a bullet by using a gun sight mounted several feet above the barrel (when it comes to where the bullet is in its trajectory BEFORE and AFTER it hits the "bull's eye" at whatever the convergence is set at.

With a rifle, it's off by inches (for the most part); with a wing-mounted gun it's off by feet.  With a rifle, it's "intuitive"; with the plane, it's generally counter-intuitive.  It's compounded by the long ranges as well (plus a whole lot of other factors).

Yes i would agree but, the illustration (borrowed) was giving a visual reference explaining bullet "arc" which would be the same with any line/bore sighted weapon.
Basically answering this quote with a picture:

Can you explain mtnman why that would be true?  I am curious how bullet path would arc down then up.Is it Site height to muzzle?

[1Cane]

Ok after rereading Karnak at least 3x I get it!  Bullit still on upward path but still low at 200yds,hits bulleye at 400 yds. Explains alot of misses at 200yds

[mtnman]

Yes i would agree but, the illustration (borrowed) was giving a visual reference explaining bullet "arc" which would be the same with any line/bore sighted weapon.
Basically answering this quote with a picture:

It would/does, but using that diagram also leads to a whole lot of confusion when it comes to gunnery and convergence settings in AH.  This is an example-

I say that if you're convergence is set at 400 Yards that your 50 Cal, and 20 MM will hit the bull's eye at the 400 yard mark.  The lighter bullet will be flatter and the heavier bullet will have more of a arc to it.  Your rounds will be high at 200 yards and low at 600 yards.

And diagrams like these (borrowed from the Trainers site) add to the confusion, because none of them show accurate trajectories (particularly for wing-mounted guns)-





The "Aim Point too close/too far trajectories are particularly inaccurate.  The "Too Far" picture should go with the "Too Close" title, and the "Too Close" picture should really be deleted, as it doesn't work with either description.  The crossing diagrams aren't bad though.

A trajectory like the one shown at the bottom is achievable, but only with certain settings.  It's not a good a "general" guideline.

[mtnman]

Ok after rereading Karnak at least 3x I get it!  Bullit still on upward path but still low at 200yds,hits bulleye at 400 yds. Explains alot of misses at 200yds

Yup, the difference is that with the "rifle" diagram, the bullet comes up through the LoS before it gets to the target, and hits the target on it's way back "down".

With wing-mounted guns, you'll often hit the target at convergence with the bullets still on their way "up" through the LoS.  With some settings you'll hit the target while the bullet is at the top of its arch.

You'll only get the "up through the LoS and back down to the target" effect shown in the rifle diagram if you shoot very far (600-800yds+).  Even then, it'll be very difficult to get hits on those shots (with that type of "intuitive" trajectory) unless you also have your convergence set within a certain span (approx 1/2 the distance to the target).

Note-  This is with wing-mounted guns!  Nose-mounts have a much more "intuitive" trajectory (like the rifle diagram illustrates).

I posted a gob-full of screen shots to depict this, but cannot find the post for the life of me...  Still looking...

[The Fugitive]

hows this one?

[SmokinLoon]

The only place multiple calibers impact differently is anywhere other than the point of convergence.  The 190A-8 literally is firing a shotgun group of projectiles unless at the point of convergence.  The 13mm and 20mm are rather close, but not perfect.  The 30mm's drop like a bowling ball.

There is something to be said for the 6/.50's or quad 20mm's.   

[mtnman]

hows this one?

(Image removed from quote.)

Same problem Fugi!

With a convergence set to 400m target at 200, the bullet will be low, and will not have come up through the LoS yet.

Really, it is kind of confusing, and no wonder that the average Hit% in AH is less than 3%.  Gunnery isn't all that intuitive, and doesn't mirror what we learn with our shoulder-fired weapons.

With a 400yd convergence, you'd need to aim slightly high at 200 yards, and possibly even slightly low to hit at 600 (probably not though, I'd have to look back at my screen shots.  I think with a 400yd convergence the bullets don't come up through the LoS much, if at all).  Opposite of what you'd expect.  And again, this is just the vertical component, and doesn't take into account the L/R crossing component.

I did most of my testing with convergence settings of 150, 300, 450, and 600yds, and consider a setting of 300 to be optimum.

[clerick]

Just fly a 38 and be done with it 

[mtnman]

Just fly a 38 and be done with it 

Lol, yup!  Anything with nose-mounts is easier, more intuitive, and the effects of trajectory are minimized.  There's also no L/R crossing aspect to toss in, which makes things even worse, particularly if you fire while your wings are banked.

Even with the ill-spoken-of 109-type cannon rounds there are few surprises when it comes to aiming.  The thing that makes those tough is the time between rounds and the low velocity, which make it tough to hit anything with a perceived motion (crossing shots, etc).

[mtnman]

Yup, the difference is that with the "rifle" diagram, the bullet comes up through the LoS before it gets to the target, and hits the target on it's way back "down".

With wing-mounted guns, you'll often hit the target at convergence with the bullets still on their way "up" through the LoS.  With some settings you'll hit the target while the bullet is at the top of its arch.

You'll only get the "up through the LoS and back down to the target" effect shown in the rifle diagram if you shoot very far (600-800yds+).  Even then, it'll be very difficult to get hits on those shots (with that type of "intuitive" trajectory) unless you also have your convergence set within a certain span (approx 1/2 the distance to the target).

Note-  This is with wing-mounted guns!  Nose-mounts have a much more "intuitive" trajectory (like the rifle diagram illustrates).

I posted a gob-full of screen shots to depict this, but cannot find the post for the life of me...  Still looking...

Aha!  Found it....

The last few posts of this thread are full of screen shots showing how convergence settings actually effect the trajectory at various ranges.  At the end I even super-imposed life-size images over the targets to show where the bullets would hit or miss, to give better perspective.

http://bbs.hitechcreations.com/smf/index.php/topic,291146.0.html

[Karnak]

hows this one?

(Image removed from quote.)

The problem is that if the firing point is ~5' below the gunsight the upward arc would have to be extreme in order for the bullets to have come down to the gunsight's level by 400 yards.  Even if it were physically possible to elevate the guns that much, which I doubt, the bullets would likely be tens or hundreds of yards above the gunsight at the peak of their arc.  There just isn't enough drop in 400 yards otherwise.