flight trajectory and "miss" calls

[dcali]

You're getting tripped up over the angular corrections vs the curvature of the trajectory. With the scope, you can make perfect angular corrections at any range - the line of sight is a straight line. So if you hit 3MOA lower than you want at any range, you dial exactly 3MOA to correct for it.

Now that your scope is pointing 3 MOA down from your first shot, you have to move the rifle up 3 MOA to hit the original target . You've now changed the angle of departure of the bullet, so the trajectory will be very slightly different - it's not a rigid rotation of the trajectory curve. So yes, there will be some error in your second shot. In practice, it's very small and ignorable. Maybe the guys who shoot at 4000 yards have to deal with it. I've never checked the math or shot anywhere near that far personally. But at 1000 it's not an issue.

Sometimes it helps to think about these issues by picturing extreme cases. Imagine a normal flat fire case, and then imagine aiming up at 88 degrees or something like that to hit the exact same impact point. Clearly, the scope adjustment in that case (88 degrees worth) has resulted in *no* impact change. If it were rigid, you'd see 88 degrees worth.

 

[Bart B.]

Most 30 caliber bullets angle of fall at 1000 yards is around 2 to 3 degrees with a 30 to 45 MOA up LOF. Elongated holes in targets will be difficult to see.

If bullets spin axis is always aligned with bore axis, how much does their BC change at extreme ranges when their spin axis is a few dozen degrees from their trajectory axis? Does ballistic software compensate for this?

Why do projectiles from large caliber military guns leave 45 to 60 degree down angled holes in earth at maximum ranges with diameters the same as projectiles' diameter? They often have point detonating fuses, not side detonating ones

Passed footballs' spin axes nose over at their trajectory peak, don't they?

 

[Bart B.]

The bullet very closely tracks the trajectory. The bullet is angled slightly down at 1000 yards.

Yes; bullet spin axes are virtually parallel to their trajectory.

 

[Bart B.]

Let's start with a hypothetically perfect scenario.

We have a perfect barrel. The outside is round and true. The bore is perfectly round and concentric to the outside diameter. The bore runs straight through the center of the barrel. The barrel is pointed perfectly at a .001" dot that is 100 yards away. There is no wind, no mirage, no heating effect of the air, the only things that will affect the flight of the bullet are the resistance of the air as the bullet flies through it and gravity. Magically gravity does not affect the barrel so it has no droop. The barrel is in an ultimate Benchrest rig so that it is perfectly aligned to the dot on the target.

The bullet fired from this barrel will miss the target because gravity will cause the bullet to drop slightly.

The bore axis changes while bullets go through it. The recoil axis is typically above the rifles center of mass, so it's axis rises during barrel time before the bullet exits.

If the rifles is held against ones shoulder when fired, the recoil axis is to one side of the center of mass holding it, The bore axis moves horizontally during barrel time.

The muzzle axis is vibrating vertically several hundred cycles per second when bullets leave. The arc of that swing is several dozen MOA. Stiffer barrels do so at higher frequencies.

Only when the bullet exits the barrel is the bore axis aligned to a point above the point of aim on target equal to bullet drop plus sight height. The bore axis may also be horizontally offset from point of aim to compensate for wind and spin drift.

This is why several people shooting the same stuff with the rifle shouldered will have a different zero on the sight. And why tuning weights on muzzle ends adjust the muzzle axis vibrating frequency to compensate for velocity spread so slower ones leave at a higher angle above LOS to compensate for their greater drop at target range.

 

[Bart B.]

The spin should keep the bullet point level. If you look at holes in a target at 1000, they are round if the gun is tuned. It the bullet is entering point down the holes would be oblong.

Been thinking about this claim.

Do you mean the bullet long axis is horizontal throughout its flight even if the bore axis was angled 45 MOA up to compensate for a 450 inch drop at 1000 yards?

Same if the bore axis was angled about 40 degrees up to hit targets several thousand yards away?

What about planes diving down at 45 degrees, do their machine gun bullets nose up so they're level in the horizontal axis?

Please explain the physics that orients bullet long axis horizontally after it leaves the barrel regardless of its LOF up or down angle. Note a bullet trajectory at 1000 yards angling down 4 degrees with its long axis horizontal will make a hole in the target about .25% larger vertically than bullet diameter, width will be bullet diameter.

 

[Northridge]

side note: I've witnessed oblong holes in paper targets that are not flat on backer board completely & with tunes that are more than stable.

Shawn Williams

 

[Bart B.]

A study of bullets' impact angle of obliquity to the target surface will show its spin axis is virtually parallel to its trajectory.

Passed football's spinning 500 to 600 rpm nose over in their trajectory just like bullets do.

 

[dcali]

If you do the math on the angle that the bullet hits the target at 1000 yards, even roughly (take the drop over the last 100 yards, for example, and work out the angle - that will be a slight under-estimate), you'll find that the angle is very small - on the order of 1-3 degrees. When you work out the impact that has on the dimensions of the hole, it's too small to detect given the nature of paper.

For example, for a 1 degree angle of impact, a .30800" bullet will make a hole that is .30804" tall. A 3 degree angle will make a hole .30842" tall. You can't see that.

When people do see them, I wonder if it's because the instantaneous yaw is relatively large at impact. Weird things happen at long range.

For further evidence that bullets' noses follow the trajectory (not exactly, but closely), if you look at a bullet shot at ELR ranges - 3-5000+ yards, they're not going fast enough to come apart on impact. You'll see that the nose is bent to the side, and not mushroomed. This bullet was an impact with a steel plate at 5000 yards. Of course this too could be caused by an instantaneous yaw, but it would have to be a very large one - borderline tumbling.

Really, though - this is settled, mature science. It's not really up for debate. If it were not true, ballisitics calculators wouldn't work, and artillery would always miss. The implications of the aerospace/defense industry being wrong about this are so huge that it's hard to actually imagine them. You have to re-write Netwon's laws or discover new forces to make bullets not track the trajectory (in our case - I'm not talking about 85 degree angles or other weird special cases).

 

[Bart B.]

If you do the math on the angle that the bullet hits the target at 1000 yards, even roughly (take the drop over the last 100 yards, for example, and work out the angle - that will be a slight under-estimate), you'll find that the angle is very small - on the order of 1-3 degrees.

Thanks for agreeing with my comments in posts #22 and #25.

I used Sierra's software to get bullet drop from 995 yards to 1005 yards. Then calculated the bullet's angle of obliquity. It works out that a 5/8ths inch drop per yard of range is almost exactly 1 degree angle of fall or trajectory.