Calculating Lead in Mils

[potsNpans]

Too bad Off line missions is not working, you could just send a drone out and scale sight on it.

[Fatboy26]

I was going to say about what Mtnman said about ballistics.  There are way too many variables to even accurately guesstimate velocity loss and bullet drop at certain distances in game.  But if it helps, modern API M8 round for the M2HB have a muzzle velocity of approximately 2810 fps.  Historical data puts the velocity loss at approximately 29% at 600m.  I'm not sure what factors are used in calculating the velocity loss, because a lot of different things can make the numbers change.  I believe that the British .50 BMG used a slightly different ammunition with a higher chamber pressure  and velocity.  Are the different 12.7/13mm modeled differently ballistically or is it the same model for all of them in game?

[Ghosth]

Best bet on bullet speed is going to be a reloading book.

Although it might vary somewhat from gun to gun, by far the biggest variables are bullet weight, shape, and powder load.

Those for WWII .50 ammo should not be hard to find.

[Pyro]

Here you go.

[Ghosth]

Pyro you are the man sir!  <S>

[Baumer]

Thank you Pyro, it's much appreciated.

[Saxman]

Ok, if I'm reading the chart right, we want to use the line for the 36" barrel, which yields approximate bullet velocities of:

Range (YDS)	Velocity (FPS)	Average Velocity (FPS)
Muzzle	2850	-
200	2600	2725
400	2350	2600
600	2100	2475
800	1875	2355
1000	1675	2241

[Pyro]

You read the velocity right but I don't know what your average velocity column is or how you came up with that.  The graph is two graphs in one.  One graphs out the relation between distance and velocity for the aircraft and GV versions of the M2 .50.  You read that part right.  The next piece of the graph shows the relationship between striking velocity and armor penetration at various degrees of obliquity.  Look horizontally along your velocity line until it intersects the strike angle you want to look up.  Go straight down along the the vertical axis of the intersection point between the striking velocity and the degrees of obliquity that you're looking up and it will take you to the Penetration - Inches scale showing you how much armor penetration you can get at that velocity and that angle.

Example:  I want to know how much armor the .50 on my M8 will penetrate at 100 yards.  First find the point where the line for the 45" M2 intersects the 100 yard scale at the bottom of the graph.  Look at the velocity scale and on the left and we have a striking velocity of about 2800 f/s.  Now following the 2800 f/s line horizontally out to the obliquity angle you want to look up.  In this case we'll look at 0 degrees which would be a straight on shot.  At the point that the 2800 f/s line intersects the 0 degree obliquity curve (which is about where that curve starts), go straight down from that point and see where that ends up on the Penetration scale.  In this case it would be about 1.06".  Multiply by 25.4 and you end up with 27mm of penetration by an GV .50 at 100 yards with no obliquity.  With 60 degrees of obliquity I would get a whopping .2" or 5mm of penetration at the same range according to the graph.

[Saxman]

I calculated the average velocity under the assumption that each point on the graph where the range and velocity intersect the curve is the velocity at which the round is traveling at THAT particular range. However because the round isn't traveling at that particular velocity over the ENTIRETY of its flight, the indicated velocity would therefore not be accurate for the lead calculations (which calls for the average velocity of the round over the entirety of its flight).

For example:

I have my guns set to a convergence of 200yds, and this is the range at which I typically fire. At 200yds the round is traveling 2600fps, however this is its approximate velocity AT 200yds, and does not account for the velocity of the round as it leaves the muzzle and for every foot it travels between the moment it's fired and the moment the round reaches this range. If I were to attempt to calculate my lead based on the speed of the round AT 200yds my rounds would be falling short. So I used those two known data points--velocity at the muzzle and velocity at 200yds--to average the bullet speed over the entirety of its flight, ( (2850 + 2600) / 2 ) which is what the lead calculations call for.

[mtnman]

Can you figure out an average velocity if you don't know how long it takes the round to get to a given point?  You need to know the time of flight to figure that out accurately.

Doing the math as you have gives a possible answer, but it relies on the round slowing at a constant rate, right?  Does the round decelerate at a constant rate?

I'd expect the round to hold velocity briefly, then decelerate at an increasing rate, before finally decelerating at a reduced rate.  Once it reached a certain point (falling nearly vertically), I'd expect it to not decelerate any more at all until it hit the ground.

I'd also expect that if you knew the time of flight to different yardages, the actual velocity at those yardages wouldn't matter, since all you're trying to do at this point is hit something, rather than figure out how much damage the round does when it gets there.

[Saxman]

This is really the best I could do to figure it without having access to or knowing how to accurately test for time of flight data (considering you're getting into 10ths of a second or less I don't have the tools to try to test this myself in the game). Perfect? No, but it's what I have to work with so far, and a little bit more accurate than going strictly by actual round velocity at Range X.

I've put together a quick Excel spreadsheet that automates much of the calculation, so it's really just a matter of getting more accurate average velocity data to plug into the formulas if someone can provide it.

[mtnman]

This is really the best I could do to figure it without having access to or knowing how to accurately test for time of flight data (considering you're getting into 10ths of a second or less I don't have the tools to try to test this myself in the game). Perfect? No, but it's what I have to work with so far, and a little bit more accurate than going strictly by actual round velocity at Range X.

I've put together a quick Excel spreadsheet that automates much of the calculation, so it's really just a matter of getting more accurate average velocity data to plug into the formulas if someone can provide it.

Yea, it's probably close enough anyway.

[mtnman]

This is really the best I could do to figure it without having access to or knowing how to accurately test for time of flight data (considering you're getting into 10ths of a second or less I don't have the tools to try to test this myself in the game). Perfect? No, but it's what I have to work with so far, and a little bit more accurate than going strictly by actual round velocity at Range X.

I've put together a quick Excel spreadsheet that automates much of the calculation, so it's really just a matter of getting more accurate average velocity data to plug into the formulas if someone can provide it.

Yea, it's probably close enough anyway.

[Pyro]

Sorry, my brain got tripped up and I was thinking you were reading too far into the chart.

[Easyscor]

If I'm reading the graph right, you used the MV for the 36" barrel, but the in-flight velocities for the 45" barrel. Am I reading it wrong too?