MK 108 Shells too slow

[razo+r]

So i found it...

 

A lot of sources say, the muzzle velocity was from about 505/525 to 540 m/s, but in DCS, it's slower:

 

  [1] = 3 cm M-Gesch. Patr. 108 m. Zerl Ausf. A


     v0              = 500.0,

 

This here is about 20 m/s too slow, unless i'm missing some sources that say, they're slower than 525 m/s

 

  [2] = 3 cm M-Gesch. Patr. L.Spur 108 m. Zerl


     v0              = 500.0,

 

This here is the same as above

 

 

  [3] = 3 cm Brgr. Patr. 108 m. Zerl


     v0              = 485.0,

 

This one is about at least 20-40 m/s too slow...

 

I know it wouldn't make too much of a difference, but 20 m/s isn't nothing...

 

Maybe it would be worth it looking at that and see if that's really wrong

[Schmidtfire]

Great find! That higher muzzle velocity might actually help a bit with aiming as the shells wont drop as quickly.

[9.JG27 DavidRed]

if you are correct, then nice find...

what i would also want to know from the devs is, why the Mk108 is pointing downwards...i was always thinking that the cannon was pointing straight through the engine block and the spinner, but in dcs its hanging downwards according to the .lua file.

[rel4y]

The ballistics are correct for the modelled round. It is simply mislabled, actually its called Minen-Brandgranatpatrone and its functionally a mix of the Brandgranatpatrone and Minengranatpatrone. Truth is, the Brandgranatpatrone has not been modeled at all as of yet.

 

See here: https://forums.eagle.ru/showthread.php?t=170408

Edited January 10, 2017 by rel4y

[gavagai]

Great find! That higher muzzle velocity might actually help a bit with aiming as the shells wont drop as quickly.

 

The shells will drop at the same rate, but they will go farther while they drop.;)

[amazingme]

I checked the documentation and it seems that our 1945 Bf 109 uses 1940 ammunition. This should be re-checked by ED and update the sim accordingly.

[rel4y]

What do you mean? The top mentioned round was introduced in 1944, so what exactly is 1940 about the DCS ammo?

[amazingme]

The rounds were much earlier developed.. starting since '37s. The muzzle velocity was increased due to using of the newly discovered chemicals such as 'hexogen' or 'cyclonite'.

[rel4y]

So you say the germans should have used Hexogen and Cyclonite (which are the same thing by the way) in the shells as propellant.. lol :D

 

May I ask you where you got your knowledge about explosives from? Cause that is one of the worst ideas I have ever heard.

 

Hexogen was used as an explosive compound in artillery shells. The 30mm rounds were filled with PETN or Nitropenta as it is called in Germany and most often Tetryl as a charge booster.

[amazingme]

First of all, 'OR' denotes interchangeable terms OR synonyms.

Second, I'm not a chemist but I know how to read English, and I found out that hexagen was discovered by a german chemist in 1898 and later patented under Patent Nr. 104280.

Third, this chemical was also used for FLAK shells which, as data show, were capable of 1000m/s at the same or larger calibre.

You can check this https://books.google.ro/books?id=bmREBgAAQBAJ&pg=PA24&lpg=PA24&dq=hexogen+rounds+muzzle+velocity&source=bl&ots=YW4Dhvctk5&sig=pPqJT9rkApPGQWVqSKmBsyXBo50&hl=en&sa=X&ved=0ahUKEwinwZD0z7fRAhXI1IMKHR29DbMQ6AEIKTAC#v=onepage&q=hexogen%20rounds%20muzzle%20velocity&f=false

We can also calculate based on the chemical reaction, mass and the gas pressure velocity /cm^2 what muzzle velocity a particular shell can reach. I let you do the math.. it's simple.

[amazingme]

So i found it...

 

...

 

v0 = 485.0,[/code]This one is about at least 20-40 m/s too slow...

 

I know it wouldn't make too much of a difference, but 20 m/s isn't nothing...

 

Maybe it would be worth it looking at that and see if that's really wrong

 

The kinetic energy is exponentially proportional to the speed, so 20 m/s or even 40m/s would have a huge impact on the shell trajectory.

Edited January 10, 2017 by amazingme

[rel4y]

lol :D your funny. I like you.

[Schmidtfire]

Hmm... Maybe we should ask Sith or someone else to post a proper bug report about this, if we have good documentation on it? Slower muzzle velocity+downwards pointed barrel doesn't sound like a good combination. (And might explain why the gunsight is nearly useless for the mk108 )

[amazingme]

hmm

 

lol :D your funny. I like you.

-> this is called 'ad hominem'.

[rel4y]

Well sorry.. you come to the party with this:

 

I checked the documentation and it seems that our 1945 Bf 109 uses 1940 ammunition. This should be re-checked by ED and update the sim accordingly.

 

The rounds were much earlier developed.. starting since '37s. The muzzle velocity was increased due to using of the newly discovered chemicals such as 'hexogen' or 'cyclonite'.

 

First of all the rounds for MK101, 103 and 108 were all developed in the 40s. The one I mentioned earlier as late as 44. In the late 30s was the first time that cannons were introduced at all for german aircraft and these were the 20mms based on Oerlikon designs. Next you are saying they used RDX as a propellant.. There is a nice anecdote where this was actually done. In Vietnam the US forces dropped "modified" 7.62x39mm for the AKs of the North Vietnamese, when actually firing one of these doctored shells the whole rifle blew up in the face of the poor guy and either blew his head of or wounded him badly. So hopefully now you have realized that the type of explosive of the filler has no relevance to v0 of the projectile.

 

Third, this chemical was also used for FLAK shells which, as data show, were capable of 1000m/s at the same or larger calibre. ... We can also calculate based on the chemical reaction, mass and the gas pressure velocity /cm^2 what muzzle velocity a particular shell can reach. I let you do the math.. it's simple

 

So a FLAK shell is not from FLAK artillery? That sounds like a sassy comment of a 14 year old. That whole paragraph is ridiculous.. No you can certainly not calculate v0 based on the chemical reaction, mass and gas pressure. Theres barrel length, there is barrel twist dependent on target v0, there is cartridge neck angle, there is powder burn rate, powder burn efficiency. What the heck do you even mean by calculating based on chemical reaction? I had 3 years of chemistry and 5 years of physics in university, so you can stop trying to sound smart its not gonna work.

 

The kinetic energy of a projectile is useless for trajectory characterization. You can derive it at any time point of the function, but it tells you just about zero about the trajectory. The ballistic coefficiant is important to look at, as a projectile with higher v0 will loose its kinetic energy initially at a higher rate than a slower one. Drag effects are exponential, so its not a linear dependancy. I can derive the BC of the MK108 projectile tomorrow as I have all the ballistic tables at home for these rounds. Then I can calculate the difference in drop, but I can predict today that its gonna be sub MOA. And sub MOA means that the gun dispersion is larger than the difference in drop, which makes this whole discussion senseless..

 

You cant simply look at this with 7th grade physics and claim this:

I checked the documentation and it seems that our 1945 Bf 109 uses 1940 ammunition. This should be re-checked by ED and update the sim accordingly.

 

I dont know what and where you checked, but this is an insult to all the great work ED has done..

[javelina1]

OP, nice find. thanks! Curious to see what develops.

[Hammer1-1]

Well sorry.. you come to the party with this:

 

 

 

 

 

First of all the rounds for MK101, 103 and 108 were all developed in the 40s. The one I mentioned earlier as late as 44. In the late 30s was the first time that cannons were introduced at all for german aircraft and these were the 20mms based on Oerlikon designs. Next you are saying they used RDX as a propellant.. There is a nice anecdote where this was actually done. In Vietnam the US forces dropped "modified" 7.62x39mm for the AKs of the North Vietnamese, when actually firing one of these doctored shells the whole rifle blew up in the face of the poor guy and either blew his head of or wounded him badly. So hopefully now you have realized that the type of explosive of the filler has no relevance to v0 of the projectile.

 

 

 

So a FLAK shell is not from FLAK artillery? That sounds like a sassy comment of a 14 year old. That whole paragraph is ridiculous.. No you can certainly not calculate v0 based on the chemical reaction, mass and gas pressure. Theres barrel length, there is barrel twist dependent on target v0, there is cartridge neck angle, there is powder burn rate, powder burn efficiency. What the heck do you even mean by calculating based on chemical reaction? I had 3 years of chemistry and 5 years of physics in university, so you can stop trying to sound smart its not gonna work.

 

The kinetic energy of a projectile is useless for trajectory characterization. You can derive it at any time point of the function, but it tells you just about zero about the trajectory. The ballistic coefficiant is important to look at, as a projectile with higher v0 will loose its kinetic energy initially at a higher rate than a slower one. Drag effects are exponential, so its not a linear dependancy. I can derive the BC of the MK108 projectile tomorrow as I have all the ballistic tables at home for these rounds. Then I can calculate the difference in drop, but I can predict today that its gonna be sub MOA. And sub MOA means that the gun dispersion is larger than the difference in drop, which makes this whole discussion senseless..

 

You cant simply look at this with 7th grade physics and claim this:

 

I dont know what and where you checked, but this is an insult to all the great work ED has done..

I think what he is trying to explain is that the powder mix would propel the projectile at a higher velocity due to a higher decay rate with the material. If they can shoot flak shells, it wouldnt be too hard to shoot smaller ammunition with it. Without sounding like an idiot myself, I think he is referring to a different propellant mix that has a little bit more oompf out of the charge. Maybe the specific round has more grain in the brass. The rifle twists in the barrel, the length of the barrel, and gas mechanism wouldnt really play an obvious role in kinetic energy when shooting different rounds out of the same barrel. What about the projectile itself? Does it have a tendancy to tumble? Does it have less mass?

[rel4y]

Nooo you cant use RDX as propellant, too high expansion and burn rate. That's a secure way to get everyone involved killed and the gun destroyed. Noone would do that, that's completely stupid. Peak pressure would bust any chamber. That one is called a bomb.

 

These explosives were used as a explosive charge within the round, but as propellant you always have to use slow burning powdered charges. With more powder in the same cartidge you lose burn efficiency if you are over the optimal fill percentage. That's were the neck angle comes into play as well. Rifle twist is adjusted at an optimal target v0, if this is exceeded the round well slip over the twist and the projectile becomes unstable. A higher cartridge propellant load must not mean higher peak or effective chamber pressures and higher pressure peak rates don't automatically mean a better trajectory. Like I said, this can't be done with 7th grade physics.

 

Now to the historical view of this. The Germans used throughout the war the same propellant in their cartridges. There were higher v0 8x57mm cartridges produced for the Luftwaffe since 1940, because the cartridge allowed for that. And this was certainly not done by adding RDX to the propellant. The MK108 was a modified and down sized MK101/103 cartridge which limited it's usefulness from the very inception. The case was basically filled to the brim with propellant already, but it was small and comparatively light.

 

The MK108 has a complex design by itself. Let me put it in simple words. The breech is non locking and the cartridge is fired before it is completely inserted into the barrel. This is practical as much of the recoil is absorbed by mass inertia of the heavy breech, but also means RPM is directly tied to effective pressure and recoil of the cartridge. The barrel had to be kept a stump so the pressure rates would not exceed cartridge and gun limits. Late in the war there were experiments done to increase RPM of the MK108, this was actually done by strengthening the buffer springs and decreasing breech weight for lower breech inertia and faster cycle rates. They reached theoretical RPMs of up to 1200 but the bad quality stamped sheet metal and she'll casing could not support it. Higher v0 was never really an option, as that would have needed a longer barrel to allow for the propellant load to actually be converted into velocity. But the resulting peak pressure rates would have destroyed the gun.

 

I hope I kept it simple enough to be understandable.

 

PS: like I said earlier, the shell ballistics are correct, but the shell is mislabeled. It is actually the heavier (370g) M-Brandgranatpatrone and not the normal Brandgranatpatrone (330g), which explains the lower v0.

Edited January 11, 2017 by rel4y

[amazingme]

Well sorry.. you come to the party with this:

 

 

 

 

 

First of all the rounds for MK101, 103 and 108 were all developed in the 40s. The one I mentioned earlier as late as 44. In the late 30s was the first time that cannons were introduced at all for german aircraft and these were the 20mms based on Oerlikon designs. Next you are saying they used RDX as a propellant.. There is a nice anecdote where this was actually done. In Vietnam the US forces dropped "modified" 7.62x39mm for the AKs of the North Vietnamese, when actually firing one of these doctored shells the whole rifle blew up in the face of the poor guy and either blew his head of or wounded him badly. So hopefully now you have realized that the type of explosive of the filler has no relevance to v0 of the projectile.

 

 

 

So a FLAK shell is not from FLAK artillery? That sounds like a sassy comment of a 14 year old. That whole paragraph is ridiculous.. No you can certainly not calculate v0 based on the chemical reaction, mass and gas pressure. Theres barrel length, there is barrel twist dependent on target v0, there is cartridge neck angle, there is powder burn rate, powder burn efficiency. What the heck do you even mean by calculating based on chemical reaction? I had 3 years of chemistry and 5 years of physics in university, so you can stop trying to sound smart its not gonna work.

 

The kinetic energy of a projectile is useless for trajectory characterization. You can derive it at any time point of the function, but it tells you just about zero about the trajectory. The ballistic coefficiant is important to look at, as a projectile with higher v0 will loose its kinetic energy initially at a higher rate than a slower one. Drag effects are exponential, so its not a linear dependancy. I can derive the BC of the MK108 projectile tomorrow as I have all the ballistic tables at home for these rounds. Then I can calculate the difference in drop, but I can predict today that its gonna be sub MOA. And sub MOA means that the gun dispersion is larger than the difference in drop, which makes this whole discussion senseless..

 

You cant simply look at this with 7th grade physics and claim this:

 

I dont know what and where you checked, but this is an insult to all the great work ED has done..

 

Unfortunately I can't comment what you're saying because, and I quote:

'The ballistic coefficiant is important to look at, as a projectile with higher v0 will loose its kinetic energy initially at a higher rate than a slower one'.. water is wet..

'The kinetic energy of a projectile is useless for trajectory characterization.' .. pure rubbish

'In Vietnam the US forces dropped "modified" 7.62x39mm for the AKs of the North Vietnamese'.. german engineers are not vietnamese soldiers, so I would pay a bit more respect to engineers

'So a FLAK shell is not from FLAK artillery?'.. you don't understand English language.

 

My conclusions:

1. I really doubt you have the studies you mentioned

1'. Your arguments are NOT on point

1''. I will completely ignore you from now on.

[9.JG27 DavidRed]

rel4y,...didnt you say, that the masses were close but slightly off in dcs, in your other thread?

 

what i still would like to get an answer on though is, why our 109 has the mk108 pointing downwards?

 

that would only be possible if the spinner had a cone shaped opening, and the whole engine placed in a hanging attitude...but i dont see that in any drawings...

 

in E:\DCS World\CoreMods\WWII Units\Bf-109K-4 we have the Bf-109K-4.lua, were in line 296 it says:

 

elevation_initial = -0.069,

 

so the barrel is pointing downwards it seems. is that a bug?

[rel4y]

The engine of the 109 was angled slightly downwards in real life as well. The barrel should be in line with the holllow hub. So might be just that. I dont know what the reference grid is though. I checked the trajectory some time ago and it is pretty much on the point. Only the belt pieces are slightly too heavy afaik.

 

 

My conclusions:

1. I really doubt you have the studies you mentioned

1'. Your arguments are NOT on point

1''. I will completely ignore you from now on.

 

As long as you spare me your pseude science, Im fine with whatever you think.

Edited January 11, 2017 by rel4y

[amazingme]

Someone is waving some tables and thinks he does science...

Mkay.. let's do some science..

 

Ballistic coefficients:

 

• G1 or Ingalls (flatbase with 2 caliber (blunt) nose ogive - by far the most popular)[87]
  
• G2 (Aberdeen J projectile)
  
• G5 (short 7.5° boat-tail, 6.19 calibers long tangent ogive)
  
• G6 (flatbase, 6 calibers long secant ogive)
  
• G7 (long 7.5° boat-tail, 10 calibers tangent ogive, preferred by some manufacturers for very-low-drag bullets[88])
  
• G8 (flatbase, 10 calibers long secant ogive)
  
• GL (blunt lead nose)
  

Which ballistic coefficient ED is using for Mk 108 ammunition (there are two types though, as seen in the .lua file)?

The easiest method is this (as I stated in my previous comments):

 

Kinetic Energy (KE) = 1/2 MV2

 

 

As I stated before, the shell trajectory depends on the initial velocity:

 

 

 

 

https://en.wikipedia.org/wiki/Trajectory_of_a_projectile

http://www.cleverinsite.com/ballistics/calcs.asp#rangelnk

http://library.med.utah.edu/WebPath/TUTORIAL/GUNS/GUNBLST.html

 

 

http://www.hornady.com/ballistics-resource/ballistics-calculator

 

Using 485m/s

 

Range (meters) Velocity (mps) Energy (joules) Trajectory (cm) Come UP in MOA Come UP in Mils Wind Drift (cm) Wind Drift in MOA Wind Drift in Mils Muzzle4852858-5000005047427260000.80.60.21004622599-62.10.62.710.31504512476-23.65.41.65.91.50.42004402356-53.69.22.710.520.62504292241-95.813.23.816.62.50.73004192130-152.417.55.124.130.9

Using 540 m/s:

 

Range (meters) Velocity (mps) Energy (joules) Trajectory (cm) Come UP in MOA Come UP in Mils Wind Drift (cm) Wind Drift in MOA Wind Drift in Mils Muzzle5403543-5000005052833870000.70.50.21005163237-3.81.30.42.30.90.31505043092-173.91.15.11.30.42004932951-40.16.9291.70.52504812816-72.9102.914.12.10.63004702686-117.113.43.920.42.60.7

Any questions?

[amazingme]

One more thing:

"In physics, the ballistic trajectory of a projectile is the path that a thrown or launched projectile or missile without propulsion will take under the action of gravity, neglecting all other forces, such as friction from aerodynamic drag."

[razo+r]

yep, now some questions are coming:

 

1. rel4y, in your doc, it's stated 500m/s, do we have that ammo in DCS, from where is that doc and how much can you trust that source?

 

2. amazingme, thanks a lot for your calculation, i'm also intrested in the change of the range, but so many numbers with . or -, could you highlight or show me the distance or the difference of the distance?

Thanks

[rel4y]

Oh my... "in physics", yes cause these are the simplified formulas for school kids. If you actually wanna get close to real world results then maybe you should quote the next paragraph from wikipedia or wherever you got that from.. and sure trajectory depends on v0, I have said that more than once. Just kinetic E doesnt give you jack info about it like you started off.

 

Just let it be ok?! Im done.

 

The ballistic tables are from the official Rechlin documents and the rest is from the Luftwaffe LDv (Dienstvorschriften) of 1944. By the way the same ones Yo-Yo used with 99% safety. I have named my sources in the other thread that obviously noone bothers to read.

 

The ballistic tables are from Handbuch der Flugzeugbordwaffenmunition 1936-1945. The colored drawings are taken from LDv 4000/10. (de.scribd.com/doc/214886494/L-Dv-4000-10-Munitionsvorschrift-fur-Fliegerbordwaffen-Teil-10-1944)

Edited January 11, 2017 by rel4y