Mg-131 13mm velocity correct?

[Mike_CK]

Ok…I’m not saying the velocity for the 13mm is far too low. I’m ASKING if anyone else believes it is b/c it seems to be to me.

so, I did an experiment. I put my aircraft about 200ft agl (220ft above sea level) looking down a runway. I placed a large building exactly 2600ft/800meters from my aircraft. The moment I start, I hit active pause (my aircraft shows 200km/h speed but for our distances, that is insignificant)

I started with the Spitfire and fired at the building. 10 tests and Both the .303s and 20mm hit the building in 1 second (give or take a .10second depending on human stopwatch error….but generally, 1 second).  That translates to a velocity of about 2500f/s or 750m/s. That matches the listed velocity of about 2400fps (740m/s)

I then tried the .50 cal on the P-47 and it was a bit less than a second. Not TOO much faster than the .303 and 20mm but seems to be Around 3,000f/s or 900m/s. Again…matches the published velocity of 870m/s. Or is close

Finally,  I put in the Bf-109 and tried the  MG-131 13mm. From the data I can find, this round has a published muzzle velocity of 2500f/s or 750m/s.….the rounds consistently took 1.5 seconds to travel that 800m and hit (again..10 tests).That translates into about 1750f/s or 530m/s.

Regardless Of how precise the time keeping is, it seems clear that the 13mm has significantly lower velocity than the Spitfires .303 even though both have the same published muzzle velocities of 2400-2500f/s (740-750m/s)

thoughts? 

(edit: I understand “muzzle velocity means just that: velocity at the muzzle. But we are talking 800meters. I don’t think a 750m/s round is losing so much velocity over 800meters that it averages  530m/s)

 

Edited May 4, 2023 by Mike_CK

[Slice313]

this is very concerning... @BIGNEWY Can you take a look? I just tested this in a server with a friend (Spitfire vs 109) and the Spitfire rounds hits considerably sooner than the 109s. They should be almost the same...

Edited May 4, 2023 by Slice313

[BIGNEWY]

please include a short track replay example on Caucasus terrain and any evidence you may have to support the claim, we will take a look 

thank you

[BIGNEWY]

We have had a quick look and all seems ok. 

Please note it is 13x64 shells we are using. 

The low power of the ammunition, combined with the large mass of the projectile, gave a low initial velocity, which ultimately had a strong effect on the ballistic characteristics of the weapon. The not very successful shape of the projectile contributed to the poor external ballistics of the weapon. All this led to the fact that after exiting the barrel, the projectile quickly lost speed. 

[Hobel]

vor 10 Stunden schrieb Mike_CK:

Ok…I’m not saying the velocity for the 13mm is far too low. I’m ASKING if anyone else believes it is b/c it seems to be to me.

so, I did an experiment. I put my aircraft about 200ft agl (220ft above sea level) looking down a runway. I placed a large building exactly 2600ft/800meters from my aircraft. The moment I start, I hit active pause (my aircraft shows 200km/h speed but for our distances, that is insignificant)

I started with the Spitfire and fired at the building. 10 tests and Both the .303s and 20mm hit the building in 1 second (give or take a .10second depending on human stopwatch error….but generally, 1 second).  That translates to a velocity of about 2500f/s or 750m/s. That matches the listed velocity of about 2400fps (740m/s)

I then tried the .50 cal on the P-47 and it was a bit less than a second. Not TOO much faster than the .303 and 20mm but seems to be Around 3,000f/s or 900m/s. Again…matches the published velocity of 870m/s. Or is close

Finally,  I put in the Bf-109 and tried the  MG-131 13mm. From the data I can find, this round has a published muzzle velocity of 2500f/s or 750m/s.….the rounds consistently took 1.5 seconds to travel that 800m and hit (again..10 tests).That translates into about 1750f/s or 530m/s.

Regardless Of how precise the time keeping is, it seems clear that the 13mm has significantly lower velocity than the Spitfires .303 even though both have the same published muzzle velocities of 2400-2500f/s (740-750m/s)

thoughts? 

(edit: I understand “muzzle velocity means just that: velocity at the muzzle. But we are talking 800meters. I don’t think a 750m/s round is losing so much velocity over 800meters that it averages  530m/s)

hm interesting test.

one more note, if you press the active pause and the aircraft was flying at let's say 600km/h from that point on, it should be added to that, at least it is with many other weapons, if it is the same here I can't say for sure.

that means there should be a difference between an active pause between say 100km/h or 600km/h.

[Mike_CK]

Yeah…I was flying at 200kmh so don’t think it affected it

but Bignewy, thank you for taking a look. As I said, I don’t know a lot about this stuff so I was curious as to why I observed what I did. You say it’s accurate so it’s accrurate.

[303_Kermit]

13 hours ago, BIGNEWY said:

We have had a quick look and all seems ok. 

Please note it is 13x64 shells we are using. 

The low power of the ammunition, combined with the large mass of the projectile, gave a low initial velocity, which ultimately had a strong effect on the ballistic characteristics of the weapon. The not very successful shape of the projectile contributed to the poor external ballistics of the weapon. All this led to the fact that after exiting the barrel, the projectile quickly lost speed. 

After wikipedia:
https://en.wikipedia.org/wiki/MG_131_machine_gun
 

Muzzle Velocity of 13x64mm:
From 13 mm Panzerbrandgranatpatrone (API) - 710m/s (projectile 38g) up to 770m/s for 13 mm Brandgranatpatrone El. ohne Zerleger (I) (projectile 34g).
to see the difference comparison will be justified:
50 BMG (also after wikipedia):
From 928m/s (Projectile 42g ), up to 882m/s (projectile 52g)
12,7x109mm (also after wikipedia)
From 920m/s (Projectile 44g ), up to 820-860m/s (projectile 48g)
... I would rather say that german ammunition (compared by muzzle velocity and projectile) is rather lighter than their USA or UDSSR counterparts.

Finally .303 British:
From 844 m/s (10 g projectile) up to 783 m/s (12 g projectile) - similar muzzle velocity, but much much lighter projectile shall loose speed rapidly compared to German ammunition.

PS: A2G ammo belt of MG131 seem to be quite ineffective. Why is that? LF MkIX (AI )set to "No Reaction to threat" needs almost whole ammo of 2x MG131 (A2G ammo belt) (I used Bf-109) to be destroyed.

Edited May 4, 2023 by 303_Kermit

[razo+r]

On 5/4/2023 at 6:03 PM, Mike_CK said:

Yeah…I was flying at 200kmh so don’t think it affected it

but Bignewy, thank you for taking a look. As I said, I don’t know a lot about this stuff so I was curious as to why I observed what I did. You say it’s accurate so it’s accrurate.

In case you want some values:

The muzzle velocity seems to be set correctly (v0).

However, if you compare the drag coefficient, you'll see the 13mm is draggier than for example the .50 or .303.

MG131

.50

.303

I personally have no idea if that is entirely accurate, but it would explain your observations.

Edited May 7, 2023 by razo+r

[Hobel]

vor 4 Minuten schrieb razo+r:

However, if you compare the drag coefficient, you'll see the 13mm is draggier than for example the .50 or .303.

Hm.  Wasn't there once a topic about the 50cal also having too much drag or something? I can't remember exactly and I can't find the topic right now. 

[razo+r]

1 minute ago, Hobel said:

Hm.  Wasn't there once a topic about the 50cal also having too much drag or something? I can't remember exactly and I can't find the topic right now. 

 

[Hobel]

vor 1 Minute schrieb razo+r:

 

nah, I don't think it was that one, there was another one. But thank you.

[Skewgear]

3 hours ago, Hobel said:

Hm.  Wasn't there once a topic about the 50cal also having too much drag or something? I can't remember exactly and I can't find the topic right now. 

I think I remember the one you mean but i can't find it either now. Someone with a detailed grasp of external ballistics and a bit too much time on his hands wrote a dissertation on here about why the 50-cal values were wrong.

I wish I could find it because there were a couple of insights worth having from it, albeit on the 50-cal rather than the 109's armament.

The only way to derive the values for sure is to fire original projectiles and measure them using a Doppler radar, and I don't think that's happening any time soon.

[MrExplosion]

You can check page 8 and following to get detailed measurements of velocity / kinetic energy at different distances and compare that to the in game results. 

Handbuch der Flugzeug Bordwaffenmunition 1936-1945.pdf

[Hobel]

vor 3 Stunden schrieb MrExplosion:

You can check page 8 and following to get detailed measurements of velocity / kinetic energy at different distances and compare that to the in game results. 

Handbuch der Flugzeug Bordwaffenmunition 1936-1945.pdf 7.31 MB · 0 Downloads

Thx!

 

So DCS is spot on

 

 

Edited May 7, 2023 by Hobel

[MrExplosion]

3 hours ago, Hobel said:

Thx!

 

So DCS is spot on

 

 

 

Yes, I just wonder if damage dealt is realistically modelled. Germans kept that ammo throughout the war, so if ballistics was bad they probably had other reasons to use it.

Edited May 7, 2023 by MrExplosion

[Magic Zach]

Probably just because it was a standardized aircraft weapon, and by the time anyone might have realized it could be inadequate it was too late to be worth making a new generation of armament while all your manufacturing facilities are being targeted by bomber raids.

ime the 13mm is adequate for me though in DCS.  iirc it has more explosive filler and the fact it even has any makes up a bit for lower velocity

9 hours ago, Skewgear said:

I think I remember the one you mean but i can't find it either now. Someone with a detailed grasp of external ballistics and a bit too much time on his hands wrote a dissertation on here about why the 50-cal values were wrong.

I wish I could find it because there were a couple of insights worth having from it, albeit on the 50-cal rather than the 109's armament.

The only way to derive the values for sure is to fire original projectiles and measure them using a Doppler radar, and I don't think that's happening any time soon.

it's in the research channel of the 4YA PO discord, by Yak Panther.  He's the go-to to ask about FM and ballistic research in the ww2 flight Sim playerbase