fixed Super slow .50 caliber rounds

[BIGNEWY]

This is reported to the team and I have added the data to the report

 

thanks

[Zimmerdylan]

  So in 2016 this topic was posted in the bugs and problems section. It was hashed over, thought out, supposedly reported, and over 4 years later is still being complained about. And not addressed according to everything I see. No fix in sight. 4 years folks. 4 years.....

 This is the only reason that I never really fly the F86 ( a great plane by the way). It's nearly useless in A/G or A/A combat. 4 years.......

 Now, when someone new discovers this problem, they tell them it's reported and close the thread. Really ED????? Come on....I guess I expect too much from you guys..........

 This is why I went 2 years without buying anything. And maybe will go back to that stance. Such a disappointment that my money is being tossed away on things that will never be finished to the point of the satisfaction of those who purchased them. 

 Temp ban me, suspend me, do whatever you want. This is a very legitimate problem. Making those who are unhappy and are asking ED politely (and then maybe not so politely after years of asking) to fix the problem feel out of line for expecting to get what they paid is not acceptable.  Many of the issues that have plagued some of these modules for years end up in this old hidden dust bin. I kind of need to start seeing something more than forum promises. I think that all of us deserve that much from ED. It's our money you are getting. 

[MiG21bisFishbedL]

The length of time and absolute hoops the community has had to jump through to get a simple LUA change done has been absolutely ridiculous. Honestly, in a just world, ED would have given Curly a bonus of some kind for doing their job for them. 

 

That's assuming ED has the gumption to put in changes, an LUA change at that, instead of just ignoring it for some unspecified reason? 

This entire episode has been utterly ridiculous. It has been utterly unacceptable. Mosquito is not getting a purchase from me and the Apache is looking even more tentative as something I want to fork over cash for. 9L catches a lot of bovine by-product, but to his credit, he looks to have done right by us in this case. It might be a good idea, call me crazy, to listen to community reps such as himself as the developer. You know, guys you've appointed to moderate over these forums?

 

You can do better, ED.

Edited July 27, 2021 by MiG21bisFishbedL

[nighthawk2174]

45 minutes ago, MiG21bisFishbedL said:

The length of time and absolute hoops the community has had to jump through to get a simple LUA change done has been absolutely ridiculous. Honestly, in a just world, ED would have given Curly a bonus of some kind for doing their job for them. 

 

That's assuming ED has the gumption to put in changes, an LUA change at that, instead of just ignoring it for some unspecified reason? 

This entire episode has been utterly ridiculous. It has been utterly unacceptable. Mosquito is not getting a purchase from me and the Apache is looking even more tentative as something I want to fork over cash for. 9L catches a lot of bovine by-product, but to his credit, he's looks to have done right by us in this case. It might be a good idea, call me crazy, to listen to community reps such as himself as the developer. You know, guys you've appointed to moderate over these forums?

 

You can do better, ED.

Agreed and the amount of documents that had to be posted even just for this to once again get looked at... This fix should take only a few minutes to make and test and maybe another 10 or so to read through the documents posted.

[VampireNZ]

Yep it is a shame - but welcome to DCS really. This is how it has been , as you say, for years - with no sign of ever changing. That's why for every module I own I have a selection of mods in OvGME fixing the basic things ED can't be bothered fixing - mostly really basic LUA 1-line changes like the F-86 gun fix you mention. Is also why I won't be spending another cent on DCS for the foreseeable future either as I am tired of 'half-finished for years' modules.

Which is a shame as I live on NZ and used to work at Ardmore airfield and been in the hangar where they restore the Mosquito, seen them fly many times and was keen to purchase, but guess I am just not seeing the point anymore of spending my limited sim time flying half-finished neglected modules.

Also sick and tired of the DCS sniper-AI taking down a Hind (and other choppers) with a single 'golden BB' small arms fire. I swear the guy that programs the DCS AI must be a multiple gold medal winner in 'Blindfolded Skeet Shooting' to think you can plink a couple of snapshots of 7.62mm at a passing low-level helicopter doing 250kph and magically score a direct hit on the control system immediately rendering the machine uncontrollable (Looking at you UN Campaign remade for Hind Mission 2 I think it is)...... now I just select invulnerable in the options and enjoy the mission instead, and use 'Red Flag' techniques to know if I stuffed up and 'actually' died - or DCS magic AI at work again.

Bit of a rant I know, but meh.

[streakeagle]

It is quite a bit annoying that the gunsight hasn't been at the level of accuracy it should be at despite ED having been provided the cause and solution to the problem some time ago. But it is far from a show-stopper does not keep me from enjoying the F-86. I find the fact that the in-cockpit sound randomly cuts out and can only fixed by spawning in another F-86 to be far more annoying, yet this problem has been around quite some time as well and ED says it can't reproduce it, so they aren't going to fix it.

Edited July 24, 2021 by streakeagle

[Zimmerdylan]

  And it extends into so many areas that I get insanely frustrated with DCS and quit for months at a time. It just sucks. I recently came back to DCS some months ago after a year or so. I even purchased 2 more modules and maps. It all seems ok on the surface and it's lots of fun to just fly around, maybe shoot some stuff up (Kudos on that ED), but when you want to go in depth and use the ME or learn some advanced systems stuff, you have to hope and pray that they fixed things enough for you to do it. I went into the ME and tried to set up simple missions and unless I alter LUA after LUA, the vehicles, planes, boats, troops, tasks, wing men, and pilots act like mindless, slobbering zombies, doing whatever they like....Certainly not what I programmed them to to in the ME. In short....Same old clunky, nearly impossible to use as ED intended stuff. ME should not have to depend on user work arounds for 50% of it's functions to work as they are suppose to. I have never gone into the Fallout LUA, or the COD LUA files to fix problems. Never had to.  I would go into the ME forum section and ask about all of this but I already know what I have to do because this problem has plaged the sim for years and years. And It's not my job to rework what ED should have already had worked out. 

 I have been here since 2000 or so.......Still stuff broken from waaaay back then. 

 Please ED.........Don't punish your base for being unhappy when they have every right to be. Just please fix some of these things. 

[Moriarty]

Can’t recall exactly how long ago this issue was marked as reported, locked and a comment added to the effect that there’s no timeline for a fix, but it’s probably due for that again.

[Hobel]

what exactly is the "Super slow .50 cal rounds redoux"?

[Miles Vorkosigan]

An issue that a simple lua edit could fix. It was reported soon after the module was released five years or so ago. THere was a very long running bug report thread going but recently all bug report threads are getting locked. So, this op started Part 2 here. 

[Nealius]

The lua fix isn't even possible on the user end anymore is it, given that they have now locked all weapons-related luas? Whatever happened to product maintenance and transparency? 

[Hobel]

9 hours ago, Miles Vorkosigan said:

An issue that a simple lua edit could fix. It was reported soon after the module was released five years or so ago. THere was a very long running bug report thread going but recently all bug report threads are getting locked. So, this op started Part 2 here. 

so the 50 cal fly too slowly and that was found out here with a relatively fast aircraft?

doesn't that also apply to the P51 or the P47?

and who says that the 20,13 or 30mm weapons of the german and british are not affected?

only there it is not so noticeable because the aircraft are slower.

 

I have always had a strange feeling about the speed of the weapons in the ww2 bird.

let's see if this can be confirmed

[71st_AH Rob]

1 hour ago, Hobel said:

so the 50 cal fly too slowly and that was found out here with a relatively fast aircraft?

No, this is specifically about the Sabre, the muzzle velocity of the .50 cal was set for the wrong ammunition type and for the earlier version of the M2 machine gun that was used in the Mustang not the M3 used in the Sabre.

 

This results in the rounds having too much drop so you need to lead the target with the Radar ranging gun sight and the AI Sabre mostly missing their targets.

[Wolf_ofthe_North]

The current in-game lua has them with an exit velocity of 830 m/s when research has shown it should be at least 870 m/s and more likely 890 m/s. More troubling than this is the inaccurately modeled ballistic characteristics of each round. This was pointed out by Curly in another thread, but basically he dug out books that indicate there should be waay less drop both before and after the transonic shockwave. 

[Squiffy]

Yes, it may just be that the "barrel warp" equation is worse than the lack of velocity. Some luas model the barrel effect with a circular dispersal. It's much easier to adjust it that way. Like on the Spitfire for example (and the Browning .303). The barrel warp is exactly the same between the MiG and the Sabre and we've been told the Sabre was based on the MiG so that it is somehow less objectionable. But the effect is way out of whack with nature as can be seen in gun camera footage and sighting photos from gunnery ranges with almost laser-like tracer paths on long exposure photos. 

 

I busted the warp equations down my like 75%. But another tweak which has served me well offline, is to adjust the max g rating on the MiG by 0.5 to 0.3 increments to simulate average g technique in the pilots without g suits. That really effects how much lead they can pull and how hard they can turn, and this helps bring the muzzle velocity aspect back into a more real world appearance. Also adjust your seat about as high as it will go to see down over the nose and "rope a dope" with tracers, pipper be damned.

 

The module was made by a third party so I am sure getting things changed is a "boring" and "old hat" task for developers who have moved onto new and exciting things.

I have never really played online and don't play much at all lately. I bought the F-16 and Spit IX lately but didn't fly them much probably because my old HOTAS Cougar is really worn and spikey. 

[Curly]

4 hours ago, Squiffy said:

Yes, it may just be that the "barrel warp" equation is worse than the lack of velocity. Some luas model the barrel effect with a circular dispersal. It's much easier to adjust it that way. Like on the Spitfire for example (and the Browning .303). The barrel warp is exactly the same between the MiG and the Sabre and we've been told the Sabre was based on the MiG so that it is somehow less objectionable. But the effect is way out of whack with nature as can be seen in gun camera footage and sighting photos from gunnery ranges with almost laser-like tracer paths on long exposure photos. 

 

The module was made by a third party so I am sure getting things changed is a "boring" and "old hat" task for developers who have moved onto new and exciting things.

It's both. The bullets have to much drag and the barrel heating penalties (accuracy and velocity drop) are to high.

 

However the MiG-15 also has issues with it's armament. The 23mm HEI shells don't fire. So the 23mm cannon only has half the ammo.  40 rounds not the 80 it's supposed to have. Also, the 23 mm AP rounds have their caliber set to 37 mm. Which I assume was a hack to get the 23 mm cannon to work. 

[BIGNEWY]

Appreciate you are frustrated, you can see we have reported it, and we are bumping the report internally, that is all we can do currently. 

 

Thanks

[Curly]

The gun heating due bullets fired model is incorrect.

 

TLDR Version:

 

The gun heating model has the wrong barrel and body mass. Resulting in a rapid rise in gun temps.  

 

The mass of the barrel in the game is 2.7 Kg. The mass of the real gun barrel is 10.6Lbs or 4.8kg.

 

The mass of the body in the game is 14.3 Kg. The mass of the real gun minus the barrel is  58.09 lbs or 26.34 Kg

 

There is too much heat per shot. The thermal energy input into the guns in the game is 7.823 Joules per bullet. Tests indicate the variable “shot_heat” should be from 4.62 to 4.023 Joules per bullet. 

 

The reduction in accuracy and velocity due to gun heating are too large. Tests of the Real gun barrel indicate that a burst of 365 bullets can be fired without a reduction in accuracy or muzzle velocity. And, that the accuracy and velocity life of the  M3 gun barrels are 8 times greater than that of the regular steel barrels.  

 

https://www.loc.gov/resource/dcmsiabooks.hypervelocitygun01bush/?sp=499

 

 

An accurate model for gun heating would look like:

 

{ name = "HeatEffectExt" , shot_heat = 4.62, barrel_k = 0.462 * 4.94, body_k = 0.462 * 26.34 },

 

With a 20% reduction in accuracy and reduction in muzzle velocity 200 fps being applied at a barrel Temperature of 800c or the equivalent of 350 consecutive shots. Having the guns fire uncontrolled ( a Cook Off model) after a 200 round burst or a body temperature of 900 C would be realistic too. 

 

For comparison the current gun heat model in the code is: 

 

{ name = "HeatEffectExt" , shot_heat = 7.823, barrel_k = 0.462 * 2.7, body_k = 0.462 * 14.3 },

 

Elsewhere in the code, the values of gun heating model  are explained for the 50 cal M2:

 

function M2_heat_effect() --[[ 7.823 kJ - one shot energy , 462 (steel specific heat), 6 kg - barrels mass ]]

 

{ name = "HeatEffectExt", shot_heat = 7.823, barrel_k = 0.462 * 6.0, body_k = 0.462 * 32.0}

 

The heat effect model contains 3 variables which describe the thermal dynamics of the gun. 

 

The First variable is,. shot_heat = 7.823, This energy input into per bullet fired. It’s set to 7.823 Joules per bullet fired.

 

The variables barrel_k and body_k are the thermal capacity of the gun barrel and body. This variable consists of two numbers: the specific heat of the material and its mass. 

 

For the F-86 Barrel,  the thermal capacity is, barrel_k = 0.462 * 2.7

.426 is the specific heat of steel and 2.7 is the mass of the DCS F-86’s gun barrel.

 

The specific heat of a material is the energy, in joules, required to raise the temperature of a kilogram of that material, by 1 degree C.The specific heat of steel is.462 joules per gram. 

 

Therefore, the energy (Joules) required to raise the temperature of the gun barrel 1 degree C is 

 

Joules Need to raise temp by 1c = mass of material * the specific heat of the material. 

1.2474 =2.7*.462

 

Since the code gives the heat input per bullet, 7.823 Joules, we can compute the change in barrel temp after 1 shot is fired. 

 

As the change in temp is = (Joules per Shot * Number of bullets fired) / (the specific heating of steel * the barrel Mass)

 

In terms of the Gun heat variables 

 

the change in barrel temp = (shot_heat = 7.823  * the number of shots) / (barrel_k = 0.462 * 2.7)

 

For one bullet the temperature of the guns increase by 6.27C 

7.823/(0.462 * 2.7)= 6.271C

The code tells us, The DCS F-86 is modeling a barrel with a mass of 2.7 kg which is about 5 lbs. The manual for the 50 Cal M3 machine gun.

. 

https://www.scribd.com/document/38654349/TM-9-2190-M3-Browning

Notes, the barrel weight is 10.91 lbs which is 4.94 kg. 

 

The DCS M3 machine gun barrel has half as much mass as the real one. It seems trivial, but the reduced mass has important implications due to the heat modeling.

 

If we model the gun with the correct barrel mass; the gun temperature increases 3.47C per shot. 

 

7.823/(0.462 * 4.94) = 3.4377C.  

 

This is just about half as much heat as is currently modeled 6.7C per shot. 

 

The code shows the weight of the body of the gun as 14.3 Kg which is also incorrect.  

 

body_k = 0.462 * 14.3

 

The weight of the gun body in DCS is 14.3 Kg or 31.5 Lbs, The M3 manual gives the weight of total Gun as 64 1/2 lbs + 4 1/2 lbs for the recoil adapter. So 69 lbs total. The total mass - barrel should give us the “body mass” 69-10.91. Or 58.09 lbs / 26.34 Kg. Again about half the mass of the actual gun is in the thermal model. So the body of the gun heats up twice as much as it should too. 

 

In DCS, the temperature of the gun body increases 1.184C for every shot. 

 7.823/(0.462 * 14.3) = 1.184C increase in temp

 

If we model the gun with real weight - barrel. The temperature of the body increases by .6428 C 

 

7.823/(0.462 * 26.34) = .6428c. 

With the correct body weight that shot per heat is reduced by half. 

 

If you’re ready for a deep dive on the metallurgy and  performance of 50 caliber gun barrels, read on. 

 

We’re going to compare the heat modeling of the DCS M3 to some real tests.The tests   indicate that the loss of accuracy and the drop in muzzle velocity as a result of barrel heat are too high in the DCS F-86.

 

The construction of the gun barrel used on the M3 machine gun is different from a standard steel barrel.  The properties of the materials used in the barrel of the M3 machine gun increase the number of bullets which can be fired before the accuracy or the muzzle velocity of the gun drops when compared to the plain steel barrel.

 

https://www.loc.gov/resource/dcmsiabooks.hypervelocitygun01bush/?sp=499

 

This chart shows how many M2 AP bullets can be fired on a severe firing schedule, before the muzzle velocity drops by either 200 fps or 20% of bullets impact yawed.

 

The chart shows that a steel barrel can only fire a single 170 burst. The lined and plated barrels, Which are on the F-86’s machine guns, did  a  350 round burst and two 500 round burst cycles, for a total of 1350 bullets before the accuracy of the weapon dropped.   

 

 

 

The test consisted of an initial burst of 350 rounds. The gun is then allowed to cool to room temperature. After the gun is cooled, a burst of 100 rounds are fired. The gun is allowed to cool for 2 mins and then another 100 round burst is fired. This cycle is repeated until 500 bullets have been fired. After the 500 round burst, the gun is allowed to cool to room temperature. The 500 bullet burst cycle is then repeated until either the muzzle velocity drops by 200 fps or the accuracy is degraded by 20%.The accuracy and muzzle velocity of the gun are measured periodically through the test. 

 

The model barrel of the M3 machine gun on the F-86, is the same design as the one tested in the chart. Stellite lined with chromium plating. 

 

 From the M3 weapons manual. The model of M3 barrel is 7265156 and it has the same type of lining and plating as the barrel tested in the chart. 

 

 

Page 23 of manual notes, the barrel has a 9 inch liner and is plated with chromium. 

 

A cross section of the barrel is available in the M3’s weapon’s inspectors manual. 

https://www.smallarmsreview.com/archive/detail.arc.entry.cfm?arcid=2758

 

And a color picture of the liner. 

https://apps.dtic.mil/sti/pdfs/ADA472711.pdf

 

The Manufacturing process of the Stellite / Cobalt liner. 

The 9 inch liner in the F-86’s gun barrel is made of Stellite 21.  An Air National Guard memo regarding the recycling of these barrels and liners verifies this.  

https://www.google.com/books/edition/National_Guard_Bureau_Bulletin/cYhat3J3bmUC?hl=en&gbpv=1&pg=RA7-PA7&printsec=frontcover

Note the same barrel model, 7265156, as indicated in the Manual for the M3 machine gun posted above.

 

The lining and plating of these barrels was developed during World War 2 to improve the accuracy and velocity of the 50 caliber aircraft machine gun. 

The development,  metallurgy, construction and testing of these barrels are discussed in detail in the National Defense Research Committee Report. 

https://www.loc.gov/item/2007498072/

 

Let’s look at the 9 inch Stellite line and see how this improves the performance of the M3 machine gun barrel.

 

The 9 inch liner is made of a cobalt alloy called Stellite 21. 

 

The Stellite / cobalt liner provides two primary advantages over the plain steel barrel. The cobalt liner has a higher heat hardness and is less prone to chemical erosion than the plain  steel barrel. 

 

The properties of the Stellite / Cobalt liner reduces wear inside the barrel and keeps the grooves (rifling) in the barrel intact. This increases the velocity life of the weapon. Meaning long bursts can be fired through a Stellite /Cobalt lined gun without a reduction in muzzle velocity.

 

The Stellite / cobalt barrel liner is so effective that it actually increased the muzzle velocity of the weapon. 

 

 

The Stellite / cobalt liner is so effective at preventing a drop in muzzle velocity during burst firing, that the limiting factor for burst length is the reduction in accuracy.   

 

  

Since the F-86’s gun barrels have this type of liner. There should be no drop in muzzle velocity for bursts shorter than 350 bullets.

 

 

The second benefit of the cobalt / Stellite liner was that it reduced the heat input into the barrel. Which helped to prolong the accuracy life of the weapon. Meaning more bullets could be fired through the barrel before the accuracy drops. 

 

 A 295 continuous burst could be fired through a Stellite / Cobalt lined barrel compared to 167 from a plain steel barrel, for the same loss in accuracy.   

This is because the cobalt liner is a worse conductor of heat than plain gun steel.

Less thermal energy per second is transferred from the Stellite / Cobalt liner into the gun barrel. 

 

The Cobalt / Stellite liner reduces the heat transfer into the barrel per bullet fired when compared to the plain steel barrel.

 

A 350 round burst test, on a 50 cal 36 inch aircraft barrel with just the 9 inch liner. Illustrates how effective the Stellite / cobalt liner is in reducing heat input into the steel barrel. 

 

The mean barrel temperature was measured to be 750 C after the firing. If we assume an ambient temp of 20c. The temperature of the barrel rose 730C after a 350 round burst.

 

For a 350 burst, The DCS thermal model for the F-86 gun barrel predicts a temperature increase of 2195c. 

 

(7.823* 350) / (0.462 * 2.7) =2195C.

 

That’s 3 times more than the test firing of a barrel the cobalt liner.

 

Based on the test data we can compute the thermal energy input into the barrel per shot for a 50 caliber machine gun with a Stellite / Cobalt liner. In game terms we can find the real value for the variable  “shot_heat =”  

 

Assuming 20 c ambient temperature. The temperature of the lined barrel increased by 730 degrees. Each shot increases barrel temp 2.0857C.

 

Temperature increase per  Shot

730/350 = 2.085714 c per shot

 

The energy input into the barrel per shot works out to:

Change in Temp =( Joules per shot *Shots fired) /( Barrel Mass * The Specific Heat of the barrel.)

Joules per shot = (Temp * ( Barrel Mass * The Specific Heat of the barrel))/ Number of bullets fired.

730=x*350/4.808*.462

730=350x/2.219

x=(730*2.219)/350 = 4.6282 Joules Per shot 

 

Testing of the aircraft barrel shows that the energy input into the barrel with the Stellite / cobalt liner is 4.6282 Joules per bullet.

  

The DCS model adds 7.823 Joules per bullet, 1.69 times more than the testing indicates.  

 

The reduction in heat transfer to the gun barrel is important because, reducing the temperature input into the barrel improves the accuracy during burst firing. 

 

As the gun barrel heats up, it expands. The expansion of the gun bore caused by heating is proportional to the linear coefficient of thermal expansion of the barrel material.

 

 Once the temperature of the gun barrel reaches 750c, The barrel expands to the point where the grooves (rifling) in the barrel do not engage the bullet. This causes the bullets to yaw and tumble in flight. Which reduces the accuracy of the weapon.   

 

 

The lack of grooves cut into the bullets 4, 5 and 6,  indicate the barrel has expanded to the point where it no longer produces accurate fire.  

 

In this test of a plain steel barrel a 100 burst was fired, followed by 2 minutes of cooling. Then a 100 round burst was fired.  After the second 100 burst all  the bullets from the standard steel barrel begin to  impact yawed / tumbled. 

 

In a burst test of the Stellite / cobalt lined barrel, the trigger is held down until the bullets begin to tumble and yaw in flight and impact, thus impacting sideways. The Stellite lined gun barrel can fire 350 round before all the bullets impact yawed.    

 

In this next series burst tests belts of combat mix ammo were fired.

 

The C-1 schedule is a continuous burst fired until 100 % impact sideways / yawed.

 

The Stellite lined barrel can fire a continuous burst of 295 bullets before the accuracy is degraded. Compared to only 167 bullets for the plain steel barrel.  

 

In another set of tests, a Settilte / Cobalt lined barrel was fired until the accuracy was reduced to the same point as the combat mix tests, 100% of the bullets tumbled / “keyholed”. The temperature of the barrel was measured to be 750C when all the bullets tumbled.

 

We’ll use the temperature data from this test and the burst length from the combat ammo test to calculate the heat input per bullet into the plain steel gun and the Stellite / Cobalt lined barrel when belts of combat ammo are being fired. 

 

From the temperature monitored heating tests, we get the coefficient of linear thermal expansion of the gun barrel. 16*10^-6 or 0.000016

 

The coefficient of linear thermal expansion = The change in barrel diameter /( the initial barrel diameter * the change in temperature).  This tells us how much the gun has to heat up to expand to the point where all the bullets tumble.

 

The coefficient of linear thermal expansion of gun steel (0.000016)  = The increase in barrel diameter due to heating  (.006)/ the initial diameter of the barrel(.5) * The change in temperature (750).  

 

0.000016=.006/(.5* 750)

This says for the barrel to expand .006 inches the temperature of the barrel has to be 750C. 

 

When the diameter of the gun bore expands .006 inches, The bore diameter is greater than the depth of the rifling, the grooves in the barrel. When the bore diameter increases by .006 inches,  The groves in the rifling no longer make contact with the bullet. No spin is imparted to the bullet and it tumbles in flight, resulting in a drop in accuracy. 

 

Since we know the barrel has to be 750c to expand enough for 100% keyholing to happen: The burst test conducted to 100% keyholing, provides us with a means to make a direct comparison of the two gun barrels. Since we can assume the barrel Temperature of both guns barrels was 750C when the test was stopped. 

 

*note the lower burst length in these tests is a result of the ammunition used. These bullets have a larger powder charges / higher muzzle velocity when compared to 50 Cal M2 AP ammunition 

 

We’ll  compute the energy input per shot for the steel barrel and Stellite / Cobalt lined barrel. 

 

Based on the law of linear thermal expansion and the previous testing. We can assume Both barrels were 750c when 100% keyholing / tumbling occured. 

 

The coefficient of linear thermal expansion of gun steel (0.000016)  = The increase in barrel diameter due to heating  (.006)/ the initial diameter of the barrel(.5) * The change in temperature (750).  

 

0.000016=.006/(.5* 750)

 

If we assume that the ambient temperature of the guns was 20 C,

We can solve the specific heat equation, to determine the energy per bullet needed to raise the barrel temperature  730c  to 750C.  

 

Let's look at the steel barrel first and compute the energy input per shot.    

 

Barrel Temperature = ( Joules Per Shot * The number of shots)/ (Specific heat * The barrel Mass. 

730 =( x * 167) / (.462 * 4.807)

 

Joules per shot = (Temp * ( Barrel Mass * The Specific Heat of the barrel))/ Number of 

bullets fired.

 

9.707 = (730 * 2.220834)/ 167

 

9.707 Joules per bullet are transferred into the barrel when fired from the plain steel gun.

 

The Stellite / Cobalt lined barrel reaches  750c after firing a 295 round burst. 

 

Therefore the energy input per shot is 

 

(730 * 2.220834) / 295 =5.495 Joules per shot.

 

The Stellite / Cobalt liner reduces the thermal energy transferred into the barrel by 56%. 

 

On a per shot basis, the barrel of a Stellite / Cobalt does not heat up as much as a regular steel gun. Therefore the barrel of the Stellite barrel expands less than the regular barrel per shot. Thus over a large burst, the Stellite barrel is more accurate than the plain steel barrel.    

  

While the accuracy and velocity life improvements resulting from the Stellite/ Cobalt liner to gun are impressive. The performance of barrels of the M3 machine gun were also improved by their Chromium plating.  

 

The development and testing of the Chromium plating is covered in the same NDRC report. 

 

 

The Chromium plating also improved the velocity life and accuracy life of the gun barrel. However Chromium plating primarily  improved accuracy of the gun. 

 

 

 

The Chromium plating of the barrel chokes the bore. Meaning the plating reduces the bore of the gun near the muzzle. The bore  of the Chromium plated barrels is reduced from .5 inches near the breech to .492 inches at the muzzle.

 

 

This reduces the loss accuracy due to heating. Going back to our calculations of the linear thermal expansion of the gun.  We can calculate the temperature need to increase the narrow barrel diameter to the original diameter .5

 

Since the linear coefficient of expansion is intrinsic to the gun barrel material. 

algebraically we can compute the temperature needed to make the Chromium barrel expanded from .462 to .5 inches or .006 inches

 

Coefficient = material expansion/(Bore of the Gun * temperature of the gun.)

0.000016=.006/(.492* x)

Temp =  ( expansion / Coefficient * Bore)

762.1951 =.006/(0.000016*.492).

 

In the report it’s noted that the temperature required to increase the muzzle diameter of the plated barrel to .5 inches is 800C

 

Tests of the Chromium plated barrel indicate that 319 consecutive bullets can be fired before the accuracy is degraded.

If we assume 800 C is the critical temperature for this accuracy reduction and 319 bullets are fired we can compute the number if Joules per shot fired were fired to reach 800C. Well assume the ambient temperature is 20C and compute the Joules per bullet based on a 780 C rise in barrel temp. 

 

Joules per Bullet = ((Barrel Mass * Spec Heat) * Change in Temperature) / The Number of Bullets fired.

 

5.42 = ((4.807 * .462)* 780) / 319

 

The accuracy of the Chromium plated barrels was remarkable when compared to the accuracy life of the plain steel barrels.  On the same 100 round burst 2 min of cooling schedule. The line barrels can fore over 1000 rounds without a reduction in accuracy. 

 

The plain steel barrel, on the same firing schedule, loses accuracy halfway into the second 100 round burst.  

  

The chromium plating also helps to reduce the heat input to the barrel, While not as effective as the Stellite / Cobalt liner, it still helps. Temperature monitored tests of the barrel give an indication of the effect. 

 

The plated barrel was seen primarily as an accuracy enhancement, While the Stellite / Cobalt lined barrel was seen as velocity enhancement. Since the two improvements were complementary, The Stellite liner was combined with Chromium plated barrel to provide a gun with the best features of both materials. 

  

 

When the Stellite / Cobalt liner and Chromium plated were combine, the barrel was known as a “combination” barrel.

 

 

 

The performance of the combination barrels was remarkable. The guns equipped with these barrels, could be fired without a loss of accuracy and minimal velocity drop until the barrel melted. 

 

 

 

Given the increased performance of these barrels, why does the 50 Cal M3 have a 200 round burst limit? The burst limit is not the result of decreased velocity or accuracy. The burst limit is pure a function of the cook temperature of the ammunition.

 The  manual for the 50 caliber M3,  actually notes ``The treatment of the barrel gives it exceptional velocity and accuracy life, but does not affect the cook off point.” 

 

A cook off is an uncontrolled firing of a bullet inside of the gun. 

https://www.smallarmsreview.com/archive/detail.arc.entry.cfm?arcid=13265

 

The cook off point is temperature in the breach which will cause the bullet to fire on its own, without a trigger pull.  The M3 weapons  Manual notes that a 200 burst is the cook off limit. 

 

The NDRC report gives the temperature above which a misfire / cook off  can occur.

 

 

900 F = 482C  the cook off temp. Using the specific heating capacity of the real gun we can calculate how many bullets in a burst it would take to heat the gun up to 482 C. We’ll assume the ambient temperature of Barrel is 20 C.    

 

The barrel reaches the cook off / misfire  temperature after a burst of 221 bullets have been fired.

 

As the number of shots fired = ((Barrel Mass * Specific Heat) * delta Temp) / Joules Per shot 

 

Assuming the ambient temp of the gun is 20 c. The temp has to rise 462C to reach 482C, the cook off temp. 

 

221.6 = ((4.807 * .462) * 462) / 4.63

 

By using the test data, we can compute the burst limit within 21 rounds of the limit given within the manual.  When we compare the burst limit to the performance tests of the real gun barrels, it is obvious that the burst limit of the F-86’s are not reflective of a performance drop of the guns.

f86 gun heat .trk

Edited May 27, 2022 by Curly
formatting

[Art-J]

Could you please re-format your post text colour? I suspects it's an interesting post with lots of data in it, but for those of us who use "dark" forum theme it's unreadable because it displays black text over dark grey background.

Edited May 27, 2022 by Art-J

[BIGNEWY]

Hi, 

I will ask the team to take a look. 

thanks

[SmirkingGerbil]

I am just here for the sheer amount of information, and work that went into this write up.

 

 

[MiG21bisFishbedL]

Curly put in his work. It's too bad ED isn't reciprocating here. 

[NineLine]

This is fixed internally, hopefully, you should see it in the next patch release.