MK 108 Shells too slow

[amazingme]

there you go

 

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

 

Best I can do here:

 

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

Muzzle 485 2820 -5 0 0 0 0 0

50 474 2690 0 0 0 0 0 0

100 462 2564 -6 2.1 0.6 0 0 0

150 451 2443 -23.6 5.4 1.6 0 0 0

200 440 2325 -53.6 9.2 2.7 0 0 0

250 429 2211 -95.8 13.2 3.8 0 0 0

300 419 2102 -152.4 17.5 5.1 0 0 0

 

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

Muzzle 540 3496 -5 0 0 0 0 0

50 528 3342 0 0 0 0 0 0

100 516 3194 -3.8 1.3 0.4 0 0 0

150 504 3050 -17 3.9 1.1 0 0 0

200 493 2912 -40.1 6.9 2 0 0 0

250 481 2779 -72.9 10 2.9 0 0 0

300 470 2650 -117.1 13.4 3.9 0 0 0

Edited January 11, 2017 by amazingme

[rel4y]

Well what BC did you use and how did you arrive at it? Do you think you get away with googling a ballistic calc and then hornady does all the thinking for you? Why on earth did you include winddrift in he first one and are these at ISA values? :D

 

Why does your 30 mm shell have less E0 than a .308? So many mistakes..

Edited January 11, 2017 by rel4y

[amazingme]

We can re-invent the wheel if you want and we can get as deep as you want in analysing the data. Your call..

P.S. G7.. of course

[Enduro14]

why are you guys having a weiner contest on ballistics???? Who cares, if we have identified some errors then lets get it consolidated and put in the right channels for a fix.

 

So is the 30mm the germans used a boat tail hollow tip? I know quite allot in the sniper realm this stuff aka the aircraft i do not. As interesting as this discussion has been i think we should focus together and list exactly what deficiencies their are if any yes???

 

If you want i can use my Applied ballistics kestrel tomorrow and see what it says if it helps at all?

[rel4y]

Does your kestrel support 30mm ammo? Otherwise you would need to manually input the BC. The shells look like that:

 

amazingme says this is a blunt lead nose (apparently called G7 at hornady)

 

Edited January 11, 2017 by rel4y

[amazingme]

The point is that the modelled shell is behaving rather peculiar and we want to find out why..at least that's my case.

[amazingme]

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

 

The question for ED would be what data exactly they use to calculate the shell trajectory..

[Enduro14]

Does your kestrel support 30mm ammo? Otherwise you would need to manually input the BC. The shells look like that:

 

amazingme says this is a blunt lead nose (apparently called G7 at hornady)

 

 

yes you can custom build any ordinance you want on the G scales. Plus they have many pre made profiles which honestly i doubt they have this round but ill look. It will be a fun side project, wish i would of brought it home today.

 

disclaimer i dont speak german so ill do my best to figure that diagram out.

 

:thumbup:

Edited January 11, 2017 by Enduro14

[Enduro14]

The point is that the modelled shell is behaving rather peculiar and we want to find out why..at least that's my case.

 

I agree with both of you its a very in depth and great conversation just minus the im smarter more qualified than you stuff. Because joint effort here could really bring some great info into the mix and maybe even lead to further changes with "other" ordinance in the sim. :)

 

 

http://www.appliedballisticsllc.com/Articles/ABDOC106_BCTesting.pdf

 

in mean time this is a good read, much much smarter People out their than me that have enhanced our capabilities in the last 10 or so years. For example we use to use the g1 scale for a boat tail hollopoint type round for long range, then finally light bulb G7 is what should be used.

Edited January 11, 2017 by Enduro14

[rel4y]

You can derive the BC from the ballisticc table I posted earlier. The kestrel should support that. Its more precise than these G profiles for small arms.

[amazingme]

+1 for the "minus"

[rel4y]

Sooo I quickly ran the calculation and arrived at an BC of 0.332. :) Let me hear what you get.

[Enduro14]

You can derive the BC from the ballisticc table I posted earlier. The kestrel should support that. Its more precise than these G profiles for small arms.

 

Just so i understand your saying the table you posted would be more accurate than the Kestrel? Either way what would be interesting with the kestrel is i can set the density altitude to that of what the aircraft would be flying and any other environmental factors and ranges get data as far as bullet drop, and all phases of flight hence speed and when it more than likely would start to tumble aka trans sonic to sub sonic depending upon the rounds design and aerodynamic properties.

[Enduro14]

Sooo I quickly ran the calculation and arrived at an BC of 0.332. :) Let me hear what you get.

 

will do unfortunately it will have to wait till tomorrow afternoon Germany time.

 

http://www.bergerbullets.com/a-better-ballistic-coefficient/

 

this another good little article to help understand some of the Terms thrown out in this thread

 

A question for those with maybe real world combat aircraft experience and what not, what is the standard or desired BC of the rounds for aircraft?

Edited January 11, 2017 by Enduro14

[rel4y]

Well if using the Rechlin charts you need to stay at ISA, so altitude at 0. The kestrel is probably using the same calculations that all ballistic calculators are, so shouldnt be much of a difference. I dont really know how you want to use your kestrel without BC input? I dont think there will be presets for german WWII ammo?

 

Sorry made a stupid imperial units conversion mistake.. Try 0.852 as BC. 0.332 looked awfully low for such a massy projectile. This is for a G1 drag curve btw.

Edited January 11, 2017 by rel4y

[Enduro14]

Well if using the Rechlin charts you need to stay at ISA, so altitude at 0. The kestrel is probably using the same calculations that all ballistic calculators are, so shouldnt be much of a difference. I dont really know how you want to use your kestrel without BC input? I dont think there will be presets for german WWII ammo?

 

I can use the BC you just came up with or a custom one aka it has the ability to build cutomized bullet profiles no matter what the size. Biggest thing i would need to know is this round more suited for a BC scale in G7 or some other scale. So ya we can use just what a standard ballistic calculator outputs and or what the old german data is. That only takes you so far, that is a base as you know.

 

So i just know from real world stuff what a calculator says without real world environmentals doesnt get you on tgt, so im curious how the AIR to AIR guys did this stuff.

 

So this leads me to this Does DCS take in effect the altitude and enviromentals for the ballistics? If not then i can see a simple comparison to the base charts is all we need then...?

[Enduro14]

Well if using the Rechlin charts you need to stay at ISA, so altitude at 0. The kestrel is probably using the same calculations that all ballistic calculators are, so shouldnt be much of a difference. I dont really know how you want to use your kestrel without BC input? I dont think there will be presets for german WWII ammo?

 

Sorry made a stupid imperial units conversion mistake.. Try 0.852 as BC. 0.332 looked awfully low for such a massy projectile. This is for a G1 drag curve btw.

 

Ya i was going to say that was a crazy low bc and would never want to shoot that personally LOL. .852 sounds like what i would expect. Ok what i will do tomorrow i will build the bullet in my Kestrel in both the g1 and g7 scale and see what we get for fun.

[rel4y]

Both G1 and G7 drag profiles will give good approximations. G1 will in my opinion be closer.

 

I can tell you that the delta v0 is modeled with an 0,8% randomization, but if altitude effects are modeled.. no clue. ;)

Edited January 11, 2017 by rel4y

[DefaultFace]

190 seems to allow you to adjust the sight for different altitudes. Not sure if it works though.

[Enduro14]

190 seems to allow you to adjust the sight for different altitudes. Not sure if it works though.

 

Thats very interesting.... ED, YO-YO any input on that??

 

PS does somebody have the barrel length and twist rate of the specific Cannon that is in the 109?

 

 

so found this on a historic sight

 

"MK 108 a low muzzle velocity of 500-540 meters (1640-1770 feet) per second. The maximum rate of fire was 650 rounds per minute".

 

This is a very low muzzle velocity due to its very short barrel length, still havent found the dimensions yet.

 

http://www.luft46.com/armament/mk108.html

 

the rounds?

 

http://www.eeoda.de/2008/0804_FB1_MunMK108.pdf

Edited January 11, 2017 by Enduro14

[rel4y]

Which dimensions do you need?

 

Btw quickly ran the calc for v0 delta of 20 m/s, the difference in drop is around 27 cm at 400 m.

 

The difference for delta 40 m/s (500 vs 540 m/s) is 1 MOA at 100m, so 67% of the gun dispersion at that range. Like I said earlier... this is kinda sensless.

Edited January 11, 2017 by rel4y

[Enduro14]

Which dimensions do you need?

 

the actual barrel length of the weapon and then the twist rate, this weapon really reminds me of our mk-19 in a way. Very low velocity and your basically lobbing rounds in on tgt so its intriguing to me that their was a downward compensation in the barrel in the ME/BF-109. But then again maybe it makes sense since the aoa at altitude and engaging high altitude bombers makes sense???

 

so if you look at this http://www.luft46.com/images/mk108-3.gif

 

look at the side view left, from the tip of the round in chamber need the length from that tip to end of barrel. Im assuming it has to have some sort of barrel twists also..

 

so is 23 inch barrel correct? Via the Lua's does it annotate anywhere this sort of specifications? 23 inch barrel is what i have found for the real world mk108 have not seen anything in reference to rifling/twist rate

Edited January 11, 2017 by Enduro14

[Enduro14]

Which dimensions do you need?

 

Btw quickly ran the calc for v0 delta of 20 m/s, the difference in drop is around 27 cm at 400 m.

 

The difference for delta 40 m/s (500 vs 540 m/s) is 1 MOA at 100m, so 67% of the gun dispersion at that range. Like I said earlier... this is kinda sensless.

 

I agree with you especially considering the tgt they where going after, B-17, So essentially it would be a difference of lets round it up to 11 inches at 400m from the dcs of 500m/s to real world stats of 540m/s . So talking about SMOA, shooters minute of angle 11 inches at 400m is just under 3moa of difference.

This in my world would not be acceptable but assuming air to air its a much broader shot group they are looking for i would say ok.

 

One thing i am interested in is if pressures in dcs actually effect the rounds ballistics?

Edited January 11, 2017 by Enduro14

[DefaultFace]

I don't think drop is really the key thing to be talking about with aerial gunnery here. The travel time of the projectile to reach a certain distance would have a more of an effect on how much lead is required, which is part of what makes the 108 difficult to use.

[Enduro14]

I don't think drop is really the key thing to be talking about with aerial gunnery here. The travel time of the projectile to reach a certain distance would have a more of an effect on how much lead is required, which is part of what makes the 108 difficult to use.

 

True.. considering we are constantly spit balling the lead required to hit tgt and if the sight currently has no good zero point it certainly could be a problem.

 

Things i would be interested to know from the real world pilots or those much smarter than me, with the sight in the 109 i assume... the sight is bore sighted and or zeroed for the MG's. If that is the case what is the MIL hold for the mk-108? So if at the insert perfect range you hold dead center for MG's your aim point for the MK-108 would be say at the 10 mil line low for example.

So in simpler terms what is the mil hold over for the mk-108, or is it essentially the same hold on the sight but just at closer range?

 

Time for me to RTFM lol

Edited January 11, 2017 by Enduro14