Author Topic: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig  (Read 8754 times)

Offline bustr

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MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« on: March 16, 2012, 08:18:28 PM »
For the past 2 years I've been searching for available documents on the internet to understand the ballistics of the MK108 30mm. I've only found two testing results documents, one from testing at Rechlin E6 and one from Rheinmetall-Borsig themselves. I've recently run the data I have through a modern ballistics calculator and found some mistakes in my interpritation of the measurment units used in the documents. The units in the documents assume a common knowlege of the time so no unit legends are included in the documents.

The Borsig document included a Gyroscopic Right Hand Spin Drift chart for the 30mm round which I have been applying the wrong unit of measurment to their numbers. This is what caused me to find a modern ballistics calculator that produced spin drift results to correct my mistake.

I've converted meter and centimeter values to feet and inches for Drop, Dispersion and Spin Drift.
-------------------------------------------------------------------------------------

MK108 30mm Ballistics

Projectil Type - 3 cm Minengeschoss 108 Ausführung A mit Zerleger
Projectile Weight - 330g +-8
Projectile Length - 146mm (5.7in)
Initial Velocity - 500 m\sec (1640 ft\sec)
Barrel Firing Angle - 0 degree
Length of Barrel - 26 inches
Length of Riffling in Barrel - 21 inches
Rate of Right Hand Twist - 1:16
 

Range(M)..m\sec...ToF.....Drop......Disp......RH.Spin.Drift
0..............500........0.. ......0..........0........... 0
50............486....(.10s)...(2in).....###.......(1.7in)
100..........472....(.21s)...(8in).....(6.8ft).....(3.7in) <---- 109 yards
150..........459....(.31s)...(1.5ft)...###.......(5.9in)
200..........446....(.42s)...(2.7ft)...(14.0ft)....(8.4in) <---- 218 yards
250..........434....(.54s)...(4.4ft)...###........(11.0in)
300..........422....(.63s)...(6.5ft)...(21.9ft)....(1.1ft) <----- 328 yards
350..........411....(.77s)...(9.0ft)...###.......(.1.3ft)
400..........400....(.90s)...(12.0ft)..(30.2ft)...(1.6ft) <----- 437 yards
425.......................... ............................. ..(1.7ft)
450..........390....(1.02s)..(15.5ft)..###.......######
500..........379....(1.15s)..(19.6ft)..(39.2ft)..######
525.......................... ............................. ..(2.25ft)
550..........370....(1.29s)..(24.0ft)..###.......######
----------------------------------------------------------------------

You can see why tilting your barrel(Convergence) up inside of the DB605 and Ju213 hollow airscrew shafts for a zero of 250 yards in the game causes you to shoot realtively flat to 250 yards. It's the dispersion that screws your aim.

By the way I'm still looking for the german armerors manual that details the exact tilting procedure inside of airscrew shafts and what the adjustable mounts look like. It took me 2 years to get to this data, I can keep looking. So far all of the manuals I've translated detail with "Strong Warnings" for MG151/20 and MK108 about harmfull results, to make sure the cannon is bolted centered in the airscrew shaft.

I'm sure they are out there.
bustr - POTW 1st Wing


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Offline Rob52240

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #1 on: March 16, 2012, 09:29:22 PM »
Thanks for taking the time to research.
<S>
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Offline Scherf

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #2 on: March 17, 2012, 12:43:07 AM »
Good research, wtg.

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Offline Noir

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #3 on: March 19, 2012, 09:37:40 AM »
damn, 330g  :huh
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Offline VonMessa

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #4 on: March 19, 2012, 09:46:54 AM »
Good stuff  :aok
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Offline PR3D4TOR

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #5 on: March 19, 2012, 10:40:26 AM »
damn, 330g  :huh

Yep, it's basically a hand grenade's worth of boom.
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Offline Noir

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #6 on: March 19, 2012, 11:10:30 AM »
Yep, it's basically a hand grenade's worth of boom.

I've always been impressed by the aces high lancasters, soaking them like if it was 50cal  :noid but that's another story
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Offline titanic3

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #7 on: March 19, 2012, 11:26:02 AM »
I've always been impressed by the aces high lancasters, soaking them like if it was 50cal  :noid but that's another story

Wingtip seems the easiest way to kill a Lanc.

As for the OP, very nice work. Im can't imagine why a round to the engine block wouldn't blow the front quarter of the plane to pieces or at least take the propeller off. Instead, the result is usually a dead engine or a oil hit.

  the game is concentrated on combat, not on shaking the screen.

semp

Offline Charge

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #8 on: March 19, 2012, 12:03:16 PM »
The HE round is unable to penetrate the engine and as it is triggered upon entering the engine compartment what it probably does is that it blows off the engine cowling and possibly makes a few smaller holes to engine cleaning all the adjacent tubing and wiring away. After all it's all about pressure build-up. If the round would enter the engine before exploding and use that space for pressure to build-up and when blowing up add all that fuel in the engine and the result would probably be quite spectacular.

The AP would be a bit different. Imagine a 30mm AP through an engine running at full revs and breaking the crankshaft in two. The engine itself would probably take care of the rest... But there were no AP for fighters.

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Offline titanic3

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #9 on: March 19, 2012, 12:10:53 PM »
I'm gonna start flying a Hurri2D then. I better get 1 shot 1 kill.  :noid


  the game is concentrated on combat, not on shaking the screen.

semp

Offline Noir

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #10 on: March 19, 2012, 12:17:42 PM »
The HE round is unable to penetrate the engine and as it is triggered upon entering the engine compartment what it probably does is that it blows off the engine cowling and possibly makes a few smaller holes to engine cleaning all the adjacent tubing and wiring away. After all it's all about pressure build-up. If the round would enter the engine before exploding and use that space for pressure to build-up and when blowing up add all that fuel in the engine and the result would probably be quite spectacular.

The AP would be a bit different. Imagine a 30mm AP through an engine running at full revs and breaking the crankshaft in two. The engine itself would probably take care of the rest... But there were no AP for fighters.

-C+

ok, but in aces high, a 30mm hit will kill a fighter's engine, whatever the model.
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Offline titanic3

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #11 on: March 19, 2012, 12:28:17 PM »
ok, but in aces high, a 30mm hit will kill a fighter's engine, whatever the model.

It will kill the engine but not blow it apart. Almost all my tater kills are wings, tails or fires. There is explosion every now and then but it's mostly due to killing the pilot (which has the same effect). And you can easily tell if it's a pilot hit due to the orange flash. Only very rarely will a plane explode due to a non-pilot hit (I hit the bottom of the plane, or where the fuel was leaking). So rough estimate:

90% - wings, tails
8% pilot kill
2% explosion

  the game is concentrated on combat, not on shaking the screen.

semp

Offline Noir

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #12 on: March 19, 2012, 12:38:21 PM »
I was pointing the different treatment between bombers and fighters. I always whine about the bombers toughness , including the A20. Sorry for the thread hijack ^^
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Offline PR3D4TOR

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #13 on: March 19, 2012, 04:39:12 PM »
British test firing of the MK 108 against a Spit:

http://www.youtube.com/watch?v=ZoLLDi-M3fk



Not much left of that 17...  :uhoh

http://www.youtube.com/watch?v=rDOAb_E8EtU
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Offline bustr

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Re: MK108 30mm Ballistics from Rechlin and Rheinmetall-Borsig
« Reply #14 on: March 19, 2012, 09:21:58 PM »
HoHun, Tony Williams colleague explained that the spitfire and blenhiem tests were performed against multiple airframes and the pictures and films we see today are of the most dramatic results. The British did not understand how the Mineshell worked opposed to their HS20mm HE or HEI. In the Mineshell testing the results were that 30% of the airframes were kills and the rest unservicable.

The 20mm HE had a thick steel caseing which combined kinteic penetration due to the fuse timing then an explosion that threw around large slow chunks of the casing. I beleive the common explosive was 6-11 grams of TNT.

The 3 cm M-Gesch. 108 Ausf.A m. Zerl. had 85 grams of HA41 (hexogen aluminium) or 85 grams of penthrite. I've seen mostly HA41. The Stielhandgranate 24 stick grenade has 165 grams of TNT. HA41 is roughly 2.5x more energetic and explosivly burns 2x of TNT. TNT - 900c vs. HA41 - 1800c. The NS-37 HE had about 27 grams of TNT with a thick steel casing.

What the British did not understand about the Mineshell was the highly energetic explosion turned the thin steel caseing into tiny, sharp, very high speed shards that blew through aluminum skin, control cables, internal structures and crewmen like knives. The 8th Airforce performed tests on a B24 and determined the shell casing performed more damage than the explosion.

The Mineshell 30mm did not need to penetrate the aluminum skin due to the high speed steel shards. The photo of the B17 looks like the mineshell entered the open gunners window exploding inside which accounts for the amount of blast damage(85g HA41) and bulging. The Mineshell was being used since the BoB in Bf109E 20mm for the explosive shard damage effect against BoB British fighters. The germans used a collection of rounds in the 13mm-20mm knowing what the combined effects would be. Look in the back of Schiessfibel for a visual explanation.

The 3 cm M-Gesch. 108 Ausf.A m. Zerl. going off against the tail, body and wings of aircraft should be slicing up important structures underneath the aluminum skin. The least of which shreading oil lines, fuel lines and cutting control cables. Even wounding or killing the pilot and crew. If it happens to penetrate the skin before detonation, it should go off like a stick grenade pushed into the aluminum skin then the pin pulled. From reading, the sense I get about HE type fuses in general is explosion was at contact or there was just enough delay for the round to force into the aluminum skin allowing the detonation to expand into the ariframe cavety. Granted angle of attack to the aluminum surface could cause a bounce away or surface explosion relying on the casing shards to perform damage. HEI and SemiAP HE will have a delayed detonation fuze to allow full penetration and not used in the same rational as a Mineshell round. 
bustr - POTW 1st Wing


This is like the old joke that voters are harsher to their beer brewer if he has an outage, than their politicians after raising their taxes. Death and taxes are certain but, fun and sex is only now.