In the part were it says they were replaced by 151/20's or removed all together, I don't know how effective a slow firing cannon with low velocity is going to go with later war higher speeds when they were replaced in 1940 for that very same reason.
UK goes all-in on a HMG class gun in the mid-30'ies
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Interesting to note that even to this day it seems it's not a settled issue which kind of shell is best for an aircraft gun. The Mauser BK 27 shoots mine shells, whereas the 25 mm gun in the F-35 has a new "APEX" multi purpose shell, see https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2014/armaments/Wed15439Sande.pdf
Mine shells caused superficial damage on heavy structures but significant damage on lighter ones, AP round caused superficial damage on light structures but were devastating on heavier ones, I think the British got it right with a mix of SAPI and API in the Hispano and AP and incendiary in their .303's.
Claim is made about 'they didn't get much love in the Fw 190', yet you have no quote to back it up.
Alas.
Any definition of what constitutes as 'slow firing' and 'low velocity' and where the MG FFM stood there?
Glider
Captain
While its true to say that there is no quote that says 'they didn't get much love'. Its also true to say that the FF was replaced as soon as was practical in most German fighters. Mainly coming back into favour in NF where its compact dimensions were very important and the range very close.
Maybe Slower firing and slower MV would be more accurate
FF
MV between 585 and 700 m/s
ROF approx. 530 rpm
Hispano 20mm II
MV 840 m/s
ROF approx 600rpm
151/20mm
MV 800m/s Mine, 700m/s AP
ROF 750rpm
It says exactly that in the very link you posted. The FF was a stop gap solution in the Emil because it fitted in the wings where's the 151/20 didn't, furthermore if you read up on the FF you will notice it's compact size and lightweight were the leading contributors for its use more than anything else, that's especially true of it's use in night fighters.
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The link posted about the FF being fitted to the FW190 also quotes them being replaced by the 151/20 or removed entirely, sounds to me the pilots had a very low opinion of them hence my term they didn't get much love.
MG FF and FFM were certainly not ideal weapons. Despite not being ideal, they helped racking the scores of LW fighter force - even if we account just for day fighters - by many hundreds, if not in low thousands. Sorta Hawker Hurricane, Pz-IV of the 'French 75mm' amongst the onboard weapons.
Thank you.
By the time MG 151/20 was in service, the FFM was in use by a full year, able to do indeed 700 m/s with M-shell. The Bf 109F was criticized, eg. by Galland, for lowering the firepower vs. the 109E3/E4, 1060 rd/min vs. 750 rd/min as far as cannons go; crticism was also repeated once the LW found out that Spitfire was sporting two, and later 4 cannons, so LW went with gondolas on the 109. Trick with MG 151 was that it was not an easy fit within the confines of the wing of the 109 due to the size of the weapon, thus the gondolas, with increased both drag and weight by a notable amount.
The MG FF and FFM weighted 26 kg each, vs. 43 kg MG 151 each - not gonna break the bank, but it starts to matter once multiple cannons were being added to the fighters
Yea, right.
Adding two and two together to arrive at five?
Thats only the Mine shell and it wasn't interchangeable with the other types of ammunition in use, the reason for the FF/M designation.
And I quote from your source ( Early variants of the Fw 190 (A-1 to A-5) were typically fitted with an inboard pair of MG 151 and an outboard pair of MG FF/M, although the MG FF/M were sometimes removed in the field in order to save weight ).
A.G. Williams
Airman 1st Class
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- Oct 10, 2020
It can be quite tricky comparing weights like this. One point to bear in mind is that while the MG 151 had a built-in belt feed, the MG-FF needed a magazine feed which added 8 kg to the overall weight (or 12 kg for the 90-round drum).
Edit to add - I forgot about the MG 151's belt links; 60 links weighed about 1 kg.
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Glider
Captain
My understanding which certainly could be wrong, was that the criticism of the firepower of the F2 was the reduction to a single 15mm cannon plus the two LMG. The first example of a 109F captured by the RAF had the 15mm removed and a 20mm FF installed instead. Once they upped it to a 151/20mm most of the negative comments went.
I am sure that you are aware that the addition of the Gondolas was to do with attacking USAAF four engine bombers where 1 x 20mm and 2 x HMG wasn't sufficient. This also drove the replacement of the centreline 20mm with a 30mm.
A.G. Williams
Airman 1st Class
- 182
- Oct 10, 2020
It's a bit more complicated than that. The HE-T in the MG-FF weighed 134 g and was fired at 600 m/s. The M-Geschoss weighed 92 g and was fired at 700 m/s, but this did not generate enough recoil to work the MG-FF mechanism, so the gun had to be modified (and was renamed MG FFM), after which the MG-FF ammo could no longer be fired safely in the MG-FFM as it was too powerful.
However, the early M-Geschoss shell had no provision for a tracer, so the engineers worked out a compromise loading: this was an old-fashioned pre-M-Geschoss HE-T shell, modified to have a light-alloy (instead of brass) fuze body which reduced the weight to around 115 g. This was still too strong for the FFM, so the propellant was reduced, resulting in an MV of 585 m/s. They then made API shells for the FFM which also weighed 115 g (there's a picture of one in the group photo above).
Shortround6
Major General
You are right but the 115gram shells were good for about 585ms.
From the MG 151 the 115 gram projectiles were good for 710ms for and the 92 gram shells were good for 800ms.
However there was problem with both guns, The 115gram HE-T rounds had to be set up to stay close to the light weight 92gram shells which had the ballistics of a Ping-Pong ball.
The 92 gram shells lost velocity quickly. and at some point was going slower than the heavier shell.
The older FF cannon actually had a MV of 500ms with a 130-134gram shell. Started slow but kept it's velocity better.
At high altitudes in thin air the velocity didn't drop off as bad. Poor German pilots were trying to keep track of different projectiles with different times of flight from different guns (and the 7.9mm and 13mm guns were off just a bit from anything else, and each other)
Shortround6
Major General
The lack of strength that A.G. Williams is referring to is the weight of the breech block/recoiling assembly and the main spring was too light to keep the round in the chamber for the required time for the chamber pressure to drop. When then breechblock opened up 'early' the high pressure could blow out the side of the case and let high pressure gas back into the gun action/feed way/ejection chute. Even dissipating it does not take much pressure to bulge/break a drum or blow wing panels off the gun bay.
You are certainly right that drum added weight.
OTOH, the MG FF and FF fired the lighter ammo than the MG 151/20, by about 10%.
The gondola-outfitted Bf 109s were deployed in the east (Soviet test of the "five-gun" 109G-2 is well known) and in the MTO while Axis still had the foothold in Africa. Already the 109Fs were carrying gondolas in some occasions.
I was going to say words to that effect but it was too much typing, it's fair to say the FF and FF/M were a mess in 1940 and not the all powerful armament they were made out to be, the RAF decision to stay with the eight .303's was the correct one.
Just to add not only did the different 20mm shells have different ballistic paths they also shot to a different point of impact to the 8mm MG's, the Emils guns were a dog's breakfast in the BoB, just my opinion.
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- #119
Evidently they didn't think the concept was entirely without merit, as the introduction and wide usage of the Mk108 later in the war shows.
