Author Topic: MGFF/M vs. Mg151 (Read 2820 times)

Heinkel · « **on:** June 15, 2002, 09:51:53 PM »

First read these...

MG FF/M:

The MG FF/M was a motor cannon with 20 mm caliber. This gun was manufactured in Germany under licence, but it was developed by Oerlikon in Switzerland. The MG FF/M was 1338 mm long at a weight of 26,3 kg. The cadence of this weapon was 540 rounds per minute at max, the speed, the projectiles got, leaving the muzzle was 700 meters per second.
The cartridge had a weight of 202 g, 134 g apportioned to the projectile. The ammunition was stored in magazines

MG 151/20:

To increase the power of MG 151, Mauser deveoloped 1937 a design with 20 mm caliber. This re-designed Weapon was with it´s 42,5 kg a little lighter and with 1710 mm also a little shorter as the MG 151/15. The bullets left the cannons barrel with 790 meters per second, at a cadence of 750 rounds per minute.
The weapon was "feeded" by an ammunition belt. One of these cartridges had a weight of 220 g, the projectile alone has a weight of 115 g.

So to sum it up

MGFF/M
-20mm
-1338 mm long (The actuall gun)
-26.3 Kg (This is the guns weight)
-540 RPM
-Projectile: 700 MPS
-Bullet weight: 220g
-Projectile weight: 115G

Mg151
-20mm
-1710 mm long (The actuall gun)
-750 RPM
-Projectile: 790 MPS
-Bullet Weight: 220g
-Projectile weight: 115g

The projectiles weight the same thing, the bullets are both 20mm, the Mg151 20mm is 20mmx82mm, the MgFF is 20mmx80mm (2mm difference), they have similar projectiles 700 MPS vs. 790 MPS.

So, my question is, why does the MgFF drop off so fast. It flys like a 30mm of a Mk108.

Thanks and

Karnak · « **Reply #1 on:** June 15, 2002, 11:22:08 PM »

MGFF/M
-20mm
-1338 mm long (The actuall gun)
-26.3 Kg (This is the guns weight)
-540 RPM
-Projectile: 700 MPS
-Bullet weight: 220g
-Projectile weight: 115G

Mg151
-20mm
-1710 mm long (The actuall gun)
-750 RPM
-Projectile: 790 MPS
-Bullet Weight: 220g
-Projectile weight: 115g

The MG151/20 has a barrel that is almost 40cm longer than the MG/FFM. This translates to a higher muzzle velocity (710m per second for the MG151/20 and 585m per second for the MG/FFM), which in turn translates into a flatter flight trajectory for the MG151/20.

Hooligan · « **Reply #2 on:** June 16, 2002, 12:54:34 AM »

The information I have indicates that projectile weights for the MGFF varied from about 90g to about 135g and muzzle velocities varied accordingly. Here are a couple of muzzle velocity/projectile weight pairs for the Mg151 and MGFF

MGFF
92g - 718m/s
115g - 585 m/s

Mg151
92g - 785 m/s
115g - 705 m/s

Differences in muzzle velocity translate to a big difference in drop. The problem is made worse because we are firing at targets which are moving away from us at a fairly high rate of speed. If a round fired at 800 m/s takes .6 seconds to catch a target, that same round fired at 700 m/s might take .9 seconds to catch the same target (for example), and this extra time of flight translates into significantly more drop.

Hooligan

Tony Williams · « **Reply #3 on:** June 16, 2002, 12:57:24 AM »

There are some errors in the quoted information.

The MG-FF/M fired two weights of projectile: 92g M-Geschoss at 700 m/s and 115g HE/T and API at 585 m/s.

The MG 151/20 fired the same projectiles at around 800 m/s and 710 m/s respectively.

The M-Geschoss were usually mixed in the belt with other types. However, as it was so light, the M-Geschoss lost velocity quickly and had a shorter maximum range.

Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Discussion forum at: http://forums.delphiforums.com/autogun/messages/

HoHun · « **Reply #4 on:** June 16, 2002, 03:16:56 AM »

Hi Hooligan,

>Differences in muzzle velocity translate to a big difference in drop.

Actually, the different muzzle velocities were carefully selected to compensate the difference in decelleration between the different rounds. Despite different muzzle velocities, projectile masses and ballistic coefficients, the actual trajectories of the rounds were very close at normal firing ranges.

Muzzle velocity was the projectile designers' means of matching dissimilar trajectories.

Regards,

Henning (HoHun)

Hooligan · « **Reply #5 on:** June 16, 2002, 09:11:30 AM »

HoHun I believe you misunderstood what I said. I was talking about the trajectory differences for similar projectiles fired from 2 different guns at differing muzzle velocities.

Hooligan

HoHun · « **Reply #6 on:** June 16, 2002, 12:08:38 PM »

Hi Hooligan,

>HoHun I believe you misunderstood what I said. I was talking about the trajectory differences for similar projectiles fired from 2 different guns at differing muzzle velocities.

Oops - I indeed thought you were talking about them being fired from the same gun. Sorry!

Regards,

Henning (HoHun)