9-part custom bombs on a durable rack optimized for low-physics mode. Also includes Boom25 & 50 versions of 'M117,' as well as Boom 50-Mk82.
Has jettison feature that doesn't use any AGs. Main M117 bombs are a loose replica of M117 GP bombs with basic tail fins.

Impact effect (medium graphics)

Bombs on an F-112A1 Awoogar fighter bomber (has older version of MBR, not included in this set)

Performance cost of the whole assembly: 38.7
(not including the top pylon)
Performance cost per bomb: 35.7
(PC of normal Boom50 is 17.6)

Jettison Feature

Simply enable Air to Air mode and select a weapons named "Jettison Bomb." Doesn't work with Boom 25/50 version of M117.
(uses a disabled cannon inside the pylon part, you can remove it and save some performance cost if you don't need this feature. I put it in air to air mode since the Air to Ground mode of my planes tend to get cluttered with other weapons.)

Safety

Fly at least 350 meters high from the ground you are dropping the bombs on.

Specifications

M117
-348kg / 9 parts each
-Explosion scale 3.2
-Diameter 408mm
-1/1 scale loose replica.
*Version 1.17

Boom50 Mk82
-The black pylon one.
-Dimensions should be close to the real thing.

*Check out ThomasRoderick's "Somewhat more Accurate Ordnance Sizes and old flight models" pack (link) for more rescaled weapons. (Bombs in my M117 pack are not from his post.)

Multiple Bomb Rack/MBR (v1.4)
-13parts + 1 (long pylon) each
-358kg
-Recommended max load 2,100kg
-Built for low physics mode.
Not a replica, but dimensions and station positions are largely based on MER schematics (I think it was BRU-41) and thus should be pretty close to the real thing. Took me some time to find the figure for total length (which was of MER, but they should be close). Your aircraft/pylon must be strengthened to prevent wobble/vibration.
To use jettison all feature, save the yellow cannon with the MBR, and attach it somewhere on your plane. It works just like the jettison bomb feature. Alternatively, you can simply assign an activation group to your pylon.

M117
Older general purpose bombs used on US aircrafts. Built for my 1950-70 era fighter bomber. Didn't intend to include Boom25 and 50 vers at first, but did so just to be thorough. It was a pain, and honestly a waste of time. (Ha, ha, ha...)

MBR
Initially this was a simple fuselage block with no actual weapon stations, but I decided to make it more elaborate as I wanted this to be an actually useful sub-assembly that can be used to hold other bombs as well... but that plan kind of ended up not-realized as I couldn't solve the mass/strength (and wobble) problem of low-physics mode without massively increasing the overall weight of the assembly. If I wanted to be able to simply attach M117 and other heavy bombs to the pylons and not have them vibrate like crazy, I had to up their mass by more than 10, which would've resulted in insanely heavy bomb rack. Unfortunately, the final version is heavy as it is at 360kg (I think the real MER is about 90kgs... if my memory is correct), and it kinda resulted in a half-baked, not very satisfactory end product. At least it can carry Mk82 and Mk81s on pylons, so that's a tiny saving grace.
During my research phase, I stumbled upon a page about the development history of the actual MBR (which was the basis of later MER and TER (triple ejector rack)). If you are interested in history of these equipments, I'd definitely recommend you check it out.
http://www.skyhawk.org/article/mcbr-fitch