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 Post Posted: Sun Sep 11, 2011 1:26 am 
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I was looking at the AK-47 article in wikipedia in spanish and I was surprised that the gun has a drum cartridge. When I wnet looking for an image, I half expected to find the cartrigde on top of the rifle a la Zaku II. However it was hanging from the gun, in front of the trigger.

This got me thinking if the Zaku II rifle is feasible, I mean how does the bullets get down to the cannon?

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 Post Posted: Sun Sep 11, 2011 1:43 am 
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There are real-world examples of guns with top-mounted circular drums, like the Soviet Detgyaryov MG and American Lewis gun, for starters. That makes it pretty clear that such drums are indeed plausible, though I don't know enough about gun mechanics to explain how such a design works. I also don't know if any Gundam supplementary publication tries to describe the workings of the Zaku MG.

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 Post Posted: Sun Sep 11, 2011 1:59 am 
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In essence, each new round falls down into the chamber from above, rather than being pushed up from below, as with more traditional mounts for detachable magazines. Note that the regular GM 90mm machine gun also features a top-loading magazine...and in a bullpup style, no less. These are both perfectly workable systems.

Now, if you want to talk about the idea of having a 120mm firearm perched 12-15 meters off the ground and using fully automatic fire...that's a different kettle of fish for "feasibility".


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 Post Posted: Sun Sep 11, 2011 1:04 pm 
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Thank you people.
@ Black knight. What is a bullpup style rifle? And could you please elaborate on the feasibility of automatic fire 15 meters above the floor. Is this type of weapon not suited for mecha usage? I thought it should do fine since at the basic, mobile suits are scaled up infantry soldiers.

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 Post Posted: Sun Sep 11, 2011 1:50 pm 
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A "bullpup" machinegun is a weapon that has the magazine behind the trigger assembly rather than in front like a conventional machinegun. The result is that you get a shorter overall length for the same barrel length. For example, the Steyr AUG is a bullpup rifle with the same barrel length as the M16, but the actual weapon is significantly shorter.

The GM's 90mm machine gun is a bullpup machinegun.

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 Post Posted: Sun Sep 11, 2011 2:21 pm 
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nacho-wan wrote:
@ Black knight. What is a bullpup style rifle? And could you please elaborate on the feasibility of automatic fire 15 meters above the floor. Is this type of weapon not suited for mecha usage? I thought it should do fine since at the basic, mobile suits are scaled up infantry soldiers.

Dark Duel has handled the "What is a bullpup?" so I'll go in for the other.

It comes down to the concept of center of mass. Mobile suits are tall, and don't weigh very much for their volume. So they have fairly high centers of mass. What's the big deal about center of mass? It determines how stable a platform the machine is when acted upon by another force. How likely the object/machine/whatever is to fall over, for example. What's the easiest way to knock over a chair, pushing with a rapid horizontal force against the top, the middle (say, where the seat is) or against the legs just inches from the floor? The top, clearly.

Now, you're firing a big 120mm weapon. It's going to have some nasty recoil. Which makes a better firing platform, holding it 15 meters off the ground in the hands of a 60-ton mecha, or putting it 1.5 meters off the ground in the bowels of a 60-ton tank? The tank is clearly going to handle the recoil better -- for one thing, firing it is unlikely to knock the tank over, because the tank has a greatly lower center of mass. Even firing a medium-powered rifle like the M16 family while standing leads to poor accuracy; there's a reason snipers don't shoot from the standing position, but rather from the prone, and it's not all about survivability.

If your Zaku 120mm MG is firing shots equal in power to modern 120mm tank guns (and the shell casings that Amuro dodges look about the same size) then it should suffer from pretty bad recoil issues, especially on full automatic. Even the M16/M4 family suffer from poor accuracy on full auto, and 5.56mm is a fairly wimpy "assault rifle" round. If your 120mm Zaku MG is not firing a fully automatic Main Battle Tank weapon, but more a sub-machine gun style in 120mm, then much of the complaint goes away (though MS are still far too light for their volume and demonstrated armor strength), but so does most of the power. If 120mm MGs are really 120mm SMGs, then a Zaku MG should have very little chance of penetrating the frontal armor of a Type-61 tank. Here the height comes into advantage, as at close ranges the Zaku MG could penetrate the doubtless-thin top armor of the Type-61, but the 150mm cannon of the Type-61 should have no difficulty penetrating Zaku armor at any range, giving the tanks a distinct advantage in open-field combat, such as in deserts or the central European plain.


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 Post Posted: Sun Sep 11, 2011 7:21 pm 
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Of course, there is the possibility that the Zaku's 120mm ammunition isn't the same as a tank's, but that's doubtful since MSs are suppose to be walking tanks... Think of it as the difference between a .50 BMG (or 12.7x99mm NATO) and a .50 AE (12.7x33mm).

Anyways, this is what the M1A1 Abrams's L44 120mm gun looks like firing: http://www.youtube.com/watch?v=M9O3KDGO3Wk

Now imagine something like that being fired by a 18m walking robot at full-auto.

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 Post Posted: Sun Sep 11, 2011 8:21 pm 
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I think the recoil problem of MS is best demonstrated using the Zaku Cannon as an example. In the last part of its profile, you can read a fragment of its original background indicating that the recoil problems cuased by its 180mm back mounted cannon were so bad that it led to the project's cancellation. This explanation came along with the original indication that only 9 Zaku Cannons were manufactured, but today it's commonly accepted that more had to be produced, mainly considering videogames, but also canon sources such as the 08th team OVA and the Z tv series.

I do should point out that the 08th team actually seemed to consider the recoil problems more realistically as the unit depicted is laying on the ground rather than standing up.


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 Post Posted: Sun Sep 11, 2011 8:48 pm 
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Sure, you can see recoil actually being considered as early as MSG, when Amuro launches in Guncannon rather than Gundam against Ramba Ral & friends, and crouches down on all four limbs, lowering the center of mass and providing a far more stable firing platform for the cannons.


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 Post Posted: Sun Sep 11, 2011 10:09 pm 
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if we take the fact the zaku II had AMBAC the backpack thrusters may activate to hold the zaku up also we see the zaku's taking a firing stance the Zaku seems to have the ability to switch from full auto to semi fire. the Zaku Cannons we see in 08th ms team got around the issue of not being able to stand and fire by basically converting Zaku II units in to artillery emplacements. I would think that the real issue with running it at full auto would be wasting fuel and ammo running it that way all of the time.

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 Post Posted: Mon Sep 12, 2011 10:28 am 
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What does AMBAC have to do with the thrusters? Last I checked AMBAC was simply moving the limbs of the MS while not using the thrusters so they could save some fuel.

Personally I think that the 120mm cartridges used by the Zaku are weaker in comparison to a modern 120mm tank round. In 08th MS team when Shiro shot the drum for Topp's machine gun with a rocket you could see some of the cartridges. They look very stubby to me compared to a modern tank cartridge like that of a large pistol cartridge.

Now I don't know how accurate the art is for them in 08th MS team but, IIRC the casings also look like giant pistol casings in the original series as well, it would help explain how they can store 100 shots in a drum that isn't really that much larger in comparison to the normal machine gun magazines, which have much lower capacities, used by MS.

120mm cartridges from 08th MS team:
http://i19.photobucket.com/albums/b185/ ... LE0454.jpg

GM rifle picture that shows a cartridge for a comparison:
http://i19.photobucket.com/albums/b185/ ... mrifle.jpg

Now if you compare the 120mm cartridges in that picture to a 120mm tank round you can see that they appear to be shorter while the 90mm cartridge for the GM rifle looks like it is of similar length and possibly design. Now for me that makes me think the 120mm is more of a giant sub machine gun (as in it uses what are basically giant pistol cartridges) than a rifle or machine gun, while the GM rifle, and based on the magazine shape and size the more common 90mm Fed bullpup, are more like giant rifles or at least fire what are basically giant rifle cartridges. That is based on what I can see in cartridges design however and I obviously have no idea how wrong or correct that is.

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 Post Posted: Mon Sep 12, 2011 5:56 pm 
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Well we know that later in the war Zeon switched to using weapons with a lower caliber and a higher muzzle velocity so its not that far fetched to assume that the 120mm round used in the MGs is smaller that a modern tank round and therefore has a lower muzzle velocity.

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 Post Posted: Mon Sep 12, 2011 6:36 pm 
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RGM-79 GM:

The PG and MG Ver. 2.0 model kits of the Zaku both include a detailed version of their Zaku machinegun, down to the drum which can be opened and where you can see exactly how large a catridge is.

-In the PG kit, check the left image at the bottom of the page.

-In the MG kit, check the image right above the "Box Art" heading.

I hope you find this useful.


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 Post Posted: Mon Sep 12, 2011 9:37 pm 
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Thanks for showing me those but I'm still not entirely convinced either way. I mean the line art for the 120mm machine gun has a very small ejector port which means it would need a small casing. So I don't know what would be considered more accurate. The 08th MS animation and MSG line art or the model kits. *shrugs* I guess it could just be up to whoever makes/draws the particular thing.

http://i19.photobucket.com/albums/b185/ ... inegun.jpg

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 Post Posted: Mon Sep 12, 2011 10:09 pm 
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For what it's worth, while the lineart from MSG shows it ejecting to the left, and we see this in the first episode of MSG, I noticed that the later versions seen in 08th MS Team and 0083 don't show the ejector port. While I don't recall either series ever showing us a clear shot of shells ejecting to the right, if you go back to episode 8 of 08th MS Team to just before Shiro shoots the Zaku's gun in the pic you posted before, it looks as if the weapon has the port on the right, and it looks similarly small to the one in the lineart from MSG. Of course, if you look at the Hizack's machine gun, which is supposed to fire the same exact shell as those others, it's port is back on the left, and looks a bit larger than the others...

So, as you said, it's probably just up to the person who drew the art for the series in question. :roll:

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 Post Posted: Tue Sep 13, 2011 3:27 pm 
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That makes sense I suppose. Most movies/shows have things change based on the design or art people. Gundam isn't really known for great design consistency or technical design accuracy to begin with. Or it could just be that originally it was going to be a small cartridge and then they decided to make it larger but considering 08th MS team has them small and then the Hizack has it longer it is most likely that the designer picks it.

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 Post Posted: Tue Sep 13, 2011 4:52 pm 
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Well the Zeta era version of the gun is desgined to resemble the 0079 art the later line art used for 08th ms team tried to make the 1979 style line art look more realistic.

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 Post Posted: Tue Sep 13, 2011 8:59 pm 
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The Pan style magazine is- shall we say, an overly complicated feed system, but it certainly worked in it's day.
Here's a picture of the Lewis Gun magazine

The cartridges are aligned with the bullet facing the center of the drum, the pan rotates with each repetition and the bolt strips the cartridge from the feed lip.

This was before the disintegrating-link style belt was common, and period (early-1900's) box magazines were problematic with rimmed cartridges like the British .303 and Russian 7.62x54R. The Lewis gun was very reliable in WWI compared to the other "Light" machine guns, namely the French Chauchat. That said, by World War II- magazine and belt feed designs on light machine guns and self loading rifles had really been figured out. There is no reason for a Pan style magazine now, except because thats how they drew it! Also note that in 0083, the African Remnants F2's used a box magazine loaded with Flak type ammo, so the design isn't limited to the pan mag.

It's still true that in any autoloading firearm, the magazine is the weakest link.

In terms of recoil system, the gun has been drawn with a moving barrel, ie- the fore-end remains stationary and the barrel recoils within it (See the Zaku's tearing up Side 7 in MSG, If I remember right the whole barrel recoiled.) this makes me feel the action is similar to the Browning Short Recoil system, found in various pistols, shotguns, and machine guns, it would fire from a closed, locked bolt, the barrel would then recoil WITH the bolt for a short span before the gun unlocked and the bolt stripped the fired case from the chamber. Considering this action is used in the .50 M2 machine gun, it should do a excellent job scaled up to mobile suit size.

I really feel the cartridge, if we weren't just arbitrarily assigning sizes to things, should be more in the range of 60mm to 76mm if it were to maintain a traditional 'necked' rifle style cartridge. HOWEVER it could be a large volume, low pressure case design like say .30 Carbine or more accurately .458 SOCOM- Big case, gigantic bullet, not moving that fast. This would also explain the MMP80 supplementing the MMP78, perhaps it's smaller 90mm cartridge was zippier than the 120mm with a higher case pressure. Or just cheaper to make. Or if it were a rifle style cartridge- perhaps the 90mm came along because the 120 was TOO stout and was damaging the MMP78's?

I like to see the 90mm cartridge in the MMP80 and perhaps the GM "Cold District" type SMG as an allegory for our man sized 9x19mm Parabellum. In that case you could consider the 120 as something more like my favorite cartridge, the .45ACP. 9mm ball penetrates much better than .45 ball and the recoil is lower but snappier. This doesn't account for how wide the pan magazine is though.


EDITED TO ADD- I'm still trying to figure out how the magazine works on the 100mm Ground type machine gun, and what the cartridge might look like. It's not as clear to me as the MMP78.

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 Post Posted: Thu Oct 13, 2011 7:35 pm 
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Well Igloo Ep 2 has a scene where a few rounds from a Zakus 120mm spills out.

Their a lot longer than the 08th ones.

If anything if my 1/144 scale Zaku II is anything to go by then the ammo drum is around 7.5 feet in diameter (~2.3m), current day 120mm ammo is about 1,000mm in length. So it's possible they are full sized AP rounds, though of what type I'm not sure, the animation I believe seems to indicate full caliber rounds.

Though one interesting question is IIRC the 90mm MGs where said to be better for anti mobile suit use, even though in theory the 120mm is a more powerful round, and carry's a larger mag (100 rd vs ~32).

Though one oddity is at 100 rounds your looking at around 2.5-3.0 metric tons per mag (including the weight of the mag, which would need a feed system as gravity is not going to help you in space...).

From what Igloo indicates the the mobile suit scale Autocannons (both the GMs and Zakus) seem to fire at around 600 RPM (roughly 30 frames per second and a mussel flash was seen every three frames, at lest when I looked at it), though it also has GMs firing sustained bursts of around five seconds in length with their 90mm guns (that only hold 20 rounds... :roll: ).


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 Post Posted: Fri Oct 14, 2011 6:14 am 
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Fall_Ryan wrote:
EDITED TO ADD- I'm still trying to figure out how the magazine works on the 100mm Ground type machine gun, and what the cartridge might look like. It's not as clear to me as the MMP78.

Well according to the MG manual the magazine "slides" into/onto the machine gun horizontally but maybe that's just a mechanic of the model? The MSiA version "pegs" in. I'm not really sure how it would feed though or even that it could hold a respectable amount of ammunition.

http://dalong.net/review/mg/m40/p/m40_m0009.jpg
http://dalong.net/review/mg/m96/p/m96_mb0019.JPG
http://dalong.net/review/mg/m96/p/m96_mb0018.JPG

You can see a really small round toward the bottom of the first scan. Looks like more of a rifle casing than a pistol one I guess? Certainly doesn't look like a scaled up 10mm round from a Colt Delta Force Elite :twisted:

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