I was always under the impression that the Robocop gun was a modified long-slide 93R...I never really did any research on it though, it just looked like it to me. Is that a common misconception?
According to the article on the
The RoboCop Archive, it was a standard M93R, with custom-made barrel extension with compensator, modified rear sight and a larger grip to fit Robo's hand. Here's part of the article:
But the really big advantage of this particular Baretta was that it fires a three-shot burst every time you pull the trigger. So what that gave the filmmakers was a very large quantity of flame, all in one burst. To maximize that effect, vents were cut into the barrel giving it a flame direction off to the side. This increased the overall look from different angles and gave it a little more flash. Sometimes they got a flame out the side ten inches long and another flame out the front over a foot long.
Admittedly, a nice gun.
On Calicos: in
RoboCop 3, the "Rocket Scientist" robbing the Donut shop has one of those Calico rifles, and the pistol makes up the machinegun on Robo's Gunarm, but it looks like they added another helical mag to look like the flamethower fuel tanks (I am so sad for noticing this).
In the B-movie
Space Marines, The Marines use Calico rifles, where the bad guys use an assortment of AKs, and in one case, an M203 with a custom pistol grip.
Other guns: A few of the guns in
Doom are built around G-36 rifles.
The Marine guns in
Wing Commander are AK47 rifles with the buttstock removed and an attached GP-30.
The
Judge Dredd Lawgivers were Beretta 92Fs converted to full-auto by the armourers, and the Judge Hunter rifles were based on AK-47 rifles.
The ZF-1 from
The Fifth Element was an AKS-74U.
That's about the limit of my gun-geek potential.
Detailed responses from my THR friends not afraid to look nerdier than I to follow. 
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