Modern Personal Defense Weapon Calibers 005: The 5.56x30mm MARS

Left to right: the 5.56x30mm MARS, 5.56 MARS tracer, 10mm MARS, 5.56x45mm M193

Today on Modern PDW Calibers we’re going to look at what might seem like a humdrum round, but which represents an important performance band for the modern personal defense weapon. That round is the 5.56x30mm MARS, a purpose built “micro assault rifle” cartridge from Colt designed to fill a similar niche to the WWII-era .30 M1 Carbine.

We’ve mentioned the MARS and its short 5.56mm round before,┬áin a rebuttal to a piece from Business Insider. Designed in the late 1990s as part of a Colt project for what was essentially a spiritual successor to the M1 Carbine, the 5.56x30mm MARS represents a take on the Personal Defense Weapon caliber that is rarely explored. Too large for use in handguns, but much smaller and less powerful than intermediate assault rifle rounds, the 5.56x30mm is a sort of “everything you need and nothing you don’t” round for echelon troops, special forces, and other units requiring a small, maneuverable weapon with a potent but moderate round. With a muzzle velocity of approximately 2,600 ft/s (800 m/s) with a 55gr (3.6g) bullet, the 5.56×30 MARS is a sort of “small caliber, medium velocity” (SCMV) round that could give all the benefits of a rifle at close ranges with almost all the benefits of a submachine gun, including ammunition tailor-made for short, 10.5″ barrels.

The 5.56x30mm MARS is similar to many other rounds, including the .221 Fireball (center), .22 Aberdeen Proving Grounds Carbine (middle right), and .22 Johnson Spitfire (far right).


Before we get into the ballistics, I should make a note about the figures I am using for the 5.56mm MARS and for the 5.56 M193. There is quite a lot of variety in the shapes of different 55gr “M193” bullets, even within one lot, and this leads to substantial differences in the ballistic coefficients of each individual bullet. 0.120 G7 is an accepted value for the ballistic coefficient of M193, but it represents the blunter, less aerodynamic bullet shapes that can be found in ammunition labeled “M193”. Other projectiles of the same weight, such as the Sierra 55gr FMJ, may have much higher ballistic coefficients in the 0.140-0.150 range, due to their finer shape. For the 5.56mm M193, I have used the 0.120 G7 figure to represent what is generally accepted to be the performance of this round, but I have used a higher 0.145 G7 BC figure for the 5.56mm MARS, as the MARS rounds in my possession have what appear to be loaded with bullets on the finer end.

Anyway, onto the charts:

In many respects, the 5.56×30 MARS was nothing new, even when it was first developed. The .221 Remington Fireball preceded it, and even the very first modern SCHV round – the .22 Gustafson/Aberdeen Proving Ground Carbine round – closely resembles it. In the 1980s, the French also developed a similar round, the 5.56×30 GIAT. However, the 5.56×30 MARS is perhaps the most refined, and therefore makes a good representative of this class of rounds. The MARS was designed specifically to have the most efficient ignition and highest possible performance from short barrels, and came packaged with a quite handy looking shortened AR-15-style carbine to match. Since the 5.56 MARS was developed, the Indians have also played around with a very similar round, the 5.56x30mm MINSAS.

What sets the 5.56×30 MARS and similar calibers apart from rounds like the 5.7×28 FN is that they are designed specifically for use in carbines and micro assault rifles, and not with any provision for use in pistols, and that they are higher performance than most high velocity rounds designed for handgun use but less powerful than traditional SCHV rounds like 5.56x45mm.

In terms of weight, the 5.56x30mm MARS is a bit lighter then 5.56mm as you might expect, with my samples all weighing between 9.6 and 9.9 grams.

Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at


  • Henry C.

    Is there any information available on that 10mm MARS round?

  • lostintranslation

    If there is no advantage at close quarters (Mil), against body armour, is this a solution seeking a problem?

    • ostiariusalpha

      I believe this would easily penetrate a CRISAT target, which was equivalent to the type of body armor worn by Soviet soldiers in the 70’s and 80’s.

    • RSG

      Without a steel core penetrator, all these bullets would require hitting around 3200fps to pass through level 3. The M193 out of the 20″ barrel does so reliably.

      • lostintranslation

        Shock with the first round then; Urgent Operational Requirements (UOR) for billie jack, sap or slapper.

  • roguetechie

    I’ve always wanted to experiment with the 9mm MARS case and cbj ms sabot encased 5.56 bullets to see just how far you could push this.

  • John Dyer

    Wouldn’t 5.56×30 have the advantage of also having less flash and/or concussion? Or can a 5.56×45 out of a 10.5 barrel have a similar flash/sound signature? Obviously long barrel/5.56×45 is better than SBR/5.56×30, ballistically. However as an alternative to a sub gun perhaps this has merit?

    Also would seem more cost effective than the rest of the modern small rifle-cartridge-style PDW calibers? Reuse barrels and bullets and bolts (but need a new chamber)

    • Tom

      A round that is loaded specifically for a given barrel length will perform better in terms of muzzle blast. Also such a rifle can be shorter and lighter.

      The question however remains is the added cost and complexity in the supply chain worth it for a small weight saving over the M4? If a soldier cannot carry an M4 is he really going to be able to carry a ‘mini assault rifle’ of will he just stick with a pistol? Is less bang and flash when firing worth loosing ammunition compatibility with everyone else toting 5.56mm NATO weapons.

      • You’ve hit on the real issue with cartridges like the MARS and 6×35 KAC, which is that while extremely cool, they offer “too much of a good thing” in terms of performance, and you end up with a “PDW” that is barely shorter or lighter then the 5.56 weapon it was designed to supplement.

        In the case of the Colt MARS rifle, it’s specced at:
        -23.5″ collapsed / 27.7″ stock extended
        -5.4lbs empty / 6.2lbs loaded w/ iron sights.

        So it’s pretty hard to see a case where this would be carried in the place of a pistol, or chosen instead of a 5.56 10″ barrel.

        However, for civilian home defense use or for LEO’s grabbing a rifle out of a Squad car, it would have been a dandy little rifle.

        • demophilus

          FWIW, I seem to recall seeing a picture of the MARS in a holster. Doesn’t mean it was practical, but there it is.

          According to Small Arms Review, the Israeli police were considering the MARS as an Uzi replacement, but they only wanted 20,000 units, and tooling up didn’t pencil out. And, Colt didn’t want to cannibalize its M-16 orders.

          Me, I sort of wonder what might have happened if Aberdeen kept developing the .22 APG. A non-proprietary drop-in replacement for .30 Carbine might have been interesting.

          • I personally love the whole field of PDW’s, I think they’re a very interesting / neat class of blasters.

            Having reviewed most of them, I’m of the opinion that for a PDW to really succeed in its role of handgun/rifle replacement for support troops, it has to be holsterable, which means that the PDW cartridge has to be able to fit into the grip of the weapon.

            This would exclude the M1 carbine, Colt Mars, KAC PDW, Krinkov, MPX PDW, and P90.

            Of what is out there, that leaves the MP7, PP-2000, and B&T MP9, with the MP9 being the ideal in terms of size and weight (12″ folded, 3lbs weight.)

            Cartridge wise, the easiest solution would be an AP 9mm / JHP 9mm combo. The other would be a MP9 in 5.7×28 that uses Five-seveN magazines, firing a hotter, 31gr version of the M855A1 EPR projectile at 2,200-2,300fps.

            The best option though might be something like a MP9 firing the 7.5 FK cartridge, or something a bit weaker (so that it could be fired in a Glock size pistol with controllable recoil) such as a 7.62×25 +p+ firing a 70gr EPR projectile at 2,000fps / 622 ftlbs. That would make for a pretty interesting 9mm replacement.

          • William Elliott

            Don’t forget the B&T USW…had a crazy thought, cross the BRNO 7.5 FK pistol with the USW…Naaaah, too crazy…

          • More like just the right amount of crazy! Possibly with a spring loaded folding foregrip that deploys as the weapon is removed from the holster?