Kramer Defense Introduces New 6.8x45mm UCC Round

Kramer Defense has released a new round for the AR-15 that they are calling the “6.8x45mm Urban Combat Cartridge”. The round is based on the 5.56mm case, necked up to .277″ caliber:

Las Vegas, Nev. – -( After four years of research and development, Kramer Defense announced the commercial release of the 6.8x45mm Urban Combat Cartridge (UCC) as a cost-effective, ballistically superior upgrade for the AR-15, M16, and M4 platforms.

The 6.8x45mm UCC provides military, law enforcement, and civilian users the ballistic performance similar to the 6.8mm Remington Special Purpose Cartridge in a package that is significantly more cost-effective and easily retrofitted to existing AR-15 patterned carbines.

Based on the 5.56 NATO cartridge case, the 6.8x45mm UCC offers a significant ballistic advantage over its parent cartridge and even outperforms the 7.62x39mm and the popular .300 AAC Blackout cartridges, when fired from similar barrel lengths.

The accompanying ballistics chart comparing these cartridges shows the advantage that the 6.8x45mm UCC provides the user.

6.8x45mm Urban Combat Cartridge UCC Ballistics Chart

6.8x45mm Urban Combat Cartridge UCC Ballistics Chart

The result of the company’s development work is a cartridge that offers AR-15 users the ultimate in flexibility. The 6.8x45mm UCC has proven to be ballistcally superior in short-barreled AR-15 carbines, cycles flawlessly in selective-fire weapons, handles projectiles suitable for hunting applications, and has performed extremely well in initial sound suppression tests.

“While we were focused on a solution for combat, the end result is probably the most efficient cartridge you can put in an AR-15,” said Larry Kramer, president of Kramer Defense.

“The 6.8x45mm UCC offers the best trade-off balance of increased terminal performance, cartridge size, projectile weight, velocity, weapon compatibility, magazine capacity and controllable recoil. It really is the ultimate intermediate caliber.”

Kramer Defense has loaded ammunition and complete AR-15 upper receivers for the 6.8x45mm UCC in stock and ready to ship.

6.8x45mm Urban Combat Cartridge UCC

6.8x45mm Urban Combat Cartridge UCC


Kramer Defense currently offers two commercial loadings for the 6.8x45mm UCC:

  • Standard Ammunition with 115 grain Nosler Open Tip Match (OTM) at 2,500 feet per second
  • Premium Ammunition with 110 grain Hornady Open Tip Match (OTM) at 2,500 feet per second 


    AR-15 Upper Receivers

    • Complete upper receivers available through Kramer Defense feature:
    • High pressure tested and magnetic particle inspected bolt
    • Premium Lothar Walther barrels made of LW19 chrome moly steel that are polygonally rifled, chromed lined and have a twist rate of 1:11.3

Longtime readers of my writing will know that I am skeptical of the utility of the new round. I’ve examined similar rounds to the new Kramer Defense offering previously. In 2014, I wrote a post where I designed a round similar to the 6.8×45 UCC to illustrate the numerous disadvantages that come from necking up the 5.56mm case, and earlier this year I wrote a post examining the surprisingly poor ballistics of the 6.8mm SPC, which is the ballistic superior of the new 6.8mm round.

For the new round, my skepticism extends to the chosen case length as well; the round appears to either be incompatible or to be poorly compatible with existing 6.8mm SPC projectiles, as its case is longer by approximately 2.2mm. Further, the ballistic chart published by Kramer does not appear to reflect actual ballistics in standard conditions. The stated retained energy of the 5.56x45mm round at 500m is, according to the chart, about 400 ft-lbs (542 J). This is an accurate figure for M855 when fired at 9,000 ft altitude, but is about 36% higher than the correct figure for sea level. The figures for the 6.8×45 and the other two rounds are likewise inflated. Another possibility is that the Kramer chart is mis-labeled; if the chart tracks energy in Joules and not ft-lbs, the figures used would be approximately accurate.

The round could prove useful for hunters living in states where calibers below .243″ are not allowed, if a sufficient supply of upper receivers and ammunition is made available, however.

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


  • Blake

    Sounds like a “case” of newcaliberitis. They would have had a much larger market & potential for success had they simply made ammo with these nice OTM bullets in an existing SAAMI standard cartridge with similar goals e.g. 6.5 Grendel.

    • 5.56 is fine. If you must have a bigger projectile, .300 Blackout exists and is plentiful. Just don’t have an ammo mixup.

      • AK™

        If you want a bigger projectile,use a .308Winchester/7.62x51mm.
        Bigger? .300Win Mag or .338 Lapua.

      • J E

        Would you ever consider liking a caliber other than 5.56×45?

        • NukeItFromOrbit

          I doubt it, the 6.8x43mm he maligns so much would still be an excellent substitute for 5.56x45mm as a military caliber. Admittedly it falls short of the illusive goal of also being able to replace 7.62x51mm.

          I know it doesn’t satisfy the ballistic gods of Mr. Nathaniel but thus far nobody has invented the perfect caliber.

          • How is a caliber that is heavier, has poorer ballistics, a lower fragmentation range, and breaks bolts faster an “excellent substitute” for 5.56?

            I don’t see how it’s some personal defect of mine that some companies have taken to hyping calibers that were improperly designed from the start. I am not someone who will equivocate just to make everyone happy.

          • NukeItFromOrbit

            Your second two points are debatable and the third isn’t true if the gun has been designed “right” versus conversions with absolutely minimal changes.

            For some cost in weight you’ve got something that hits harder out to 500 yards or so, within this range a majority of infantry combat occurs, at least in most conflicts.

            It’s nothing revolutionary nor it is some massive improvement but it is certainly a valid alternative to 5.56mm. Is there enough to suggest that current 5.56mm switch over to it? Not really. Yet if you weren’t concerned about per-existing stockpiles and standards there are good arguments for it, just as there are good arguments to be made for the 5.56mm.

            I’m sure you’ll argue how Mk.262 or some other match round offers better performance but Mk.262 doesn’t represent your standard issue cartridge. If your concern is just DMRs though, yes 5.56mm is a clear cut better choice as of today.

            Ultimately what most pleases the gods of ballistics is rather irrelevant to your average infantryman who would be hard pressed to hit anything beyond 400 yards in combat conditions with his standard rifle or carbine.

          • Please, tell me more about how a round that produces less velocity with lower BC bullets won’t perform more poorly from a ballistic standpoint, and will not have a shorter fragmentation range with equivalently constructed projectiles. Also, how does a round that produces more bolt thrust not wear out bolts faster? Are you saying that the correct configuration for a 6.8mm rifle is one based on the Remington R-15 with the .308-compatible bolt face? The vast majority of 6.8mm AR-15s that are made use the same old AR-15 bolt face that was originally designed for a 9.6mm case head at 52,000 PSI pressure, and the 6.8mm takes that up to a 10.8mm case head at 55,000 or even 58,000 PSI, a 37% increase in bolt thrust over the original .222 Remington for which the bolt was designed, and equivalent to a 5.56mm round that produces 71,100 PSI, over 3,000 PSI higher than the astronomically hot Mk. 262 round.

            This isn’t to say the round can’t be safely used in the AR-15, don’t get me wrong, but it will break bolts faster. Period.

            “Hits harder”. Larger-caliber fans like to use this term, but it doesn’t really mean anything, does it? Does the 6.8mm even produce more energy – which, remember, isn’t really as relevant as some would have you believe when determining lethality – per kilo than 5.56 with comparable bullets? No, it does not. In fact, it produces 6% less energy per pound at the muzzle, and that number only becomes less favorable as ranges increase.

            What you’re not considering is that 6.8mm SPC production loads don’t represent your standard issue cartridge either. The BTHPs available for it are all comparable to Mk. 262, and the alternative bullets that are not FMJs are not JAG approved. Further, a lead-free 6.8mm SPC projectile would reduce the performance of the 6.8mm round just as it does for 5.56, but the ability to increase pressure to make up the difference isn’t really an option for the 6.8mm, for the aforementioned bolt thrust reason.

            I will finally agree with you: Yes, what pleases the ballistics gods does not imply an increase in combat effectiveness. However, the inverse is not true. 6.8mm SPC is designed with no regard for ballistics whatsoever, and its performance suffers accordingly. This can be mitigated with better projectile design, but those projectile designs can be applied to 5.56mm as well, with equal or better results.

          • NukeItFromOrbit

            Yet those ballistics are good enough for the job of a standard infantry rifle or carbine. Hell, even the 7.62x39mm is arguably still good enough despite even worse ballistics.

            You only get the practical benefits of those superior ballistics once you hit a certain range. Generally speaking this will be about 500 yards if the 5.56mm and 6.8mm ammunition used are similar in terms of design and purpose. Up until that point the 6.8mm bullet is going to have more energy.

            Where do you get your information claiming that 6.8mm break bolts at a significantly higher rate than 5.56mm weapons? I wouldn’t be surprised if this were true earlier on, I’m sure the messed up 6.8mm specs early on caused all sorts of interesting failures. But what information are you going off of now to make that case?

            Regarding lethality, I’m far from an expert on the subject but I’ve heard so many contradictory things over the years that I’m unconvinced that there is any “primary” factor to it. Energy certainly factors into however and the more the better. Yes the 5.56mm is more efficient in regards to weight, but on a one for one basis the 6.8mm bullet is still going to have more energy behind it until it reaches that range discussed earlier. Efficiency isn’t everything.

            I’m not enough of a 6.8mm expert to argue on the issue of specific cartridges. Prod the 6.8mm fans enough and I’m sure some will debate you on that until hell freezes over but I’m not one of them.

            Ultimately I think what 6.8mm SPC started as is somewhat irrelevant to what it became and that isn’t a highly efficient long range performer. Yet even recognizing that it still has more energy behind it for a range that covers where a majority of infantry combat occurs. It isn’t more efficient about that energy, but brute force can go some ways it seems.

            I’m not arguing that 6.8mm is superior. Personally I put more value on velocity than most so I wouldn’t even call myself a fan. But to say it isn’t a valid alternative to 5.56mm for most uses would simply be false. There are reasons some might opt for it, especially for short barreled QCB carbines.

        • I like lots of calibers that aren’t 5.56mm, and some I like better than 5.56mm. The truth is just that 5.56mm isn’t so bad, and most calibers designed to usurp it are poorly designed.

      • Blake

        Agree. Heavier .224″ high-BC bullets with decent-length fast-twist bbls to accommodate them go a long way towards increasing the range & punch of the AR15.

  • Jeff

    Yet another rediscovery of what the Brits put forward in the late 40’s/early 50’s.

  • JCL

    I think 5.56x42mm made by necking down 6.8 spc case and combining it with longer 70 – 80 gr 5.56 bullet will make a better ammo.

    • MPWS

      Or even better: pulling back standard case to 43-42 mm and extending bullet length by same amount; perhaps the same you are proposing.
      Result – improved extended range ballistics with heavier bullet and minimum change to rifle; basically just removing barrel extension, cutting back barrel’s end by same amount and torqueing extension back.
      Chamber might be a miniscule tighter, true; but long term wear will look after that.
      This can be done with existing fleet for minimum expense. What will Nathanial say? “Not worth of effort”….. I know, he’s got buddies among latest upgrade team.

      • MPWS

        Actually, this is very similar to what Chinese did with their new ammunition. It as optimised performance versus weight and recoil. On top of it, cannot be used in either Russian nor American weapon. I do not see any reason to be enamored with 5.56×45.

        • JCL

          Someone in another firearm thread already experimenting with 5.56×42 bullet since 2008, and the result he posted show it can shoot 75gr bullet to 3000fps and 62gr bullet to 3400fps from 20″ barrel. The case pressure is between 55,000 – 58,000 psi which still lower than 5.56 NATO’s 62,000 psi. He also claimed the catridge shoot flatter than 6.5 grendel at 500 yards although i don’t know if this one’s true.

          • MPWS

            I believe it; what I do not believe to is those impossibly high (and unnecessary) velocities. With them the barrel wear is enormous and so is increased recoil force. Some 850-900 m/s is best compromise.

          • JCL

            Correct me if i’m wrong, but I always thought barrel wear is more the result of pressure rather than velocity of the bullet. Nevertheless, if fired from m4a1’s 14.5″ barrel the bullet will slow down to more reasonable speed.

          • JCL

            They also could reduce the powder or increase the bullet to 80gr, that might put the velocity to 2900 fps.

          • MPWS

            You are right, it comes as function of pressure and as you correctly stated, powder charge and bullet weight can be varied with particular objective. To me, lower speed and heavier bullet makes more sense than other way around.
            As a memory from time when I was employed in industry I recall seeing barrel slices in both 5.56 and 7.62; they look awful just after 2-3 k of rounds. Most of damage is by hot gas low erosion; 4-6 in ahead of chamber. Accelerating bullet finishes off the job by erasing lead strips.

          • JCL

            Does that mean an ak47 could last decades without barrel change because it has low velocity, low pressure catridge? What about ak74? Doesn’t 5.45 have about 880 m/s and about 55,000 psi can it last as long?

      • Not worth the effort.

  • Matrix3692

    I was just wondering, has anyone tried to fit a 8.5mm/.338 cal VLD bullet on a necked-up 5.56×45mm case?

    I always like the thought of a big, heavy, and high-BC subsonic bullet.

    • 8.6mm would mean a totally straight-walled case for 5.56, then where would you headspace from?

      • Matrix3692

        Maybe cut the case even shorter? i just need a subsonic round, so i suppose that would be fine?

        • Right, that would be a way to achieve adequate headspace, and all the .338-223 wildcats I’ve seen do that.

      • BrandonAKsALot

        Because no one has ever headspaced a straight walled cartridge before…..

        It would have to be from the case mouth like any other.

        • You can only do that if you don’t roll-crimp the case mouth, and if the brass is wide enough at the mouth, and I suspect it would not be.

          All the .338-223 wildcats I have seen cut the cases very short, I suspect so they could headspace off the thicker part of the brass.

          Keep in mind that most pistol cartridges substantially do not headspace off the case mouth in practice, the extractor just holds them in place.

          Not saying it couldn’t be done, but I suspect there’s a reason it’s not done very often. It probably doesn’t work particularly well due to the headspace problem.

    • PK

      .338 Whisper #2 from SSK Industries is a .221 Fireball necked up to .338. New barrel required, everything else stays the same for an AR-15.

  • jeff k

    more expensive ammo ? i am all for ammo development and making it better but if it only has 10% more power than a 7.62×39 and only 15% more than 300 blk than i dont see the point in cost to performance ratio imho

  • Alex Nicolin

    Great. A new round to blow up your .223 gun!

  • Cal S.

    These wildcat cartridges just keep coming. Tell you what, the first one that makes these things with prices comparable or lower to the 5.56NATO or .223 Rem is the one that gets my take.

    No? Ok, I’ll just skulk in the corner and smile through all the cash I’m saving.

  • Vitsaus

    I’m sure this one will totally take off, unlike the 500 previous proprietary AR15 cartridges that we have seen come out in the last 10-15 years.

  • Anonymoose

    I was wondering why no one ever did this. The idea seems like a good compromise between the Blackout and SPC.

  • nova3930

    Am I mistaken or is this a relabeling of the .277 Wolverine that’s been around a while now?

    • The .277 Wolverine’s case is shorter, but there was another wildcat being thrown around the 6.8 Forums and ARFCOM that I think was almost identical to Kramer’s offering.

  • Seburo

    Has anybody at TFB tried out .264 USA yet?

  • sam

    Oh those two words: “ballistically superior”. It’s metaphysically possible for that phrase to have useful meaning, but practically, that bridge has been burned.

    • 6.8 SPC has a higher MV and in some cases a better BC. It looks like Kramer is loading the 6.8×45 with the same 110gr BTHP bullets used in 6.8 SPC, but I’d be surprised if they were making magazine OAL with them.

      Oh god, I just defended the 6.8 a little bit. Now I feel dirty.

      • sam

        Yeah, that’s part of why I’m cynical about this new 6.8.

  • Avid Fan

    All it needs is a few billion dollars of development money and then it can be as marginally effective as .223. Hey win win for somebody.

  • Avid Fan

    So, seriously now. Using a 9.6mm case head, a maximum operating pressure of 62,000 psi, and a maximum length of 2.260 what could be developed?

  • TechnoTriticale

    Not prominent in this proposal is that it does require new magazines (which can also be used for 5.56, but not the converse).

    My understanding of the 6.8SPC development was that they wanted to use existing 5.56 mags, perhaps with new followers. The sidewall ribs impose inconvenient constraints (which in my view also led to the 300BLK being an interchange hazard).

    So this new wildcat is basically what the 6.8SPC would have been had they dropped the use-current-mags goal.

    • You’ve got it backwards. Yes, the 6.8 SPC was developed to use existing mags, but realistically that was wishful thinking; it was never going to successfully utilize 5.56 mags.

      The 6.8×45 is based off the 5.56 case, and is at least advertised as using existing magazines, though I couldn’t tell you how successfully it does so.

      • TechnoTriticale

        re: The 6.8×45 is based off the 5.56 case, and is at least advertised as using existing magazines …

        Got a link or quote for that? I infer the opposite from their site:
        Laying the groundwork for it, when discussing 6.8SPC, they say:
        “Replacing magazines is not a big issue as they are considered an expendable item and are replaced constantly.”

        In features & benefits, they say:
        “6.8 x 45-mm UCC magazines will still function with 5.56 NATO, if needed”
        but silence on the reverse, and …

        They sell 6.8×45-specific mags & modified Magpuls. Why would those be needed?

        I read it all as:
        • You need new mags for 6.8×45.
        • You can use these mags with 5.56.
        • You can’t use 5.56 mags with 6.8×45.

        • Ahah, you’re right, I must have been misremembering. Sounds like a similar situation to the 7.62×40 WT. The shoulder is too far forward and neck is too wide to work with 5.56 mags.

  • Phil Elliott

    Been shooting a 7mm TCU (.280x45mm) for years, granted my bbl. is only 10″. Still only a 200 yd. Deer gun. Don’t know how it would do with an 18″ bbl.

  • NDS

    Who shoots 300BLK through a 16″ barrel?

  • jjpaul

    Lmao why is everyone so emotionally fragile about caliber? So what if Nathaniel likes 5.56.

    • NukeItFromOrbit

      Say what you want about me mum, just don’t talk bad about my choice in caliber.

  • StickShift

    Is there any reason why a 5.56x45mm case necked up to 6mm hasn’t become popular yet?

    • NukeItFromOrbit

      Both the 6x45mm and 6.5x42mm looked pretty good to me. Could use the same magazines fine too.

  • Robert Griffith

    How does this round compare to the 25-45 Sharps? Will it fit and function in standard AR mags or are special mags required?