Looking To Finally Do A Mk 18 SBR...

[SteyrAUG]

I have plenty of SBRs such as the Colt 6933, Bushmaster Entry and a few others, but they are all original configuration.

Even though I have fortified the Bushmaster, I still don't have 100% faith in it as a "all the marbles" defensive weapon despite that fact that it's been 100% reliable so far.

I like the Colt 6933 for what it is, a super light SBR without a ton of crap on it. I also worry the lightweight barrel may not be the best barrel for regular suppressor use.

So I'm looking at the DD Mk18 10" SBR as a base rifle and starting point. This will give me a factory SBR of acceptable quality with a full rail system in place. I always thought going below 11.5" was some kind of "point of no return" as far as performance but have heard plenty of good things about the DD 10" and 10.3" rifles.

Please correct me if I'm wrong. I'd go with a DD 11.5" SBR but none of my suppliers seem to offer them and 10" or 10.5" seem to be a defining criteria for a Mk18 type SBR.

Also need to know what is the best suppressor for a DD Mk18 10" barrel that will not be too heavy and will clear the rail system. I'm looking at SureFire suppressors but haven't determined which one would be best for my needs. Did several searches and their seems to be a lot of divergent opinions on the best suppressor for this rifle.

After that I just know I need a weapon light, BUIS and a RDS which should be the easy part.

So what am I missing? What do I need to know?

[kaltesherz]

Why don't you just pick up one of the new 11.5 BCM KMR uppers and throw it on that Bushmaster lower?

I plan on picking up a 5.56 Saker in the near future to run on mine (once my Form 1 clears). It's extremely durable, quiet, and has a bunch of innovative features. Plus it's a bit cheaper than Surefire.

[Col_Crocs]

^this. You seem to already lean towards an 11.5 anyway. That plus, it should be a lighter set up overall.

[kwilkin]

Personally, my view is that the only thing "Mk18" on the DD offerings is the rail system.* Now that that's out of the way....

Overall, I thing you would be better served with a Colt, BCM, or LMT SBR upper. The DD 10.3" barrel is now well-understood to be over-gassed for NATO-spec ammo. The gas port has been shown to be nearly .1" larger than spec. DD does this so that their guns will cycle with a wider range of commercial ammo. Shooting hotter loads in an over-gassed system will put additional stress on other components critical to smooth operation of the system. This means more regular maintenance/replacement of parts and the potential for unexpected failures. Add a suppressor on there, and the problem is exacerbated. This is not to say that there aren't many satisfied users of DD uppers.

If you want a very close clone of an issued Mk18, I suggest picking up either a complete upper or just a MK18BA (barrel assembly) from Specialized Armament Warehouse. These are all Colt Defense parts and will be closer to spec. The downside is obviously cost.

The LMT 10.5" upper is a good starting point for a Mk18 clone. The barrel is 10.5" instead of 10.3" but they will have a more appropriately sized gas port. Another advantage is that LMT 10.5" barrels have a slightly heavier contour under the handguards which adds additional rigidity while having a suppressor mounted which, in theory, should reduce POA/POI issues with a suppressor mounted.

Both the LMT and SAW MK18BA assemblies will require you to remove the front sight base and install a Mk12/Crane-style/low-profile gas block to install the RIS II rail, so that is something to consider. Also, DD has temporarily suspended commercial sales of the RIS II rails (FDE) while they fulfill a military contract. So, the only way you are going to find that rail is on their complete uppers or rifles. I'm sure they will offer them again, no one knows when that will be, however.

SureFire SOCOM and KAC NT4-QDSS suppressors are correct (i.e., issued) for the M4/M4A1/Mk18/CQBR and will both be suitable/warrantied for use on 10.3" barrels and will clear the rail. AAC suppressors, as is my understanding, need additional clearance on a 10.3" barrel with the RIS II, so a 10.5" barrel is recommended for those. I'm not sure about other suppressors as I'm a clone guy and try to stick to spec.

There is some debate about the optimal SBR length. Some people like to go short as possible, while there is evidence that supports 11.5" as a more optimal length. So, you have to balance how accurate you want to be with parts availability, cost, and which suppressor you plan to use.

*Note also that the "Mk18" is a specific military designation for a particular type of weapon. What DD is offering is actually a clone of M4A1 Block II CQBR (close quarters battle receiver). DD has, in my opinion, hijacked these military designations for marketing purposes to sell to the uninitiated. For example, their "Mk12" is anything but with the exception of 18" barrel profiled for an Ops-Inc suppressor and, like the "Mk18," their M4A1 doesn't have the proper RO921HB-profile barrel. I feel compelled to point this out, although most people don't seem to care about such issues.

[scooter22]

Although I do want a factory DD Mk18, I am under the impression that they may be slightly over-gassed.

However, this can obviously be amended by the use of an adjustable gas block.

If you haven't already, check out Grant's thread: "Best Suppressed SBR Ever?" https://www.m4carbine.net/showthread...essed-SBR-Ever

I found this thread very helpful in deciding on which SBR set-up to go with next (BCM 11.5" + Syrac adjustable block).

FWIW, I chose the SF SOCOM556-RC based on SF's reputation and solid mounting system.

[domestique]

Do you want a MK18 for the clone value and/or do you need all the rail space?

I personally would look elsewhere for a 10.3-10.5 upper then buying a commercial version of DD's MK18.... unless you plan on putting on an adjustable gas system. The ejection ports are huge and not to mil-spec.

3 years ago I would have chosen a MK18, but knowing what I know now I'm glad I waited and now have a 11.5" BCM KMR (govt. Profile barrel). I don't utilize or need a full blown 1913 rails and now use URX3.1 and the KMR for my rifles.

Length: how important is that to you? I went with the 11.5" from all the recommendations of others and so far it's been a joy to shoot, I believe it provides (40% longer dwell time IIRC).

Suppressor: I own a 762-rc and have the 5.56-rc in pending status right now. Surefire's are generally louder, and more expensive.... But the mounts are amazing/ less poi of any suppressor I've shot, and less blowback.

My 11.5" KMR has been great out off the box.... But I'll probably still add an adjustable gas system (like the govnah) but wanted to wait until I could shoot the 5.56rc with it to see if it was necessary.

[markm]

Watch out for those overgassed DD Mk18 "civilian" versions. Pappabear just a Mk18, and the AAC mini 4 works cool on it... and keeps the nose from being too heavy. You'd think it'd be loud, but the reduced baffle stack on the mini actually makes the port snap milder. We shot it with no ears and it was doable.

[Koshinn]

Yeah the mini 4, being less effective due to less volume and fewer baffles, redirects less gas back into the system thus less noise out of the port. End result being that it'll be as quiet or quieter than a larger silencer on a semi auto outdoors.

Steyr, go with a Noveske mk18, they're perfect with a h3 and springco blue!

[MistWolf]

Let's get to what I feel is the heart of the matter-

I like the Colt 6933 for what it is, a super light SBR without a ton of crap on it. I also worry the lightweight barrel may not be the best barrel for regular suppressor use

There is nothing wrong with getting another upper, or even a complete rifle simply because you want to, but reality is, while the lighter barrel will wear faster from heat than a heavier barrel, the 6933 will serve you well until the barrel is shot out

[steyrman13]

If you like the ris ii rail and look and like the 11.5, BCM sells that configuration with bfh as well.