Need some advice from those who have more experience. I've got a Colt SOCOM lower with the M4A1 roll mark, and I was lucky to get a Gen 1 LMT SOCOM (black) from a good buddy in the clone game. Right now it's rocking a pin/weld Block II M4A1 upper and I've sent in my form 1 and got it engraved.

Help me decide between a Block I and II. Am I correct in that the M4A1 Colt lower is even appropriate for the Block I? What are you all doing for barrels, Colt M4 FSB cut down by Adco? Block II parts seem hard to impossible to locate. I missed out on the Bronwells stripped block II uppers, not sure if that's gonna happen any time soon.

So what say you guys?

Accidental page ownage: just imagine the upper shrinking in a few months lol

I went with a complete Colt M4A1/6920SOCOM for my Block II, just got an M4/6920 OEM1 for a block I/MK18 mod 0 clone. From what I've read on here, it doesn't really matter because the real deal is either an M16 lower for the block I and an M4A1 lower for newer block IIs. I'd defer to the more experienced cloners out there, but if you want to save cash just build a block I upper and swap them out on that lower you picked up. As far as barrels, I think I've read that cut down govt profile/M4 barrels were used in the block I's, correct me if I'm wrong.

There have been plenty of Mk 18s built with M4A1 lowers and Block I CQBRs on M4 lowers. Since all of our lowers aren't even 100% correct, it doesn't matter all that much anyway. But, your lower is appropriate for either build.


If you're building a Block I:

• Find a 16" gov profile barrel (Colt, DD, LMT, etc…) and have ADCO or a similar shop chop it down.
• You can buy a factory Colt barrel from SAW that's been modified with "reliability improvements" for an outrageous price.
• There is also another vendor (that shall not be named) that sometimes carries factory Colt 10.3" but they're currently out of stock with no ETA for restock.
• You can find places that sell factory DD 10.3" barrels with an FSB but some people don't like them due to their generous gassing.

Of the 4 options listed, the first is probably your best bet right now. 16" gov profile barrels with factory FSB usually go for pretty cheap on the EE because most people don't want them. They will take them off their new factory ARs and sell them for cheap. You can grab a barrel in the $150-200 range and have ADCO chop it for $65+shipping. You'll end up well below $300 for a barrel that's as clone-as-you-get.

If you're building a Block II, your options open up quite a bit since it's not as important to find something with a factory FSB. Ballistic Advantage sells a affordable hanson 10.3" barrel. You could also get any carbine-gas barrel for cheap off the EE (BCM, Bushmaster, etc…) and have it chopped by ADCO.


I have not seen that to be the case. FDE Mk 18 rails aren't sold individually by DD any longer, but they seem to come up on the EE fairly often and the prices are still reasonable ($375-425). There are also complete uppers w/ BCG that pop up, often for $1k or less.


It's really personal preference. They're equally capable builds. The Block II is a little bit heavier and "feels" bigger/heavier in the hands, but you get the stiffer FF rail with more rail/hand space to make up for it. The Block I feels really good in hand, very well balanced, but can feel cramped if you throw light, laser, etc… on there. In typical ARFCOM fashion, the true answer is to do both. You can just share the lower between the two uppers and enjoy each one.

Just for clarification, aren't they typically BOTH govt' profile under the handguard?  I thought CD said they don't typically use SOCOM barrels for MK18's.  Not that it would matter since you can't see, well on a block 1 you can't.

No they've never used SOCOM barrels on CQBRs.

Govt and SOCOM on 14.5. Not the 10.3"

I hope that doesn't pee on NenoRevada's parade.  

Man both the Block I and Block II must be light as a feather with just irons and no other stuff on it.

Ha, no I stuck with the SOCOM profile on my CQBR build mainly because it was already there and I set it up for suppressor use anyways. Hope the real purists arent offended! I barely got my form 1 for the Block I off today, can't wait to cut the govt profile down it feels lighter than the CQBR already.

Correct.


CD

 
So, for a Block II - anyone know the Hansen 10.3" gas port size?  Or if picking up a Colt 6920 16" M4 barrel or similar (my original thought since finding a 10.3 seems impossible, at least lately) does the gas port need to be changed when adco cuts it down to 10.3??  I keep reading about guys running .4x ,.6x. .7x ports, etc - so confusing.  Would run a Socom-RC on it mostly, and only shoot XM193, 855, or Black Hills or comparable handloads...worst case would be Wolf Gold, which is XM193 spec essentially.  But no steel case wolf/tulla anything like that.   Since I have the Block I, been thinking about putting together a Block II upper to go with it.


 

I don't think BA has published their port size but I'm sure you could call them and ask them. They're a great company.

For port size, yes, a 16" Colt barrel will need to be opened up. The 16" factory barrel has a port size of something like .063 or .064. ADCO will typically take care of that automatically and open it up to their own specs. If you want the Crane-spec port size, it's .070. .070 will cause you to short-stroke (with an H2) with some ammo, so a lot of guys will have it opened up to around .074.

With .074 you'll be able to run typically weak ammo (Like PMC .223) with the standard carbine spring and H2 buffer.

 
Interesting, thanks - not sure why guys were wanting uber small ports them, maybe I misunderstood the post.  Since I pretty much baseline every build with a Blue Springco and H2, I'll definitely lean towards .70 or a little north of there.

Good to see we're still discussing gas port sizes, even though i haven't been here for a while lol BTW, I run a .043 on mine suppressed and it purrs like a kitty, super smooth.

Not to nitpick, but for clarity's sake, I thought I'd post this here. It was part of a conversation between Caroline Britton (Daniel Defense) and me in July 2015:

No worries!

The barrel you have now is the commercial barrel used so that a wider range of ammo can be used by the end user.  It has a gas port diameter of .081.  The mil-spec barrel I plan to use for the replacement for you has a .072 gas port diameter and works great suppressed or unsuppressed.

After extensive testing, we found that .081 commercial was the ideal diameter to run reliably with the widest range of ammo possible.  Some believe this to be over-gassed and sometimes it will cause malfunctions if used in conjunction with a suppressor, however, it is ideal for the masses.

The barrel you are getting will run perfectly fine suppressed and unsuppressed in conjunction with the mk12 gas block we will get on there as well. J

Best Regards,
Caroline Britton
Warranty Administrator, Sales/Quality

For reference, I run a Colt H2 buffer, Colt carbine spring, shoot unsuppressed, and my gun runs flawless and ejects the brass consistently between 3 and 4 o'clock.

.07 is middle ground between best spec for suppressed and unsuppressed with mil ammo.

People wanting smaller are trying to optimize suppressed shooting, mostly through adjustable gas blocks.

How do those buffers run on top of each other. You've got to be short stroking.

I figure you mean the spring.

I am pretty sure i have a .081 gas port as my build is a HCS upper, but Kevin sent me a link to the barrel from DSG arms, so I'm going to say it came from there and was the commercial port.

However, I run an H2, regular carbine spring, shoot unsupressed as well, and I have the same pattern.... I cannot say it runs flawlessly suppressed though. It had some issues, but shooting at night, it was difficult to determine what was happening....

When it comes to buffers, two is one, and one is none. That's how Tier 1 operators roll.

Finshed up the paint, got some outside pics finally.  While I didn't forget to flip the safety/selector lever, I did forget about the TD grip lever and the tape switch lol.  I'll hit those and should be good to go. KAC Vert grip is painted as well, but the TD works so much better with the tape switch.  Overall I'm pleased, just wanted something not strait up tan, but not overly involved, either.  This is just Aervoe Sand and Earth Brown.





 
 

I would not recommend using a blue spring with that setup. The blue spring is optimizing to provide more pressure to counteract an over-gassed system. If you have .070-.074 your rifle will not be overgassed, it will be just right. An H2 and standard carbine spring (Springco white) is what that gas port size was designed around (same that's used on mil M4s).

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Probably 99% of people that shoot DD factory barrels are doing it unsuppressed, so their decision to run a larger port makes sense from that perspective. I'm sure it's reduced the number of complaints and warranty problems that they see - especially given the amount of weak ammo available commercially.

The problem though, is these short barrels experience accelerated gas port erosion compared to their 14.5" or 16" brethren. So if you're already starting big, by the time you get thousands and thousands of rounds through it, it's opening it up even more.

I have seen DD barrels malfunction while shooting suppressed including one I used to own. My issue was that it was an FSB (Block I) build so I didn't have a reasonable way of taming it down. If you have a DD barrel on a Block II build, the solution is pretty easy - get a cheap, adjustable gas block and keep on shooting.

Buffer springs are also wear items that many people forget about and don't replace often enough. That can cause just as many function issues as an oversized gas port can. Remembering to replace your spring at regular intervals or getting a standard weight chrome silicon spring is definitely a piece to the puzzle of keeping a CQBR running good.

But no matter what, barrels are wear items. You'll eventually shoot them out. And for less than the cost of a case of ammo you can rebarrel it with ease in 30 minutes. DD barrels are just fine as long as you know what you're getting in to. But if you never plan to shoot weak ammo or you plan to shoot a good amount suppressed, I can't see the argument of going with a factory DD over getting a chop job from ADCO.

 
Makes sense, after re-reading a few posts I"m starting to understand the relationship better.  I've got a std spring I will switch over test it out - thanks :)

I agree with you. I think a baby govnah might be on the option table once I find an nt4, can afford it, or i decide to go rc and can afford that as well Lol

It was really tough to determine what the cause of the issues were that night. But im sure it was influenced by that larger gas port. I also need to look i to getting a higher grade h2 buffer I suppose. :/ if there's a difference in performance to them..

You're all mixed up.  Eothings on Block II, Big Aimpoints on the CQBR.   WITH a CCH.  

It's pretty sweet though.

Almost ready for the night shoot.

I took the TA01 off the FSB upper and put an old 552 on there, as requested from the higher ups.

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So cool... very well done

I'm contemplating transitioning a 10.5" FSB upper into a mk18 build and had a couple questions, I lurk here a good bit and know a lot you guys have a ton of knowledge on whats out there in the wild and which of those items are considered "clone appropriate"

In the original post of this thread it states the following in regards to rear BUIS and Pistol Grip spec:
M4A1 CQBR Block I: Rear BUIS: LMT Fixed, MATECH, & others | Pistol Grip: A2, ERGO & others
M4A1 CQBR Block II: Rear BUIS: MATECH, KAC 300m, & others | Pistol Grip: A2, ERGO & others      

My question is in regards to the "others" in these two categories. Where could one find a list of the "others"? or is that even a thing?
I mainly ask because i prefer the KAC 200-600 micro as oppose to the other listed BUIS, and I'm not a big fan of the A2 and ERGO pistol grips and was looking for acceptable alternatives.

Magpul mainly

Others because just about everything has been seen in the wild.

Shorties.

KAC 200-600 micro is fine.

 

Would you be offended if I played with myself while looking at this pic?

Getting closer, although I'm not sure how I feel about the black Surefire mini scout

It could be tan in a matter of minutes.....

Krylon will cure what ails you.

This guy knows.

I like where your head is at

Shake...rattle.... and WOAH!!

That's basically what happens...

Best solution.

It's what I did right after I got mine out of the package

 

Couple of spare slick Mk18-1 somewhere northern Iraq.  (spare guns, hence the carrying handles)




course they are small compared to some of the other ordanance.




CD

freaking awesome. nice to see your "handle's" rebreather in the middle.

Wow, thanks so much for sharing CD! Are the uppers marked in any uniformed fashion?

Awesome!

I think your magpul is on sideways.

But my eotechs in the road

Out of curiosity I am thinking about building a CQBR I upper what length rail would I need for the FSB.  Looking at Centurion Arms 7" C4 or 9" C4.  Yes I know its not the correct rail but it is what I want to go with.  I already have a CQBR II upper.

The block 1 uses the knight carbine length knights ris.

If you're wanting to build a block 2 CQBR, the rail you seek is the mk18 risii FSB which is a unicorn.... Or can be made if you know the right people and have the right parts.....

But since you are just looking for a FSB rail, the carbine length is what you seek...should be a 7" with cutout.

I spoke to a rep at centurion a couple of weeks ago, and they stated those were next to be run since brownells had purchased a bunch of them, but it would be several weeks until they were out.

I think the CQBR2 marked ones appear to be Cranes earlier attempt to mark them.  Majority that I see now start with 1000xxx on the 10.3" and 1400xxxx on 14.5" uppers and this is SOCOM wide.  This is done to put on the property books as those without the markings had a tendency to walk

14.5" with Surefire flash suppressors






CD