MK18 MOD1 Technical Thread

[kwilkin]

Just to add more confirmation to the over-sized gas port issue, here is a video from 2014 where a DD rep states that the gas port is "optimized...to function reliably with a wide variety of ammunition" (at about 1:07): https://www.youtube.com/watch?v=s3toPQwWw0s. I take this to read "oversized" for crap ammo.

Of course, I guess one has to rely on their legendary customer service to get your bolt and/or other parts replaced a head of schedule due to the rough operation of the system.

[bmg]

I also use the Syrac gas block to fix the oversized DD gas port issue.

[Sparky5019]

Tag; building MK18.

[Eurodriver]

I bought a 16" DD barrel and cut it to 10.3" without adjusting the gas port. Pinned the gas block and it runs like butter suppressed.

Even suppressing a "good" SBR with a "correct" gas port is going to over gas the weapon.

[Dirtyboy333]

That sounds nice! I'm thinking of cutting my 16 inch back to 14.5 and pinning the brake. Did you notice any ill effects in accuracy after cutting your barrel? Since it's chrome lined?

[Quiet-Matt]

I own a DD MK18 and run a H2 with an "enhanced" Blue spring from Sprinco. The increased spring tension and buffer weight can remedy this felt recoil when using higher pressure loads, as well as reduce wear. I know some here have adverse opinions of the "colored" springs. It would be nice if you could choose whether or not you want the over gassed versions when ordering from DD. Anyone else running non-mil spec springs with these?

I've had the same setup in my DD 10.3" for a while now. Seems to do well.

[thecolter]

That's what I did on a suppressed SBR too. That Syrac really works well. I don't know what I'd have done with that barrel otherwise.

Suppressed use what my original intent for going with the Syrac to allow my to tune the system down once my can gets out of ATF jail without having to cut the rail to run a switchblock. Now, I don't mind the over-gassed DD barrel paired with an adjustable gas block. I see it as beneficial. The way I now look at is that I have the flexibility to run less than ideal pressure ammo (Wolf/Tula, PMC Bronze, etc) if the need arises by simply adjusting the gas block. This will yield a wider range of ammo that will still function reliably and being 'properly' gassed, given minimal and fast 'tweaking'.

I shot a 'Carbine match' over the weekend where a member of our group had issues with his complete factory LMT 10.5". He was running reloads (55gr Hornady over 24.5gr of TAC, .223 pressures) and had multiple misfeeds due to the rifle short-stroking. He ended up having to run a different rifle as the SBR would not fire the ammo without jamming. Now, I was running a similar load, but my DD barreled SBR ran 100%, because I was able to 'open up the gas' to compensate for the lower-powered ammo. I really see it as a benefit when paired with a quality adjustable gas block.

[markm]

I shot a 'Carbine match' over the weekend where a member of our group had issues with his complete factory LMT 10.5". He was running reloads (55gr Hornady over 24.5gr of TAC, .223 pressures) and had multiple misfeeds due to the rifle short-stroking. He ended up having to run a different rifle as the SBR would not fire the ammo without jamming. Now, I was running a similar load, but my DD barreled SBR ran 100%, because I was able to 'open up the gas' to compensate for the lower-powered ammo. I really see it as a benefit when paired with a quality adjustable gas block.

That load is very mild... even by .223 pressure standards. I used to run that load too.

[Iraqgunz]

And this is why people can't have good things. The MK18 and variants thereof were not designed to shoot low pressure ammo. Now we know why some companies opt to open up their ports.

Suppressed use what my original intent for going with the Syrac to allow my to tune the system down once my can gets out of ATF jail without having to cut the rail to run a switchblock. Now, I don't mind the over-gassed DD barrel paired with an adjustable gas block. I see it as beneficial. The way I now look at is that I have the flexibility to run less than ideal pressure ammo (Wolf/Tula, PMC Bronze, etc) if the need arises by simply adjusting the gas block. This will yield a wider range of ammo that will still function reliably and being 'properly' gassed, given minimal and fast 'tweaking'.

I shot a 'Carbine match' over the weekend where a member of our group had issues with his complete factory LMT 10.5". He was running reloads (55gr Hornady over 24.5gr of TAC, .223 pressures) and had multiple misfeeds due to the rifle short-stroking. He ended up having to run a different rifle as the SBR would not fire the ammo without jamming. Now, I was running a similar load, but my DD barreled SBR ran 100%, because I was able to 'open up the gas' to compensate for the lower-powered ammo. I really see it as a benefit when paired with a quality adjustable gas block.

[NongShim]

While everyone speaks about the DD-railed Mark 18 CQB uppers, why isn't any mention made of the Larue-railed uppers?

We had a number in Baghdad from 2007-08 (including my Command Sergeant Major's) built on M16A1 lowers with SOPMOD stock. I don't recall the (stainless) barrel maker.

Random photo:

My terminology isn't very good. My reference to DD RIS2 uppers is only to the current incarnation or standardization. Still see some of the CQBR uppers with normal FSB and KAC RIS floating around. I never even think about those LaRue ones when this topic comes up because people usually wonder about "standardized" configurations.