DD Mark 18 Blowback Issues

[kmc0929]

DD Mark 18 W/AAC-M42000

I used an ACOG so unfortunately my face typically has to be right up against the charging handle. The Gas Blowback is just too much, after 5 consecutive rounds I have yet to find anyone who can push through it.

I have added a Gemtech SBC; PRI Gas Buster, and the H2 buffer.

My last shot will be a heavier H3 buffer... Any other suggestions?

[tylerw02]

Have you considered an adjustable gas block?


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[bighawk]

The DD MK18 barrels are very generously gassed.

My DD MK18 wears the AAC 556SD full time and Has a Micro MOA Govnah gas block designed specifically for the DD MK18 barrel.

I run it with an H2 and a blue springco with the gas port set to .052 and functions 100% with the can. Gas to the face is minimal and very tolerable

[Slippers]

It doesn't help that you're running a m42k either. That's a gassy can. Definitely try the H3 and consider an adjustable gas block.

Obviously this doesn't help you right now, but DD can custom build an upper with a crane spec port if you ask.

[Hero]

Have you considered an adjustable gas block?


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Best decision I made.

[markm]

The DD MK18 barrels are very generously gassed.

Yeah. I'd guess that port is .080 or greater. Which is already WAY TOO MUCH gas for a non suppressed weapon. An insertable port or adjustable block is mandatory here.

[bighawk]

Best decision I made.



Without a doubt.. Mine appears to bleed off a fair amount of excess gas at the port so its pretty mild to the face.

[bighawk]

Yeah. I'd guess that port is .080 or greater. Which is already WAY TOO MUCH gas for a non suppressed weapon. An insertable port or adjustable block is mandatory here.

I recall reading they are .081/.082 which seems crazy

When its time to replace it I will get a barrel with the proper gas port size.

[nate89]

For those who have tried both, is an adjustable gas block or insert a better option? I assume the adjustable gas block has the advantage of turning down the gas with the can on to the point where it would not work reliably with it off, and being able to turn it back up when the can is off. I like the simplicity of the insert, and would be more reliable in theory. I suppose the best option is getting a barrel that is gassed correctly..

[jackblack73]

Have you tried the silcone caulk on the charging handle trick?

[Jwknutson17]

I had a .082 and .084 Mk18 factory barrels. The only way to mitigate that huge port is an adj gas block, or buy another barrel. Band aid fixes with buffers and springs on that port with a can, don't do much. Been there, done that.

[Iraqgunz]

One thing that will help a little with eye relief is to get a KRAM from Macedon Defense. Or Google it as they are sold at Primary Arms and Weapon Outfitters.


DD Mark 18 W/AAC-M42000

I used an ACOG so unfortunately my face typically has to be right up against the charging handle. The Gas Blowback is just too much, after 5 consecutive rounds I have yet to find anyone who can push through it.

I have added a Gemtech SBC; PRI Gas Buster, and the H2 buffer.

My last shot will be a heavier H3 buffer... Any other suggestions?

[Iraqgunz]

Rumor has it, the newer production DD stuff is going to have a smaller port. I would contact them and ask about a swap out. Short of that, I would consider an adjustable block or contact Clint at Black River Tactical about an insertable gas port.

[JulyAZ]

Rumor has it, the newer production DD stuff is going to have a smaller port. I would contact them and ask about a swap out. Short of that, I would consider an adjustable block or contact Clint at Black River Tactical about an insertable gas port.

Do you know what size is to be expected?

[Iraqgunz]

Nothing solid, but much smaller than previous.


Do you know what size is to be expected?

[Clint]

Try contacting DD.

We've had a few reports of them replacing customer barrels that were "not cycling properly due to being overgassed when suppressed" with new mill spec .071" port barrels.

That's worth a shot and will help with the suppressor, but won't be small enough for dedicated suppressed.

If not, give us a shout here or at info@BRT and we'll take care of you.

[jpmuscle]

Rumor has it, the newer production DD stuff is going to have a smaller port. I would contact them and ask about a swap out. Short of that, I would consider an adjustable block or contact Clint at Black River Tactical about an insertable gas port.
Data point. My brother ordered a new DD mk18 upper from brownells a few weeks back. Best I could approximate the port is .073

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[vicious_cb]

Always try the cheapest solution first. AR gas vent, $38.
45765

[JoshNC]

It doesn't help that you're running a m42k either. That's a gassy can. Definitely try the H3 and consider an adjustable gas block.

Obviously this doesn't help you right now, but DD can custom build an upper with a crane spec port if you ask.

This. You could consider a BRT gasport. And as Slippers can attest, the Gemtech suppressed bolt carrier is awesome with a can. Definitely worth the cost.

[JulyAZ]

Nothing solid, but much smaller than previous.

I've confirmed with DD, the new GP size is .072. Where the previous size was .081.

[scooter22]

I had a .082 and .084 Mk18 factory barrels. The only way to mitigate that huge port is an adj gas block, or buy another barrel. Band aid fixes with buffers and springs on that port with a can, don't do much. Been there, done that.

This.


Try contacting DD.

We've had a few reports of them replacing customer barrels that were "not cycling properly due to being overgassed when suppressed" with new mill spec .071" port barrels.

That's worth a shot and will help with the suppressor, but won't be small enough for dedicated suppressed.

If not, give us a shout here or at info@BRT and we'll take care of you.

You have 3 options as far as real solutions:

1) BRT GP insert/GB. I got one for my BCM 11.5", and it's great.

2) Get a 16" carbine barrel and have it cut-down/threaded(/GP opened up, if you're not going to run dedicated suppressed).

3) Adjustable GB. Not a bad solution, but the worst out of the three IMO.

[Glass04]

I've confirmed with DD, the new GP size is .072. Where the previous size was .081.

I'm in the same boat with my DD MK18 and just got a response from customer services saying that they are processing my RMA. I'll create a summary post once the situation is resolved via customer service. Worth a shot to see if I can get my upper rebarreled with the proper port sizing.

[JulyAZ]

I'm in the same boat with my DD MK18 and just got a response from customer services saying that they are processing my RMA. I'll create a summary post once the situation is resolved via customer service. Worth a shot to see if I can get my upper rebarreled with the proper port sizing.

Here's what happened with my RMA.
https://www.m4carbine.net/showthread.php?t=197866

[Serious Account]

I've confirmed with DD, the new GP size is .072. Where the previous size was .081.

Hmm.. Isn't that a bit small? Why not .076 or .078?

[nate89]

Here's what happened with my RMA.
https://www.m4carbine.net/showthread.php?t=197866
Quite the example of customer service. Good on DD, makes me confident with the v7 I just ordered, should be here on Wednesday.

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[tom12.7]

Hmm.. Isn't that a bit small? Why not .076 or .078?

Not really, this porting is more in tune with 5.56 ammunition users with silencer options using an H2ish buffer. This leaves options that allow function more with the variables that they could be presented with. Many possible issues could be remedied with simple buffer swaps then what could be had with a larger base port.

[mdoan300]

Daniel Defense customer service was above and beyond my expectations.

[scooter22]

Hmm.. Isn't that a bit small? Why not .076 or .078?

No. FWIW, Crane spec is 0.070 for 5.56


Official Kremlin Transmission

[Serious Account]

I see... But would .072 be enough to run underpowered ammo or in adverse conditions? My understanding is that buffer replacement can only do so much

[scooter22]

I see... But would .072 be enough to run underpowered ammo or in adverse conditions? It could be enough. My understanding is that buffer replacement can only do so much Correct. Start with a proper GP diameter.

There are many variables to consider when discussing ammo and adverse conditions. It's not simply A+B=C. It really depends on your rifle.

[Serious Account]

Thanks! BTW.. What do u guys think of this statement from BCM regarding SBR and reliability? They feel that 11.5 inch SBR is more optimized than 10 inch. Sorry for going off topic a bit (there are already many threads on SBR that I don't want to create another one just for this question).


Q: Why BCM chose the 11.5" SBR over the 10.5"

I get this question a lot. It is a good one. When we spec our program we can build anything we would like, so we sat down and looked at the pros and cons.

First Statement: I know a good 10.5" SBR can run very well. I personally own a semi MK18 type and it runs great. No problems.

A: Dwell time.
Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).

The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.

Last Statement: For those folks who have a 10.5" that works very well, I would reply; me too. (see first statement)

If I had to "go to war" with a AR15 Carbine, I would grab the BCM 11.5".

[Clint]

Thanks! BTW.. What do u guys think of this statement from BCM regarding SBR and reliability? They feel that 11.5 inch SBR is more optimized than 10 inch. Sorry for going off topic a bit (there are already many threads on SBR that I don't want to create another one just for this question).

Yes, the 11.5" and 12.5" carbines have a better blend of operating parameters than the 10.5".

This should translate into a wider range of function.

[Iraqgunz]

I have seen numerous examples of 10.3"/10.5" that don't always run (either overgassed or undergassed). 11.5" seem to be much more forgiving whether it be gassing or ammunition.


Thanks! BTW.. What do u guys think of this statement from BCM regarding SBR and reliability? They feel that 11.5 inch SBR is more optimized than 10 inch. Sorry for going off topic a bit (there are already many threads on SBR that I don't want to create another one just for this question).