View Full Version : BCM/DD 14.5 Gas Port Sizing
There are already a lot of BCM vs. DD threads, but I would like to ask a more pointed question:
Can anybody compare the gas port sizes of the 14.5 middy BCM and 14.5 middy DD uppers? I hear constantly about how smooth the BCM shoots, but not much about the DD. I assume this is partially a function of BCM’s small gas port size; I would like to know how the DD compare. In theory, assuming they have the same size gas ports, they should both run equally smooth when setup with the same length gas systems, buffers, muzzle attachments, etc. Thanks for the help.
I am curious as well. I've been trying to make the very same decision. Any help would be appreciated.
Dirtyboy333
11-10-10, 18:40
Is there a trade off between "soft shooter" and reliability? The reason i ask is because i would think that if you had two of the exact same middies with 1 having a smaller port that even though it would be slightly softer shooting in an already soft 5.56 it would also be more prone to short stroking when its dirty or weak ammo etc... Again, this is a question not fact lol
I have also been wondering the same question as you and haven't had any luck...in the meantime it got me thinking of the question above...I would be glad to measure for you but i have a DD carbine barrel. Hopefully sum1 will have the specs...
There are already a lot of BCM vs. DD threads, but I would like to ask a more pointed question:
Can anybody compare the gas port sizes of the 14.5 middy BCM and 14.5 middy DD uppers? I hear constantly about how smooth the BCM shoots, but not much about the DD. I assume this is partially a function of BCM’s small gas port size; I would like to know how the DD compare. In theory, assuming they have the same size gas ports, they should both run equally smooth when setup with the same length gas systems, buffers, muzzle attachments, etc. Thanks for the help.
Your not going to get any info on this as very few people are going to have both barrels, and even fewer are going to have the ability to measure the GP's.
C4
I ran across something the other day but I cannot remember where... It said the DD gas ports are .075 inches. I can't cite the source so it may be incorrect.
D. Christopher
11-14-10, 21:18
CQC.45,
I've got a DD 14.5" Mid-length Lightweight and the gas port is .625" on that one. I've also got a ruined (bulged) BCM 14.5" Mid-length barrel hanging on the wall of a friend's gun room that I can measure, but it will be sometime later this month before I can get to it. I wrote down all the specs on that BCM barrel when I did the build but it's on a yellow legal pad somewhere. I need to find it and put all those specs in my database anyway so I'll see if I can find it tomorrow.
Robb Jensen
11-14-10, 21:19
CQC.45,
I've got a DD 14.5" Mid-length Lightweight and the gas port is .625" on that one. I've also got a ruined (bulged) BCM 14.5" Mid-length barrel hanging on the wall of a friend's gun room that I can measure, but it will be sometime later this month before I can get to it. I wrote down all the specs on that BCM barrel when I did the build but it's on a yellow legal pad somewhere. I need to find it and put all those specs in my database anyway so I'll see if I can find it tomorrow.
Your gas block seat might be .625" (aka 5/8"), there's no way in hell your gas port is 5/8".
D. Christopher
11-14-10, 21:28
Your gas block seat might be .625" (aka 5/8"), there's no way in hell your gas port is 5/8".
Sorry, I was going by the data on the DD site.
Robb Jensen
11-14-10, 21:30
Sorry, I was going by the data on the DD site.
DDs gas ports for CAR gas guns (14.5-16") is .0625"
D. Christopher
11-14-10, 21:35
DDs gas ports for CAR gas guns (14.5-16") is .0625"
You're right and they're wrong.
https://www.m4carbine.net/attachment.php?attachmentid=6561&stc=1&d=1289792024
justin_247
11-15-10, 04:20
You're right and they're wrong.
https://www.m4carbine.net/attachment.php?attachmentid=6561&stc=1&d=1289792024
Somebody definitely fat fingered this. It's .0625"... period.
gotm4 is 100% correct.
It wasn't fat fingering. That is bbl diameter/gas block diameter. That is for their light weight barrel. If you look at standard barrels it is larger. They don't have the spec sheet labeled clearly.
D. Christopher
11-15-10, 09:51
They have the spec sheet labeled clearly, but I didn't post the whole thing, only the Materials & Construction portion that shows the Gas Port Diameter. If you go to their site and look at it you'll see that I only posted the lower portion of the spec sheet for the 14.5 Mid-length Lightweight barrel.
They have the spec sheet labeled clearly, but I didn't post the whole thing, only the Materials & Construction portion that shows the Gas Port Diameter. If you go to their site and look at it you'll see that I only posted the lower portion of the spec sheet for the 14.5 Mid-length Lightweight barrel.
They are not clear in that the gas port diameter is NOT 0.625".
Look at the 14.5 Mid-length Government profile:
Materials & Construction
* Barrel Material: Chrome Moly Vanadium Steel
* Barrel Type: Cold Hammer Forged
* Barrel Caliber: 5.56 NATO
* Barrel Twist: 1:7
* Barrel Length: 14.5″
* Barrel Profile: Govt Profile
* Barrel Gas System: Mid-Length
* Inside Finish: Chrome Lined
* Outside Finish: Military Specification Heavy Phosphate Coated
* Muzzle Thread: 1⁄2×28 TPI (Threads Per Inch)
* Gas Port Diameter: .750″
* Barrel Extension: A4
* Made in the USA!
So if what you're saying is true, they are use a 3/4" gas port on government weight barrels? They mislabeled the spec.
eternal24k
11-15-10, 11:22
I spoke with DD last week regarding those numbers, they are the diameter for the gas block, period.
Regarding the 16" port I was told that if their
memory serves [them] correctly, the gas port diameter on a 16” Middy barrel is around .070”.
so I can't imagine that it would be smaller for a 14.5"
D. Christopher
11-15-10, 12:04
They are not clear in that the gas port diameter is NOT 0.625".
Clear and accurate are two different things. I said that they labeled their spec sheet clearly. They did. I posted that portion of their spec sheet to show gotm4 where I got my incorrect data.
Clear and accurate are two different things. I said that they labeled their spec sheet clearly. They did. I posted that portion of their spec sheet to show gotm4 where I got my incorrect data.
Are you really going to sit here and argue semantics? Their sheet is unclear that they say the gas port diameter is .625" when clearly they meant gas block diameter/barrel diameter.
Dirtyboy333
11-15-10, 22:39
it means barrel diameter at the gas port. its a little unclear
Any updates, I would still like to know :)
Dirtyboy333
10-02-11, 12:36
My DD 16" CAR is .062". Couldn't tell you what the 14.5" is. Although, i heard they're usually the same.
In the past I have done quite a few upper builds using the DD non-CHF 16" barrels. Very accurate barrels but I did notice quite a few with gas port sizing in the .058 range. Some needed to be opened up and I generally open them up to the .062 sizing. I am not sure on the newer barrels. Haven't used a DD barrel for a build in awhile.
Eurodriver
10-02-11, 13:50
In the past I have done quite a few upper builds using the DD non-CHF 16" barrels. Very accurate barrels but I did notice quite a few with gas port sizing in the .058 range. Some needed to be opened up and I generally open them up to the .062 sizing. I am not sure on the newer barrels. Haven't used a DD barrel for a build in awhile.
Aloha Surf,
When you say "in the past", what do you mean? Past 2 years? 5 years?
I just built a dedicated suppressed upper with a DD 16" non CHF barrel. I did not measure the gas port, but I did not open it after I cut it down to 10.3". I am thinking if it is .058 it may be a bit too small.
I heard some full auto at Kokohead a while back. Was that you guys? :)
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