I am in the process of building a 10.3" pistol that I plan on turning into an SBR and eventually adding a silencer, but I have a few questions in regards to the buffer spring, buffer, and extractor.
The upper parts are:
BCM4 upper
DD 10.3" barrel
Syrac gen 2 adjustable pinned gas block
KMR 9
BCM comp
Since I will be going with an adjustable gas block will that eliminate the need for the extractor o ring and a heavy buffer and spring combo? I have spare H2 and H3 buffers that I can play with, but I dont know which buffer spring to go with. When I add a silencer will I have to change the buffer/spring combo?
I run a spikes standard carbine spring in mine with an H2. I’m an 11.5 but my friend runs a factory LMT 10.5 with an H buffer and the same spring. Both of our uppers have the 51tooth aac mount and shoot the m4-2000 reliably suppressed.
Buffer/spring and extraction problems are usually caused by the gas system aren’t they? So theoretically I shouldn’t need the o ring in my extractor with the 10.3 because of the adjustable gas block?
That depends on the setup that you run, I’ve heard mixed views about 10.5 being under gassed, but from my experience and after talking to the tech at Daniel they run theirs a tad on the lean side anyways due to the shorter barrel (on the 10.3 mk18) and the fact that it’s a popular setup to suppress so that’s the reason for them producing them a taste on the lean side. That’s what I was told like I said from the tech at DD, however come to find out that’s actually not the case. After doing a little reading you may need the extractor mod, as well as the block to tune your gas pressure.
The DD 10.5" barrel gas port is a whopping .086" and is certainly over gassed. This is to facilitate the function of the lower cost, underpowered “cheap stuff” ammo. The NSWC Crane spec for the mk18 10.3 is .070", that will function reliably both suppressed and unsuppressed and does not require an adjustable gas block.
Since you are adding an adjustable gas block you can tune it and essentially “decrease” the port size of your DD barrel. With that being said, I would think you still require the extractor upgrade. The actual MK18’s called for this modification and they had the proper gas port size. I think even if running the optimal amount of gas, it still alters the characteristics of the bolt function.
I wanted the shortest barrel regardless of the benefits an 11.5 has and the gas block was to fine tune it. In addition, my two other rifles have a bcm and fn barrel so I wanted to go with something else.
If I were building a 10.3 w/ adj gblock, I’d tune the gas to run on an h2 sprinco blue or a5h2 sprinco green.
I would also suggest extractor insert with either sprinco 5 coil, bcm enhanced, or colt gold springs. The bcm or sprinco 100% do not need an o ring, never had a colt, so I can’t say.
If you get the gas down extractor tension isn’t as big of a deal.
Have you checked a barrel and saw that it was .086? All the reports I have read online have said it is at .082. I have decided to drop the syrac and go with the govnah instead. I’m going to get a dual custom port with .070 and .082(factory) ports. Then when I get the silencer I will just get a new plate.
I’m running a DD 10.3" with H Buffer, whatever spring weight comes with a Colt 6920, ARMS #41-BL FSB, and stock Fail Zero BCG.
Has run fine with a hodge podge of loose ammo around the house. Everything from wolf to PMC to M193 and M855. Never a hiccup in a few hundred rounds since finishing the build a couple of months back.
I honestly have no idea what the gas port size is, but DD lists it as .750″.
I think DD is referring to the diameter of the barrel at the port with that figure, not the actual port diameter.
I’m glad to hear that your rifle runs just fine with an H buffer and a milspec spring though. I’m planning on getting a 5.56 SocomRC 2 when they come out this year and wasn’t sure if I would need to make any changes to my rifle. It’s a factory DD MK18. I’ve already bought an H2 just to see. I can’t stop buying stuff!!