10.3" pistol/SBR build questions

[black22rifle]

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?

[OrignalRECIPE73]

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.

[black22rifle]

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?

[OrignalRECIPE73]

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.

Edited

[JG007]

Doesn't every thread talk about the DD being over gassed?



*why waste time and money on the pistol? sbr it asap , just the pistol parts, Sig brace and tube, pretty much cover your stamp

[black22rifle]

Yes many people say the DD 10.3 is overgassed that's why I'm adding the syrac. The plan is to keep it a pistol until I get the stamp.

[sidewaysil80]

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.

Here is the actual power point that goes over the MK18.
http://www.dtic.mil/ndia/2003smallarms/john.ppt

Just out of curiosity, any particular reason you are going with the DD barrel and adj. gas block as opposed to something with a smaller gas port?

[black22rifle]

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.

[OrignalRECIPE73]

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.

Apologies black22rifle, Didn't know the port size was 16 thou bigger. Learn somethin new every day haha.

[lawman1380]

I run a 10.5" DD...and I have ran Sprinco red and blue springs with a Spikes H2 buffer no problem suppressed or unsuppressed