6x6.8 spc build help

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DeereGreen

Member
I’m having cycling issues with my new build. Here are the details.
22” X Caliber barrel , r+2 gas with syrac II adjustable gas block.
Starline brass , cci 450, 58 gr vmax , 31 gr IMR 8208 xbr @ 2.250”

The lower I plan to use has a magpul MOE rifle stock with rifle buffer and spring. With the gas block fully open it will not lock open on an empty mag.

I put it on another lower with a carbine length tube with a h2 buffer and it runs good with the gas block half open.

So what do I do to get it to run on the rifle stock ? I’d already considered getting one of the silent capture buffer assemblies. I think they will work in the rifle tube with a spacer. I just don’t know which weight ?
Will a h2 silent capture system with a spacer in a rifle tube behave the same way as the same h2 silent capture system in a carbine tube ?
Also plan to run a can if it ever makes bail. How much less gas will that require (Dead Air nomad 30) ?
 
I haven't messed with the silent captures but I'd try a lighter weight buffer and spring knowing it runs with a carbine system. I run all carbine stocks on my stuff because I could be in a Tshirt or a heavy parka throughout the season and it allows LOP to be adjusted on the fly as well as different framed shooters that may be using it.

I also use AGB and when tuning I screw them all the way in (closed) and back it off 8 clicks and start there, it's pretty close usually. The can will DEFINITELY add back pressure but I do hunt sometimes in Illinois so I have to tune without the can. Honestly it's only a few clicks difference anyway so no biggie being a little overgassed
 
Kino M said:
I haven't messed with the silent captures but I'd try a lighter weight buffer and spring knowing it runs with a carbine system. I run all carbine stocks on my stuff because I could be in a Tshirt or a heavy parka throughout the season and it allows LOP to be adjusted on the fly as well as different framed shooters that may be using it.

I also use AGB and when tuning I screw them all the way in (closed) and back it off 8 clicks and start there, it's pretty close usually. The can will DEFINITELY add back pressure but I do hunt sometimes in Illinois so I have to tune without the can. Honestly it's only a few clicks difference anyway so no biggie being a little overgassed
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That’s the problem . A rifle buffer is a rifle buffer there aren’t different weights like there are with carbine buffers.
The silent capture buffers are carbine length and come in different weights and will work in the rifle length tube with a spacer.
 
What upper? I've had problems with a couple bca gen2 sidechargers cycling or even ejecting due to not capturing enough gas. Move the same barrel and gas system over to a bca rear charging and 3 to 4 o'clock ejection and locks back on an open mag. I think most mass produced barrels have gas ports that are a bit oversized to ensure cycling and fewer complaints. When you get into custom rifle plus 2 gas lengths with conservative gas port sizes things can get finicky. My custom 24" rifle plus 2 gas 6 Hagar on a side charger is acting just like yours so I just put a quality carbine stock set up on it and called it good. Like Kino says it gains adjustability for different scenarios.
 
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popper43 said:
rifle plus 2 gas - have no idea what that is but either change to carbine stuff or increase port diameter.
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Rifle +2 means it's 2" longer than the traditional rifle length gas tube. It's very beneficial on calibers bigger than the standard 556, especially on AR10 applications of any caliber.
 
A lighter carrier would have a similar effect to a lighter buffer, ie if you're using an m16 style, try an ar15 style. You can also take apart the rifle buffer and swap a weight or two for a lighter spacer.
 
Imo this recent AR craze led to a lot of mass produced parts. The inside dimensions of the carrier has to jive with outside dimension of the bolt to capture gas. The gas rings only seal the front. Not to mention the gas vents drilled in the carrier. Most of my issues have been with side chargers from bca but I've been round and round with some of them. I would swap just the carrier and eliminate that. Then swap in another bolt if you have one. At least it runs. Some of mine wouldn't even extract. Could be the gas port just needs to be .002 or .004 bigger.
 
Only thing new on this build is the barrel and gas tube.
Carrier and arp super bolt been running in a 6.8 spc for years.
did run it on the lower with the carbine stock.
 
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