Adjustable Gas Block on SFAR?

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hittman

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Using the Search feature on the upper right of this page …. You'll find lots of info in several posts on this subject,




 

KneverKnew

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Thanks.

Does the SFAR 20" take a standard rifle length gas tube, if I decide to install an adjustable gas block?

I hope to try an H3 buffer today. The H2 still had heavy overgassing signs, bad double ejector swipes on case heads. Generally happens with CAVIM 7.62 which seems a bit hotter than other standard milspec "nato" ammo.
 

Courageous Lion

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Has anyone fixed any function issues with their SFAR by simply swapping the Ruger 3 position GB for a different adjustable GB?
Try replacing the 3 oz ar 15 buffer with a 5.5 H3 AR 15 buffer. A standard AR 10 buffer is 3.8-4 oz. I have no idea why Ruger would use a 3 oz 5.56 buffer. And the bolt carrier is a lot lighter than a standard AR 10 BCG! And as for the GB? I took mine off and put a fixed one because for me? I'm never going to use a suppressor on mine. Mine was having bs issues about 150 rounds in. And it wasn't consistent. When I found a 3 ounce buffer in a .308 I thought WTF?? I think once the spring starts to set that they are using the trouble begins. System is moving too fast.
 
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KneverKnew

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I have an H3 buffer I'm pulling from another weapon. I feel like the spring is too long. Is a standard carbine spring good enough? Or shouldn't keep the longer SFAR spring until I can order a vltor kit?
 

KneverKnew

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FYI, I just spoke with Brian at Vltor about the SFAR. He said they actually tested their A5 system with the SFAR 308 in house and he says they determined the A5 was not compatible with the 308. Hmmm? 🤔

I sure would like to know what A5 components others are using that helped.
 

KneverKnew

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Try replacing the 3 oz ar 15 buffer with a 5.5 H3 AR 15 buffer. A standard AR 10 buffer is 3.8-4 oz. I have no idea why Ruger would use a 3 oz 5.56 buffer. And the bolt carrier is a lot lighter than a standard AR 10 BCG! And as for the GB? I took mine off and put a fixed one because for me? I'm never going to use a suppressor on mine.
I do have a suppressor to use so adjustable gas block is needed. If the H3 buffer, or possibly a stronger flat or braided spring doesn't help the over gassing issue with ruger's gas block I will try one of my Odin Works adjustables. I think that will do the trick. But I'd like to try and leave original if possible.
 

Courageous Lion

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I do have a suppressor to use so adjustable gas block is needed. If the H3 buffer, or possibly a stronger flat or braided spring doesn't help the over gassing issue with ruger's gas block I will try one of my Odin Works adjustables. I think that will do the trick. But I'd like to try and leave original if possible.
I am convinced the lighter bolt and the light 3 oz AR 15 buffer is the main issue. The gas PRESSURE on a .308 has to be higher than what it would be on a 5.56. What I see happening is a timing issue caused by the bolt travelling so fast that the rounds don't have enough time to come up in front of the bolt. And it starts happening after the spring that is supplied starts to set a bit. I think the H3 buffer will solve the issue for you. And if you run a suppressor, don't you cut off the gas? Or do you use #1 position? I'm ignorant on the suppressor question. And why would you want to use one on a .308 in the first place? Just curious...
 

Courageous Lion

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It "may" be the same. I have no way to measure them. If everything in the assembly, the BCG and the spring and the buffer were equal to a 5.56 I don't think I'd see the obvious tell tale signs on the brass of the system slamming into the brass so hard that it is actually slightly deforming it and it appears that the system is travelling too fast thus the issues folks are having. I slowed it down with the H3 buffer and it is working fine. Most of the extracted brass is landing 3-4 o'clock some slightly above the 3 o'clock mark. I see LESS of the telltale sign of the system going fast on the brass but there is still some there. It isn't deforming at all from what I can tell. It slides into the shell holder easily where before it wasn't. Something is not quite right in either the pressure or volume. I did put on a fixed gas block and measured the hole which is slightly larger than the #2 position but smaller than the #3 position.
 

KneverKnew

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I am convinced the lighter bolt and the light 3 oz AR 15 buffer is the main issue. The gas PRESSURE on a .308 has to be higher than what it would be on a 5.56. What I see happening is a timing issue caused by the bolt travelling so fast that the rounds don't have enough time to come up in front of the bolt. And it starts happening after the spring that is supplied starts to set a bit. I think the H3 buffer will solve the issue for you. And if you run a suppressor, don't you cut off the gas? Or do you use #1 position? I'm ignorant on the suppressor question. And why would you want to use one on a .308 in the first place? Just curious...
I agree with you. It's a matter of overgassing causing to fast timing. Had similar issues with my 458 Socom. I'm sure the H3 should help. I'm thinking adding a flat wound spring might be necessary too but testing will tell.
And why not use a silencer in a 308? 🤔
Yes, #1 setting is for cans.
 
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The problem with '3 position' gas blocks is that it's quite possible that NONE of the 3 positions is correct for a specific need. This is where a thread adjustable gas block works better.
Most of my suppressor hosts have Adams Arms pistons installed and I've not had any problems with the OFF, Suppressor(let's call it half ON), or fully ON.
 

KneverKnew

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The problem with '3 position' gas blocks is that it's quite possible that NONE of the 3 positions is correct for a specific need. This is where a thread adjustable gas block works better.
Most of my suppressor hosts have Adams Arms pistons installed and I've not had any problems with the OFF, Suppressor(let's call it half ON), or fully ON.
Will one of those piston systems fit the SFAR?
 
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"Will one of those piston systems fit the SFAR?"
Not sure. Does the SFAR have a standard (as in: carbine, mid, or rifle) length gas port location and a .750 gas block boss?
I just bought an Adams Arms 'piston conversion kit' for Son's 6.8 SPC pistol project(10.5" barrel, carbine gas port, and .750 boss) that is advertised to work with this combination. A longer barrel should be more flexible to work with. Might be worth a contact to Adams Arms to check into the options.
I like this set-up but as I mentioned, you're stuck with on/half/off as the only options. I have 3 AR's in .223 (10.5 & 16 inch) that I use for suppressed hunting with excellent results. I've even used the OFF a few times to cut the noise a bit more and it does have it's advantages. I also have a couple of piston conversions from another brand but can't recall the name at this moment. Same principal and function just slightly different design. That design vents excess gas forward to adjust piston force rather than limiting gas to the piston.
Here's my take on how/why the short stroke piston works so well: Once the gas pressure launches the drive rod rearward, the work is done. There's no requirement or consideration of 'dwell time'--the need to maintain a significant amount of gas pressure at the gas port--as there is with the gas driven OEM AR system. On the OEM, first the gas has to fill the gas tube, then it begins to move(unlock the bolt), finally there has to be enough high pressure gas to drive the bolt rearward. This requires there be enough bore length between gas port and muzzle to maintain the gas pressure for a sufficient length of time--even though it's a micro-second.
 

KneverKnew

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I have an Aero Precision adjustable gas block. I need to order a rifle length gas tube. Any idea if the SFAR will need a standard gas tube or a straight? Hoping someone else has done this already.
 
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Try to measure the distance from gas block boss to gas tube on the SFAR and compare that to same on your 7.62x39 AR. What does the SFAR currently have?
I'm working totally blind as to the SFAR since I've never even seen one first hand. If you can compare your 'AR 47' side by side to the SFAR, you might determine similarities/differences.
 

KneverKnew

Bearcat
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I appreciate the help. For the time being I'm going to try a spare aero precision adjustable gas block I have on hand. Just need a rifle length gas tube which I just ordered. I hope this will resolve issues until I get rich enough to try the nicer options.
 

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