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Posted: 3/9/2009 3:11:03 PM EDT
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Ok, so im doing my first build and am a little confused as to where these gas blocks come into play. Ive been using the ar15 diagram (see here http://www.ar15.com/content/guides/parts/ ) and dont see any mention of gas blocks... so when do they get used and why?
For what its worth im building an M4 wanna be with a free float 7" DD rail and a 16" M4 profile barrel with an ARMS front flip sight. |
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I'm not going to go into great detail because I don't know all the proper terms, I'm sure someone will. The gas block is used to transfer gas to the gas tube which then transfers gas to your gas key on the bolt carrier which cycles a new round. I know someone has a .gif of the whole operation this will help.
there is a hole in your barrel under the gas block which is how the gas gets to the gas block to begin with. This is the system used to cycle new rounds and is used instead of a piston design in which no actual gas enters your receiver. Hope that helps. |
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The gas block mounts on the barrel over a hole in the top of the barrel called a gas port. The block then has a hole that the gas tube goes in and then runs back into the upper receiver.
See the black block above the barrel. Gas tube (not pictured) inserts into that and runs back along the barrel into the upper receiver. 
-Foxxz |
| yes it has an integral gas block, see the description here http://www.tactical-life.com/online/products/arms-silhouette-folding-front-sight/?right=related |
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I think your confusing something here. The early M-16/AR-15 used a Front Sight Base (FSB), I guess to keep it light, simple and cheap, they combined a lot of things into 2 pieces mounted together at one point on the barrel. The Bayonet Lug, the adjustable front sight and the gas block with the end cap for mounting hand guards.
In the last couple of years they started to come up with all different accessories and configurations, including free floating fore arms that ditch the old handgaurds and can even extend past where the front sight mounts, and instead used a front sight mounted on the forearm. Thus low profile gas blocks that just mount on the barrel and port the gas to the gas tube back to the BCG. No matter how you configure the weapon, you have to have a MANIFOLD/Block that mounts over the gas port on the barrel and connects up the gas tube. In your case you got combo unit, that is a lot like a fold up version of the early FSB. I'm still waiting on my back-ordered Troy TRX 11" battle rail, that will extend over the gas port on my barrel. I have a troy low profile gas block to fit underneath the forearm and YHM flip up front sight to mount on the picatiny rail on the top of the forearm. I even got bayonet lug that mounts on the barrel so I can mount my OKC3S bayonet. |
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Quoted:
I think your confusing something here. The early M-16/AR-15 used a Front Sight Base (FSB), I guess to keep it light, simple and cheap, they combined a lot of things into 2 pieces mounted together at one point on the barrel. The Bayonet Lug, the adjustable front sight and the gas block with the end cap for mounting hand guards. In the last couple of years they started to come up with all different accessories and configurations, including free floating fore arms that ditch the old handgaurds and can even extend past where the front sight mounts, and instead used a front sight mounted on the forearm. Thus low profile gas blocks that just mount on the barrel and port the gas to the gas tube back to the BCG. No matter how you configure the weapon, you have to have a MANIFOLD/Block that mounts over the gas port on the barrel and connects up the gas tube. In your case you got combo unit, that is a lot like a fold up version of the early FSB. I'm still waiting on my back-ordered Troy TRX 11" battle rail, that will extend over the gas port on my barrel. I have a troy low profile gas block to fit underneath the forearm and YHM flip up front sight to mount on the picatiny rail on the top of the forearm. I even got bayonet lug that mounts on the barrel so I can mount my OKC3S bayonet. So if im reading this correctly i will need a manifold block in ADDITION to the front sight with the integrated block? Sorry if i keep making you guys beat a dead horse, im just trying to figure this out in my head... |
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No, you've got everything you need in the ARMS silhouette flip up front sight and integrated gas block.
Sorry, I probably confused you throwing in the term MANIFOLD, technically the term for something like this is a MANIFOLD, but its called GAS BLOCK in the AR-15/M-16 community and literature. You have a hole drilled in the barrel, its the gas port that provides the pressure to cycle the weapon by venting off a little bit of the pressure in the barrel as the bullet passes the hole in the barrel. That gas has to get back to the bolt carrier group (BCG), its carried by the gas tube back to the BCG. You have to connect up the gas tube with the port in the barrel, its the gas block that does that. The gas block clamps over the barrel and seals up around the port, there is a passage in the block leading to the gas tube that also inserts in the block and is held in place with a roll pin. I was just pointing out that there are all sorts of gas blocks, some have sights on them, some don't and they are as small as possible to fit under forearms, etc. |
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Quoted:
I think your confusing something here. The early M-16/AR-15 used a Front Sight Base (FSB), I guess to keep it light, simple and cheap, they combined a lot of things into 2 pieces mounted together at one point on the barrel. The Bayonet Lug, the adjustable front sight and the gas block with the end cap for mounting hand guards. In the last couple of years they started to come up with all different accessories and configurations, including free floating fore arms that ditch the old handgaurds and can even extend past where the front sight mounts, and instead used a front sight mounted on the forearm. Thus low profile gas blocks that just mount on the barrel and port the gas to the gas tube back to the BCG. No matter how you configure the weapon, you have to have a MANIFOLD/Block that mounts over the gas port on the barrel and connects up the gas tube. In your case you got combo unit, that is a lot like a fold up version of the early FSB. I'm still waiting on my back-ordered Troy TRX 11" battle rail, that will extend over the gas port on my barrel. I have a troy low profile gas block to fit underneath the forearm and YHM flip up front sight to mount on the picatiny rail on the top of the forearm. I even got bayonet lug that mounts on the barrel so I can mount my OKC3S bayonet. Is there any truth to the rumor that an aftermarket gas block won't seal like the factory one? |
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Quoted:
Is there any truth to the rumor that an aftermarket gas block won't seal like the factory one? Sometimes. It is more of a problem with polished stainless barrels. I have corrected the problem by using Green Lok-Tite around the gas port to achieve a proper seal. It's pretty simple. Flow the Green Lok-Tite around the gas port, slide the gas block in place & tighten it down. Allow it to set up for at least 24hrs & you should be good to go. |
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