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Posted: 8/15/2014 8:27:08 PM EDT
| So I may want to build a new dissy style upper with some parts that I already have and wanted to know if I have to buy a special FSB to fit the barrel where the diameter is smaller in front of where the gas block would normally set? This is a .750 diameter barrel with a carbine gas system. |
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I have used a YHM folding front sight and I have used a Armalite FSB and both fit without issue on the barrel forward of where the factory FSB would be.
I currently am using a PRI folding site on one of my Dissy builds but that required me removing some metal between the screws to get it to clamp down tighter. Oddly enough when you google Armalite FSB my barrel shows up. Thread here This is my PRI Dissy 
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I have used a YHM folding front sight and I have used a Armalite FSB and both fit without issue on the barrel forward of where the factory FSB would be. I currently am using a PRI folding site on one of my Dissy builds but that required me removing some metal between the screws to get it to clamp down tighter. Oddly enough when you google Armalite FSB my barrel shows up. Thread here This is my PRI Dissy http://i183.photobucket.com/albums/x282/balloo932/294a21c7-0d6c-46b2-9ad8-ef209f601957_zps15f0b91f.jpg This is one I did a couple years ago. It has a PSA 16” Hammer Forged Mid-length Dissipator upper with a .750 low profile gas block and I installed a YHM Gas Block with Front Flip Up Sight to replace the dummy A2 FSB. The front endcap is attached to the front sight base with a screw through the non-functioning, and unused, gas port of the YHM gas block. This is what allows you to secure the rifle length handguards. 
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Quoted: You would need a low profile gas block to be hidden under the handguard or rails. For the front, if you are planning not to tap and pin the foward gas block. Any set screw or screw clap gas block will do without the added cost of machining.  Here's some Dissy encouragement.  |
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The front sight block on my Dissy isn't fake.
Here's some Dissy encouragement. http://i789.photobucket.com/albums/yy180/chuckd05/20140525_234512.jpg Quoted:
Quoted:
You would need a low profile gas block to be hidden under the handguard or rails. For the front, if you are planning not to tap and pin the foward gas block. Any set screw or screw clap gas block will do without the added cost of machining.
Here's some Dissy encouragement. http://i789.photobucket.com/albums/yy180/chuckd05/20140525_234512.jpg The original Dissipator had a rifle length gas system. They basically cut down 20" barrels and opened the gas port up just a bit to account for the shorter 16" barrel. The first dissipator was the Colt Model 605. 
Bushmaster was building Dissipators with the rifle length gas system a while back. Some guys still build them this way. One day, I hope to build a 605 clone to add to my other retros. Most of the newer Dissipators are built with either a carbine gas system or mid-length gas system. The first one I built had the carbine gas system. The second on has the mid-length gas system. I do think the mid-length system is better. Very smooth. Like it was said before, if you use the shorter gas systems, you will need the low profile gas block and a FSB of some type to secure the front endcap. |
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I went a different route with attaching the "false" gas block/front sight.
I used a standard gas block/front sight and threaded the holes where the taper pins were and used allen head cup point screws (8/32 I believe). I could not find them short enough to sit flush so I had to slowly grind them down just to about the depth of the allen head opening. You can drill and tap some steel scrap to use to test the screws so you don't bugger the threads on the sight base. I also tapped the small hole at the bottom where the sling swivel would attach. Not the actual attachment point for the swivel but if you look you will see a small hole that will basically show thru to the underside of the barrel. After I was sure everything was lined up correctly I dimpled the barrel at the hole where the sling swivel mount is. I have not beat the hell out of it yet but all seems good to go. |
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Quoted:
I went a different route with attaching the "false" gas block/front sight. I used a standard gas block/front sight and threaded the holes where the taper pins were and used allen head cup point screws (8/32 I believe). I could not find them short enough to sit flush so I had to slowly grind them down just to about the depth of the allen head opening. You can drill and tap some steel scrap to use to test the screws so you don't bugger the threads on the sight base. I also tapped the small hole at the bottom where the sling swivel would attach. Not the actual attachment point for the swivel but if you look you will see a small hole that will basically show thru to the underside of the barrel. After I was sure everything was lined up correctly I dimpled the barrel at the hole where the sling swivel mount is. I have not beat the hell out of it yet but all seems good to go. I went this exact route with my Dissy's FSB and it has held up rather well to all the inadvertent abuse that I have put her through, including her falling off of a rifle rack onto concrete directly on the FSB. Dimpled the barrel and used red loctite, no issues yet. |
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Quoted:
The front sight block on my Dissy isn't fake.
Here's some Dissy encouragement. http://i789.photobucket.com/albums/yy180/chuckd05/20140525_234512.jpg Quoted:
Quoted:
You would need a low profile gas block to be hidden under the handguard or rails. For the front, if you are planning not to tap and pin the foward gas block. Any set screw or screw clap gas block will do without the added cost of machining.
Here's some Dissy encouragement. http://i789.photobucket.com/albums/yy180/chuckd05/20140525_234512.jpg Who did your furniture? Hydro or paint? it looks good. |
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Those who are using barrels that are un-notched for your non-functioning FSBs - how do you square them up to ensure your FSB is true to your rifle? Unless I have some sort of jig to get 100% alignment, it seems that the longer sight radius is moot as it won't be an aligned sight radius.
I have a dedicated .22 A2 dissy upper that was a pain to get aligned. I got it into the ballpark by resting it upside down on a flat surface and adjusted the FSB until the rear sight and front sight's "ears" were all resting on the flat surface before tightening down the set screws that were tapped into the FSB. Is there a better way to accomplish this task? |
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Quoted: Who did your furniture? Hydro or paint? it looks good. Quoted: Quoted: Quoted: You would need a low profile gas block to be hidden under the handguard or rails. For the front, if you are planning not to tap and pin the foward gas block. Any set screw or screw clap gas block will do without the added cost of machining. Here's some Dissy encouragement. http://i789.photobucket.com/albums/yy180/chuckd05/20140525_234512.jpg Who did your furniture? Hydro or paint? it looks good. Sexy weapon or swc. I think they changed names to liquid gun works now though. All in all, I think it was $300 for everything you see there. (Price included them providing the parts. CTR, BCM gunfighter MOD1 pistol grip, Pmag, Magpul MOE rifle length, and MVG.) |
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Del-Ton also has some true dissy uppers and barrels. I got one of the complete uppers a couple of weeks ago. Hope to go shoot it sunday morning. That's what mine is. I got it black friday last year. On an anderson lower, with a CMMG triggerless parts kit. I think with the GA trigger, and the paint, it's just under 1k before the ACOG. 
Shoots well though. 
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I think dissipators are cool, but the only real purpose for them is served if you have a fixed front sight post. Otherwise, you have a gas block hidden underneath a handguard, with a folding front sight one out on the end. More weight.
Then on top of it, the handguard with a rail on top(if installed) goes all the way out the 12". Seems kind of counter intuitive, how about a 13" handguard with folding sights, lighter weight, call it a day? To each his own though. |
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I think dissipators are cool, but the only real purpose for them is served if you have a fixed front sight post. Otherwise, you have a gas block hidden underneath a handguard, with a folding front sight one out on the end. More weight. Then on top of it, the handguard with a rail on top(if installed) goes all the way out the 12". Seems kind of counter intuitive, how about a 13" handguard with folding sights, lighter weight, call it a day? To each his own though. The whole thing about a Dissipator is that it uses rifle length handguards held by the forward endcap just like a standard rifle would be. Like I said in my earlier post, the originally Dissipator (Colt Model 605) used a 20" M16A1 barrel cut down to 16" while retaining the functional FSB. The gas ports were opened a little bit to compensate for the shorter barrel. The more common Dissipators of today are carbine and mid-length systems. This is why they require low profile gas block and a non-functional FSB. The FSB is used to secure the forward endcap to allow the install of the rifle length handguards. Using FF handguards does not constitute a Dissipator setup. I have several built this way along with my Dissipator. I believe that having a variety of ARs is a good thing and I have a very wide variety. |
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Those who are using barrels that are un-notched for your non-functioning FSBs - how do you square them up to ensure your FSB is true to your rifle? Unless I have some sort of jig to get 100% alignment, it seems that the longer sight radius is moot as it won't be an aligned sight radius. I have a dedicated .22 A2 dissy upper that was a pain to get aligned. I got it into the ballpark by resting it upside down on a flat surface and adjusted the FSB until the rear sight and front sight's "ears" were all resting on the flat surface before tightening down the set screws that were tapped into the FSB. Is there a better way to accomplish this task? I can just look over my carry handle and tell if it is straight. I'm getting ready to install another FSB and I'm going to take a string (a filament from inside para cord, perhaps) and tie a slip knot on one end that I will put around the front sight post and the other end I will thread through the rear sight aperture and tie it TIGHT. Now I will be able to eye-ball it and tell if it is straight easier. I've made several Dissipators. My favorite AR15 quite frankly. I just cut down 20" barrels. IIRC the gas hole needs to be .110. My favorite is a post ban 20" HBar that I had left over after the ban was lifted and I had converted my rifle to no-ban. I cut it to 16", drilled port to .110, scored a Colt A2 upper, triangular handguards, M4 stock. Sweet handling weapon! I always like to hold my hand way forwards, so even on rifle HGs my thumb touchs the FSB. |
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I was thinking about getting the DTI dissy kit, but they used a hbar profile. Another friend went with a different barrel and cut a piece of coke can to use as a shim between the barrel and gas block since the barrel usually steps down slightly in diameter where the fsb would go.
I wanted something that didn't have any play between the fsb and barrel, so I went with the Adams Arms/Voodoo 16.5" ultra lite barrel with rifle length gas. Used an Armalite FSB 
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Quoted:
The front sight block on my Dissy isn't fake.
Here's some Dissy encouragement. http://i789.photobucket.com/albums/yy180/chuckd05/20140525_234512.jpg Quoted:
Quoted:
You would need a low profile gas block to be hidden under the handguard or rails. For the front, if you are planning not to tap and pin the foward gas block. Any set screw or screw clap gas block will do without the added cost of machining.
Here's some Dissy encouragement. http://i789.photobucket.com/albums/yy180/chuckd05/20140525_234512.jpg Where/how did you get done or do that multicam job at? Lol looks awesome EDIT- found your answer further down the thread. |
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