Help me build a Dissipator upper
- Thread starter nitesite
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SHOOTER13
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Just for those who may not know the term...
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A Dissipator is an attempt at a "best of both worlds" AR carbine, combining the long sight radius of the full-length M16A2 with the shorter barrel of some of the shorter carbines. This combination would allow the most effective use of the iron sights for a carbine with such a short barrel, and may be preferred if the carbine is going to be used primarily with iron sights. Earlier conversions sometimes suffered from reliability problems due to the close proximity of the gas port to the muzzle, which throws the timing of the weapon's gas system off and makes it especially sensitive to gas port diameter and port pressure variables introduced by the ammunition.
One solution was to use the front sight tower/gas block in its regular, long sight radius position as for the M16, and then fit a second, "shaved" gas block at the normal position for the carbine-length barrels such as the M4 or CAR-15. This second gas block is completely covered by the standard full-length M16A2 handguards, which may be used without further modification. However, some aftermarket rail systems may require minor modifications in order to be properly fitted. Dissipator barrels are available in heavy, fluted, and "M4" configurations, depending on the weight and balance characteristics required by the user.
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A Dissipator is an attempt at a "best of both worlds" AR carbine, combining the long sight radius of the full-length M16A2 with the shorter barrel of some of the shorter carbines. This combination would allow the most effective use of the iron sights for a carbine with such a short barrel, and may be preferred if the carbine is going to be used primarily with iron sights. Earlier conversions sometimes suffered from reliability problems due to the close proximity of the gas port to the muzzle, which throws the timing of the weapon's gas system off and makes it especially sensitive to gas port diameter and port pressure variables introduced by the ammunition.
One solution was to use the front sight tower/gas block in its regular, long sight radius position as for the M16, and then fit a second, "shaved" gas block at the normal position for the carbine-length barrels such as the M4 or CAR-15. This second gas block is completely covered by the standard full-length M16A2 handguards, which may be used without further modification. However, some aftermarket rail systems may require minor modifications in order to be properly fitted. Dissipator barrels are available in heavy, fluted, and "M4" configurations, depending on the weight and balance characteristics required by the user.
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What is the benefit of the shorter gas system vs. simply running it all the way forward to the sight post? It seems that cycling/timing issues are more of a concern for full and select fire rifles than for semi-autos. Just curious...
Nitesite A2 as in A2 carry handle, or do you want a non flat top upper reciever A3? What grain bullets you shooting. I would get a quality upper reciever, you may opt to get one with the forward assist installed. Mega Machine is good, BCM is Good, DTI is good, I would get the best deal I could find. Palmetto State Armory has some smoking deals. Check around, sometimes can find them below $100.00.
Get a duty rated properly staked bolt and carrier group, I use Bravo Company USA, http://www.bravocompanyusa.com/BCM-Bolt ... o%20mp.htm. I have had very good luck with them, I have used a few others, but I use thesein My personal rifles.
Rear flip up sight if a flat top upper is used A.R.M.S 40LP, if an A2 is used, well the sight is there. The barrel, is the next thing, I like 1:7 twist chrome lined barrles. Nothing wrong with 1:9 twist, I just like the 1:7. I like a heavier contour barrel. Oh and a charging handle.
Be sure if you are going with the Flat top upper, that the front sight post assembly is marked "F" there is a difference between an A2 front sight assembly, and the flat tops assembly. Your going to need a gas tube, roll pin, crush washer, and flash supressor. Add the fore end of your choice, and your on your way.
Get a duty rated properly staked bolt and carrier group, I use Bravo Company USA, http://www.bravocompanyusa.com/BCM-Bolt ... o%20mp.htm. I have had very good luck with them, I have used a few others, but I use thesein My personal rifles.
Rear flip up sight if a flat top upper is used A.R.M.S 40LP, if an A2 is used, well the sight is there. The barrel, is the next thing, I like 1:7 twist chrome lined barrles. Nothing wrong with 1:9 twist, I just like the 1:7. I like a heavier contour barrel. Oh and a charging handle.
Be sure if you are going with the Flat top upper, that the front sight post assembly is marked "F" there is a difference between an A2 front sight assembly, and the flat tops assembly. Your going to need a gas tube, roll pin, crush washer, and flash supressor. Add the fore end of your choice, and your on your way.
Flat top upper or A3. http://www.del-ton.com/AR_15_Upper_p/ur1022.htm
A2 Upper. http://www.del-ton.com/AR_15_Upper_p/ur1019.htm
Barrels, Read the fine print, it appears this one is NOT chrome lined. They will state if it is chrome lined. http://www.del-ton.com/Del_Ton_Barrels_p/bl1017.htm
This one is pricey, but has the extras, (This is what I would use) http://cmmginc.secure-mall.com/item/16- ... arrel-1764
Another option 5th one down, http://www.bushmaster.com/products.asp?cat=7
A2 Upper. http://www.del-ton.com/AR_15_Upper_p/ur1019.htm
Barrels, Read the fine print, it appears this one is NOT chrome lined. They will state if it is chrome lined. http://www.del-ton.com/Del_Ton_Barrels_p/bl1017.htm
This one is pricey, but has the extras, (This is what I would use) http://cmmginc.secure-mall.com/item/16- ... arrel-1764
Another option 5th one down, http://www.bushmaster.com/products.asp?cat=7
nitesite said:
just curious, but are you set on the A2 upper? You are talking about the upper with the built-in handle. The reason I ask, it makes attaching optics a bit 'weird'. Another option, if you need to have the 'handle' look, use an A3 with detachable handle. That way, you can remove the handle and still have a flat-top rail to attach optics of choice.
Is this upper something you want to totally build from scratch? As in, you are going to buy all the parts separately and assemble it all yourself? Again, the reason I ask is to get an idea of experience level, so as to not offend you by suggesting something too involved or too simple.
I would also suggest going to a mid-length gas system under the hand guards or rail system. Then use a standard A2 front sight (by itself) up front - if that's the front sight that you like.
Bushmaster sells a complete A2 Dissipator upper (assembled) for around $500 and change. PK Firearms has the Bushy, also an assortment of Rock River mid-length uppers (assembled) that you could use. http://www.pkfirearms.com/Rock_River_Arms_Barreled_Uppers/57/c
Aim Surplus has a good selection of SPIKES uppers that you could use to get a start on this build, too. http://www.aimsurplus.com/catalog.aspx?groupid=368&name=Upper+Receivers and other AR parts
http://www.aimsurplus.com/?Accessories Webstore
Del-ton also makes a dissipator upper http://www.del-ton.com/Custom_Upper_p/cu112.htm
Here's a link to someone who used a Model 1 dissipator kit for a build http://www.majorpandemic.com/2011/09/model-1-sales-556-dissipator-upper-ar.html
If you want to build it all from parts, here's a good price on a barrel:
http://palmettostatearmory.com/2542.php
Thanks for all the replies and suggestions, guys.
mister_e, I guess I could go with an A3 and removeable carry handle (I have one laying around). And yes, I do like the fixed A2 front sight if and when I start the build.
I've never done a build before and don't have any dedicated tools for assembling an upper.
Saltmarsh, I appreciate the links you provided and mister_e the links you posted are equally good! My plan is to get just the parts needed to reconfigure a complete DCM upper which I already own so as to keep the cost down.
mister_e, I guess I could go with an A3 and removeable carry handle (I have one laying around). And yes, I do like the fixed A2 front sight if and when I start the build.
I've never done a build before and don't have any dedicated tools for assembling an upper.
Saltmarsh, I appreciate the links you provided and mister_e the links you posted are equally good! My plan is to get just the parts needed to reconfigure a complete DCM upper which I already own so as to keep the cost down.
My current upper build is similar to what you're looking at, but it's not a dissipator. I'm utilizing a midlength gas system with a low-prifile gas block tucked under a longer quad-rail forend and I'll be using Troy flip-down front and rear sights. Like I said it's not a dissipator, but my front sight will be further forward than a standard midlength with an A2 sight post.
nitesite said:
With that in mind, the easiest way to get there might be to buy an assembled upper (either carbine or mid-length), then shave the A2 sight down to fit under the handguards or rail of choice. This doesn't alter anything other than the original A2 sight. Then buy another A2 sight and pin it on the barrel.
OR...like Lazy has done, shave the original sight to clear, install a rail system, and add a fold down sight to the top of the rail.
If you are trying to keep the Bushy Dissipator look, you will probably want to add rifle-length handguards and another A2 sight.
You can also install rifle-length rails (free float or non-free float), install a fold down sight and still have the Dissipator look.
For weight saving, going with the regular rifle length handguards might save you a little weight. UNLESS...you have the extra coin, and spend it on some of the new Uber-light rail tubes like the Daniel Defense Omega series or the Troy tubes. There are also some new tubes out that are carbon-fiber.
If you do some shopping, you can find a good upper, with the barrel you like (material, twist ratio, fluted or not, muzzle break/flash hider, etc) then start modifying it. That is the best part of the AR platform, there is virtually nothing you CAN'T do, to modify it into something YOU like.
As for special tools - about the only thing you might need is maybe a Dremel to cut off the A2 sight and grind it smooth (and maybe to cut the Delta ring off - if you use a Midwest Industries rail system - http://www.weaponevolution.com/foru...-Industries-Rail-install-and-pictorial-review), and some punches to install another A2 sight.
Yes, you can buy a lot of 'special' or 'right-tool-for-the-job' type tools, and if you are going to be assembling more than just one AR, I would probably suggest investing in some. But for the most part, you can assemble a complete AR with most tools that you already have. You just have to take your time, and be careful.