View Full Version : Building a Dissy from an M4 barrel
Gentlemen/ladies I hope this is not a really stupid question. I would like to build a Dissipator style AR from an M4 rifle barrel (why? I just like them). I was wondering if I just get a low profile gas block, rifle handguards and move the FSB forward, would that be enough? Drawbacks?
Thanks
http://www.google.hn/imgres?imgurl=http://img14.imageshack.us/img14/6002/dissybarrel.jpg&imgrefurl=http://www.calguns.net/calgunforum/showthread.php%3Ft%3D229600&usg=__5VvBrEosm4Ny4-NhAOfyIZT1DT4=&h=386&w=800&sz=80&hl=es&start=0&sig2=3NUkp6i1MGsoVOpXVL7CTQ&zoom=1&tbnid=qeXXK_400ARR_M:&tbnh=83&tbnw=172&ei=tLTgTILRLIP98AawyYiIDw&prev=/images%3Fq%3DAR15%2BLow%2BProfile%2BGas%2BBlock%26um%3D1%26hl%3Des%26sa%3DX%26biw%3D1440%26bih%3D837%26tbs%3Disch:1&um=1&itbs=1&iact=rc&dur=372&oei=tLTgTILRLIP98AawyYiIDw&esq=1&page=1&ndsp=35&ved=1t:429,r:7,s:0&tx=100&ty=28
http://m4carbine.net/showthread.php?t=62149
You might have already seen this thread. There is some good info here.
I have browsed through it. If I'm not mistaken the thread covers a midlenght. My plan is to do it with an M4 barrels/system.
Yes it is a midlength. There might be mention if an intermediate gas system too. But the proposal is for a midlength system. You should be able to build your upper using the same technique with your carbine. There are a bunch of great pictures and descriptions in the thread that will be helpful.
Thank You Sir, I just wanted to double check that there wasn't something "particular" to the M4 barrel.
the concern is profile dimensions.. are you saying you want to put an FSB at 12" on a 14.5" rifle? or actually tap a port at 12.5 on a 14.5" rifle? you're definitely gonna want to stick with carbine or midlength.. rifle gas on a 14.5 might be pretty hard to get right.
either way, M4 or not, probably wont make much difference. thickness at 12" on most M4 barrels is .74, a little more, a little less, depending on whose barrel.. that's not tight enough for an FSB, so you'll either need to turn down to .7495 from thicker, or turn down to .625" (lightweight).
i've never tried it, so maybe i'm missing something.. but those are my thoughts.
I'm sorry sir, you are correct I wasn't specific. It's a 16" barrel with an M4 "cut". I'm not certain to the barrel's dimensions. Please accept my apologies.
well i think we're in the realm of "something special," in that the same profile dimension limitations exist. i don't know how factory dissipaters are made, but you're likely to find that the thickness of your desired FSB plane is closer to .74" than the .7495-.75 you want to mount an FSB.
maybe somebody who's made one will pipe up.
You could shave the front sight down and put a long railed handguard on your gun with a rail mounted sight on it to get a longer sight radius if that is what you're looking for.
What are your goals with the gun. Is it just to tinker and build something unique? Sounds like it could be a fun project but there may be easier ways to get you where you want to be.
Bushmaster makes this. Part No: A BBL-16DM4A (http://www.bushmaster.com/products.asp?cat=7)
Is that a carbine length gas tube on the BN? Looks like it. I am on my phone. The BM bbl might be your best bet. Add an upper for about a $100.
arizonaranchman
11-15-10, 08:02
Is that a carbine length gas tube on the BN? Looks like it. I am on my phone. The BM bbl might be your best bet. Add an upper for about a $100.
Yes BM Dissy's use carbine lenth gas.
You could shave the front sight down and put a long railed handguard on your gun with a rail mounted sight on it to get a longer sight radius if that is what you're looking for.
What are your goals with the gun. Is it just to tinker and build something unique? Sounds like it could be a fun project but there may be easier ways to get you where you want to be.
I guess thats another way of "putting" it. I just wanted to install the full length rifle handguards, I mentioned in my OP that I've grown fond of the Dissipator setup (don't know it just makes sense to me) and instead of buying a complete Dissy upper I was wondering if I could just buy the gas block and move the FSB forward. I'm "illiterate" on ARs (learning a lot with you guys, though) but it seems it's harder than I thought.
Suwannee Tim
11-15-10, 14:20
What's a Dissy? Hold on! I got it! It's a Dissipator! Right? What's a Dissipator?
arizonaranchman
11-15-10, 14:31
What's a Dissy? Hold on! I got it! It's a Dissipator! Right? What's a Dissipator?
To my knowledge "Dissipator" is a name coined by Bushmaster for their uppers that are 16" with rifle length handguards. They use carbine length gas systems but have rifle length handguards. I'm guessing heat dissipation with the long guards is where they came up with it?
The dissipator style AR offers a lot of benefits, in my opinion:
• longer sighting radius,
• longer gas system (mid length, easier on the action & shooter),
• longer forward reach for the support hand (esp good for taller shooters),
• positions light closer to the muzzle for shadowless illumination
Set-up with a handguard like the Magpul MOE in rifle length, 16" LW barrel, and mid-length gas... I'd love to have one.
ALL good stuff.
instead of buying a complete Dissy upper I was wondering if I could just buy the gas block and move the FSB forward.
Wouldn't a clamp on FSB like the PRI (http://www.bravocompanyusa.com/PRI-Flip-Up-Front-Sight-p/pri%2005-0025%20frontsight%20%20barrel.htm) plus a handguard cap or Hahn Precision (http://hahn-precision.com/Front-Sight-Split-AGLR0103.htm) make it possible to do just that even if the barrel was closer to .74" than .75"?
I've been contemplating doing something similar as the OP, but instead maybe picking up a used BCM midlength upper to do it with.
Piece of cake, it aint hard to do at all.
I went from this...
http://i277.photobucket.com/albums/kk58/kwrangln/ar9.jpg
To this...
http://i277.photobucket.com/albums/kk58/kwrangln/ar18-1.jpg
Just chopped the FSB, added the rifle length floater tube, and added a set screw gas block (dimpled the barrel for the set screws). For a cheap rifle it runs perfectly, and still gets used even though I've built another much higher priced rifle. The one in the pics started out as a CMMG Bargain Bin rifle I picked up for $550.
:dance3: Good Job KWRANGLN!
:dance3: Good Job KWRANGLN!
Thanks. For a first time ever gunmod, it was a good exercise. That rifle is pretty much the same today, have swapped out the sights to a real Troy rear and an MI front, and went back to a collapsable stock, but it's a runner. Almost forgot, I did add a Phase 5 bolt release lever, and have a Battle Arms Designs 45 degree selector to add to it. I may make some more mods down the line, have to see.
My plan is to clone the SLR15 Commander Rifle http://www.slr15rifles.com/PhotoGallery.asp?ProductCode=SLR15Commander
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