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Posted: 7/22/2006 7:40:35 AM EDT
Anyone know why i couldn't easily convert a dissy barrel to a mid-length?
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You cannot easily do it because your barrel likely has a carbine length gas system. You would have to drill a new gas port of the right diameter, and you'd still have tons leaking out the old hole. I suppose you could go for the midlength look by installing a new FSB where a midlength one would go and you could keep your current gas set up. |
Randall at AR15 Barrels might be able to help you, but he might also tell you it would be easier and more reliable to simply buy a new barrel. You would have to relocate both the gas port and the fsb. EDIT: It also depends on what kind of gas system you have, rifle or carbine. If you have a carbine gas system it would be as simple as putting a low-profile gas block on and putting a rail over it. The above advice was assuming it had a rifle gas system. |
Bushmaster dissipator barrels have a 0.750" gas block at the carbine location hidden under rifle length handguards. Then they have a FSB that's bored 0.720" to slide on to the barrel where they normally is NOT a rifle located FSB. As the barrel is profiled down to 0.720" forward of the carbine port, it's not easily possible to re-locate and mount a gas block at mid-length. You could feasibly machine the barrel smooth to say 0.700" and add a gas port there. Then bore out a YHM 0.625" specter gas block to 0.700" and mount it. Then it's a matter of plugging the old gas port. I will mirror what ZootTX said and tell you to just buy a barrel that's setup like you want. I have multi-role CMMG barrels in stock that I could setup as a mid-length dissipator for you. |
You can have a dissy setup with a carbine or mid or rifle length gas system. Bushmaster stocks a dissy setup with a carbine GS. You can make a dissy yourself. I once had one with a midlength GS/16" barrel and made it a dissy simply by using a low profile gas block and a free floating tube of rifle length. Some people have a made a dissy by taking a traditional 20" rifle and chopping the end of the barrel off and having it recrowned. |
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Learn something every day! I was under the impression that a dissipator setup was by definition a 16" barrel, with a carbine GS, but with rifle length handguards and rifle-length FSB (with a low profile gas block under the handguards). Would a 20 in. rifle barrel cut down to 16 in. operate properly with the gas port that close to the muzzle? (And would this really be a dissy, or just look like one)? |
That would be a correct description of a BUSHMASTER Dissipator.
Cut down rifle barrels can be made to run, but usually not as reliably as barrels with a more proper gas system arrangement. I recommend staying to at least 17" for best reliability with a rifle gas system. |
Depends on how big the port is now. MOST barrels WILL need the gas port opened up when going to 17" I just cut one to 18" and the customer reports needing to open the gas port after he test fired it. |
It's all good because I'm going to have you do it for me! 
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| I've had relatively good luck chopping 20" rifle barrels to 16.5" with a gas port of 0.105-0.110". This setup runs nearly 100% with all types of ammo, except underpowered ammo and crap remanufactured ammo. I've got another in the works for me, but so many things get in the way. |
Point fingers and name names... WOLF is the problem. That's why I suggest 17", just a little more gas getting into the system. As you mentioned, 16.5" is not too bad, but all the way back to 16" and it definetly gets a little less reliable. |
That would be a correct description of a BUSHMASTER Dissipator. Who else makes dissipator barrels/uppers? |
I think "Model 1" Makes them. |
Ya, didn't want to turn this into a Wolf pissing contest, but yes, Wolf gives me the most problems with any custom or off the wall build. Facts are facts. FWIW, Ultramax was another ammo that gives me sporadic fits. |
Does this mean we're gonna have Nazis running around on ARF.com correcting the use of "Dissipator" just like the "M4" Nazis or the "Colt vs. Colt's" Nazis? Please, let's not. |
Yes, because too many fucktards use the term Dissy to describe all sorts of shit that has nothing to do with the Bushmaster Dissipator or anything Dissipator styled. That and the fucking term dissy sounds totaly fucking gay. |
I've noticed that people who make statements like: "I've noticed that people who use foul language alot tend to do so because they don't have anything important to say, but want to sound like they do. they use shock as a replacement for substance." Are more than likely to be whining liberals. |
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no you don't, you're just being a smartass, and not a very witty one either. But at least your response is not rated R. Since Bushmaster has yet to trademark the tern "dissipator" like Colt tried to to with M4, you have no moral authority to insist the term applies exclusively to the Bushmaster design. And "yelling" about it and using foul language is nothing more than a bullying tactic to force your opinion on others. Why you be hatin'? |
It's not just the amount of barrel beyond the gas port that determines port size. It's also the pressure of the gas occupying the barrel forward of the port and the velocity of the projectile (dwell time) as it passes between the gas port and muzzle. For reference, here is my port pressure graphic:  Your 11.5" barrel is probably around 0.070" and a 17" barrel made on a rifle gas system would run around 0.100" |
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I don't get this thread.... It woudl be EASY to convert a Dissy to a Midlength... WHO NEEDS TO CHANGE THE GAS PORT LOCATION UNLESS IT DOES NOT RUN? Just take the junk off the barrel including the current Front Sight base and add a Mid-Length Free Float tube. If you want a new Front sight base at the end of the Mid Length Float tube then you will need to have someone mill it but bot really a big deal... I would just plug the original holes from the FSB with some cut off taper pins and go for it... Now, it would be easier and cheaper to likely sell what you have and but another upper used but you aksed how hard it would be... My answer... NOT THAT HARD! |
Bla bla bla. Bushmaster makes the Dissipator. End of story. There is no such thing as a "dissy". Using the term dissy makes one sound like a limp-wristed slack jawed faggot. Take your holier than thou attitude..... Again, for the people who can't comprehend: Bushmaster makes the Dissipator. There is no such thing as a dissy. Calling a Dissipator styled rifle a dissipator styled rifle is perfectly acceptable. Plus, if you read all of the crap posted about dissy this and dissy that it IS all crap. Why do people have to fuck around with the faggoty names. There is only ONE Dissipator, and that's the Bushmaster Dissipator. What makes an AR15 a dissipator styled rifle is a carbine gas system and a full length rifle front sight.  Bushmaster M4 Dissipator  Bushmaster HB Dissipator Do you go into a Chevy dealeship and say "I want a Ford styled trucky?" This is not my opinion either, this is fact: IF it does not have a carbine length (16 inches) gas system and a full rifle length (20 inches) front sight then it's not a Dissipator or a dissipator styled rifle. Markm hates Oly, I hate the term "dissy". |
Define EASY. Easy is relative. I have a lathe, it's easy... Joe Schmoe does not have a lathe, not so easy... It's not so much that they NEED to change the gas system, it's that every armchair commando here on arfcom says you HAVE to have a mid-length gas system so the sheeple WANT a mid-length dissipator now... Also, I don't think people want mid-length handguards if they have a dissipator. I think they are talking about still having the rifle-length FSB and having a mid-length hidden gas block like this:  I already mentioned the issue of barrel diameters and the solution is to open up a 0.625" gas block to around 0.700" and skim the barrel down to 0.700". Of couse the easy solution is to sell the barrel you have now and buy the one that's just like you want... |
Model "1" Dissipator Rifle Kits and in case you don't wanna click on the link.  Since they didn't trademark it your statement is incorrect or at best is a matter of opinion. |
Neither of those ads are for "dissys".  Both of those ads are for 16 inch barrels with carbine length gas systems and a full length rifle front sight, which, again, is acceptable, because of the simple fact that they are based on the Bushmaster Dissipator. Fact: ONLY Bushmaster makes the Dissipator rifle. Fact: Anyone else who makes a Dissipator styled rifle and calls it a Dissipator is making a copy/clone, probably because they could not come up with a "cool" enough name themselves. Fact: There is no such rifle as a dissy. Fact: Dissy sound totaly fucking gay. Fact: In this thread (like so many others) most people are clueless as to what a dissipator rifle is. Fuck it, instead of calling them dissys call them elimys. Olympic Eliminator, get it. 
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And because this site is AR15.com, we are only allowed to talk about COLT AR15's because a term is never allowed to become generic, even if it makes explaining something easier. Please stop calling anything other than a Colt-manufactured rifle an AR or AR15, even if it means you have to type an extra paragraph to discribe the gun. FACT: getting worked up because people call 16" barreled uppers with a rifle-length sight-radius "dissipators", even though they aren't manufactured by Bushmaster is uber, UBER ghey. When someone says, "I want to build a dissipator", we all know very well that they don't mean they want to apply for a job at Bushmaster, interview, and be hired just so they can assemble Dissipator uppers for Bushmaster in Maine. Just to prove my point, I'm making a dissy upper right now, and not giving Bushmaster any royalties. Once complete, I'm having my gunsmith laser-etch the receiver with "Dissipator". Disclaimer: Although I used the term "dissy" here, anyone who questions my sexuality can feel free to ask my wife. |
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You history of the AR15 is lacking. This site is called AR15.com and we should only be talking about ARMALITE AR15's because eveything else is just a copy.
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First I'll apologize for using the 5-letter word "dissy" in the title of this thread - I didn't realize how politically incorrect this was and how offensive this word is to some people. Secondly, I'll apologize for getting back to the original theme of this thread.I just received the barrel in question (a used barrel I bought on the EE), and I now see that converting the carbine-length gas system to mid-length would be very easy. This is a Bushy (hmmm - is that a faggoty word?) Hbar dissipator, with a 0.750 diameter from the carbine gas port out to the FSB. All I have to do is plug the existing gas port (this could be done several ways, but I suspect that JB Weld would work just fine), drill a new gas where I want it, and relocate the low-profile gas block. I could then use standard rifle-length handguards (pure dissapator "look") or use a free-float handguard. Only problem - I see from one of Randall's posts that wanting to convert a carbine-length gas system to mid-length makes me a "sheeple" (I wonder if this word is offensive to sheep??). Nothing worse than faggoty sheeple running around with dissies! From what I've read here on arfcom, I thought mid-length gas systems were an improvement over carbine-length. Wrong??
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Faggoty Sheeple running around with Dissy's could potentially be a problem but no worse than Zombies so thank goodness you have an EBR to kill zombies with! Are you sure that your barrel is 0.750" forward of the gas block? The one I measured recently was 0.720". This is what precludes you from simply plugging the old hole and drilling a new one 2" forward. By the way, carbine to mid length is exactly 2.000" movement of the gas port and gas block seat. JB Weld is NOT going to hold the 34,000 PSI gas pressure. Tap the hole for a setscrew at the minimum. I make a plug and then weld over the top of the plug when I do this job. Mid-length is a better setup on a 16" barrel. My sheeple comment is to describe people that want mid-lengths JUST because it's cool, not because they understand the technical reasons for it. |
All else being equal, it will not hammer the rifle as hard during reload. Here is some fact/propaganda: www.defensereview.com/modules.php?name=News&file=article&sid=360 |
| Randall - My barrel DOES have a slight stepdown forward of the gas block area, but I still measure 0.745 two inches forward. I've got 2 low-profile gas blocks (one one-piece with 2 set screws and one two-piece with 4 allen screws) which work fine with this diameter. Appreciate the tip re the JB Weld - I was also thinking of tapping and screwing. Question - can I cut down a rifle-length gas tube? Or would this not work? |
0.745" is not so bad as the 0.720 I measured... I would use the YHM block, I think it will seal better by clamping with 4 screws than a setscrew block would. Just buy a proper mid-length gas tube. It's really not worth fooling with shortening a rifle tube for the $15 savings. |
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