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Posted: 5/26/2005 11:32:33 AM EDT
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What are the advantages or disadvantages of a Disapator style upper vs. a 20" upper cut down to 16" and having the gas port opened up?? The only thing I come up with is 1 less gas block on the 20" cutdown version.Am I missing something???? Reliability??? I've got HBAR Dissapator,and spare 20"HBAR's both need FSB re-drilld and reamed or pinned. |
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This is the info I dug up when I was making the decision. Cut down 20" Advantages: Lighter weight: 1 less gas block, plus it can be profiled thinner (gov't profile). Recoil: recoil impulse might be a little "smoother" with the rifle length gas system. Disadvantages: Needs the gas port opened up to be reliable Custom job can result in extra cost May be finicky about ammo choice, particulary underpowered ammo like Wolf Hidden gas block on carbine length gas system Advantages: Works just like your regular carbine Can buy from the factory exposed gas block is a "dummy" so it doesn't get as hot to burn yourself Disadvantages: Heavier: Many are HBAR, M4 profile at best, 2 gas blocks Hidden gas block may be too large to fit under some rail systems Less "unique" (?) If you plan on using a FF rail, a lo-pro midlength gas system and rail mounted front site is another option. For what it's worth (and it's worth what you're paying me for this  ), I went with the cut down 20".--Josh |
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i have had 20"ers cut back to 16" and both were a little tempramental for a SHTF rifle and for my liking. one had a match chamber so that could have been a issues as well. sold both of them. also had 2 bushmaster dissys that functioned 100% all the time. sold the the hbar version and kept the m4 version because of weight. although in hindsight, i would perfer the hbar because the balance was closer to the center of the rifle. the m4 version is nose heavy, IMO. currently have a 20" gov profile cut back to 18" and it is very smooth cycling and retained its reliability with the factory gas port. i think i like it the best. just my .02 worth of experience and opinion. |
Nah, that doesn't count! 
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FWIW, properly equipped, chopping a 20" barrel isn't very hard at all. For those who don't have the equipment, the midlength gas system works also and would be very simple, but for the "true" Dissy look, you are still installing a second gas block forward of your midlength gas block. That's what Underdog75 did on his "Dissergy". He used a midlength barrel with a low profile gas block and a PRI flip sight base forward of that. It was a pretty sweet build. See pic below. 
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I say carbine length with an installed 9mm buffer for the true Dissy look/concept: (Just for clarification, when I say “true Dissy look/concept” I’m talking about any fixed front sight, ahead of any rifle length handguards installed on a carbine length barrel.)   If not going for the “true Dissy look/concept” I’d like to do an upper build like Underdog75’s, but go with the rail mounted fixed LMT front sight instead… I’d end up with the fixed LMT rear sight as well. (What can I say; I’m a fixed sight kind of guy. ) |
That's pretty much what I was thinking also. I'd say that a midlength barrel with a rifle length FF tube and no barrel mounted front sight is Dissy-like but not quite Dissy. YMMV. |
so you pawned them on someone else? |
oh for christ sake, did i say i fucked someone over? and if i did do you really think i would post that info here? so, no pawning was involved. both sales were straight forward and the buyers knew what they were getting. thanks for your concern. now on to the topic at hand,, here is the M4 profile bushmaster dissy,, 
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Of course, I mentioned it to you once already via e-mail, but I'd personally go with the mid-length as has already been mentioned. In fact, I'd look at the Talon/Sabre Defense mid-length deal for $245. An extra advantage of the mid-length gas system over a standard carbine is that the extra 2" of barrel behind the gas block equals 2" inches of profiled barrel! According to the MD AR15 CDROM technical info, a 14.5" M4 weighs 29.5 ounces, while a 16" government profile middie weighs 30.5! That's 1.5" LONGER and only 1 ounce heavier! Of course, that same logic DOES make a cut 20" even lighter, but requires no work or extra cost to have done. Then there's the Bushmaster Superlight barrel that would make the lightest of all, save a chopped Colt A1  I will be converting my RRA mid-length barrel into a Dissipator as soon as I sell my 18.5" barrel and buy a superlight to make a carbine
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the only problem in chopping a colt SP1 skinny barrel is that the factory has a slight flare to the muzzle were the threads are. once you chop in down there is less barrel diameter than the original and the lock washers can sometimes be a little sloppy. |
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While you guys are all planning these Dissys with carbine or mid-length gas blocks and a second front sight, don't forget that Armalite makes a clamp-on front sight base that (although I have no first hand experience) SHOULD work just as well as the PRI as far as clamping onto the slightly smaller diameter of the carbine barrel out near the muzzle... You don't HAVE to have a Bushmaster Dissipator barrel to make a "true" Dissy... in fact, you may have your next barrel in your safe already I haven't decided yet, but I'll do either PRI or Troy. |
Crush washers are perfect for this application. |
ah, excellent idea. i have never used the crush washers but have seen them and know of their purpose. thanks for the tip! |
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