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-   -   Calguns Everything about the Dissipator thread. pics, discussion, tech (https://www.calguns.net/calgunforum/showthread.php?t=493277)

FatalKitty 10-26-2011 9:21 PM

Calguns Everything about the Dissipator thread. pics, discussion, tech
 
This is a thread for discussion and sharing of the Dissipator type Ar-15
One place for information, history, and photos!


For the purpose of this thread, the term "dissipator" will refer to the design concept and not the specific model name. I would rather not argue semantics or get into the "who invented what" debate please. Let's just say a dissipator is a 16" barrel with the front sight post in the rifle length position.




The Colt Model 605A

Quote:

The Model 605 was the first attempt by Colt to produce a "Carbine" style AR15/M16. The two Models offered were the Model 605A which had a 3-Way Fire Control Group (Safe, Semi, Auto), and the 605B which had a 4-Way Fire Control Group (Safe, Semi, Burst, Auto) The barrel was cutoff just past the Front Sight Base, the Bayonet Lug was removed, and the Flashhider was reattached giving the "Carbine" an overall length of approx 34 inches. This model was produced in very limited numbers and never saw any wide scale use in the field by Military Forces due to its unreliable operation
http://pullig.dyndns.org/retroblackr...rbGde/605.html

This is the original concept as it relates to the M16, Basically just an ad hoc Carbine suited for mounted troops. It didn't last long but can be spotted in Vietnam era photos. While the idea was a sound one, it was poorly executed and later scraped. Other variants with shorter gas systems eventually replaced this design due to their reliably as a result of an increase in dwell time.

http://farm7.static.flickr.com/6036/...e1580dfe2d.jpg
The Colt 605a - Basically an M16 with the barrel cut down to 15 inches.



The Concept

To understand what a Dissipator is, we must first examine the purpose of such a design.

1. In close quarters or situations where individuals are mounted, a shorter barrel is desired. Shorter barrels allow freedom of movement and reduced weight while sacrificing velocity. The drop in velocity from a 20 inch barrel down to a 16 inch barrel is about 200 feet per second using the same gas system.

2. Longer sight radius allows for more precise alignment of the front and rear post. On a rifle where Iron sights are used (as is the case in an A2 rifle) the longer the sight radius the more accurate the shooter.

Now one could easily overcome this compromise by using a low profile gas block and switching to a free flowing rail system that allows a rail mounted front sight to be positioned further down the barrel. This design significantly modifies the rifle with new parts that are often expensive, heavier, use proprietary mounting systems, and is not as tough as a standard A2 sight post.
On a rifle with an A2 style front sight post that is also the gas block, in order to get the best of both worlds, you have to use a rifle length gas system (12inch) while using a shorter carbine length barrel. This creates a number of problems.
The first being gas delivery. The AR-15 requires a reliable gas charge from a spent cartridge. As the bullet travels down the barrel, the gas pressure building up behind it is directed through a hole in the barrel, through the gas block and front sight assembly, down a gas tube and then into the bolt carrier where it cycles the bolt and carrier to complete the action.
When you have a shorter barrel, the gas has less time to build pressure and travel down the tube and into the bolt carrier assembly. This is what is referred to as "dwell" time. The bullet in the barrel holds the gas in place behind it as it travels. The shorter design of 16" barrel simply does not allow for sufficient gas delivery and reliability is sacrificed.

http://farm7.static.flickr.com/6092/...1028b53063.jpg
Chart showing the different velocities achieve using different gas systems and barrel lengths.

http://farm7.static.flickr.com/6055/...6959712be8.jpg
Comparison of the dissipator design with the most common gas systems and barrel lengths



The Bushmaster Dissipator

Fast forward many years after Vietnam and welcome to the civilian AR-15.

Quote:

The Bushmaster 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 (16.1"/406mm) 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. Similar modifications have been accomplished in the past by other manufacturers and by depot-level modification, but these 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. Bushmaster's 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.
Bushmaster creates what they call the "dissipator" model for people looking for a reliable yet effective short barrel/long radius rifle.
The design uses a carbine gas system with a gas block hidden under the rifle length hardguards. Up front is a "dummy" A2 sight block that is pinned to the barrel in the rifle length position. The result is a reliably operating rifle with a longer sight radius.
Bushmaster still offers their original dissipator concept upper complete with bcg for $605 (part number BURA2B 16D)

http://farm7.static.flickr.com/6031/...b4dde16f00.jpg
Photo showing the Bushmaster Dissipator with second gas block hidden under the handguards



The Other Designs

The original design with a rifle length gas system and shorter barrel still exists today. Reliability is enhanced by enlarging the gas port in the barrel and thus negating the need for a second slave block that not only creates additional heat but also weight.
Many SPRs use a shorter 18 inch barrel with a rifle gas system, this is considered to be the most reliable and is favored by 3 gunners and competition shooters.



The dissipator in MOVIES

A Marine aims his rifle during the Embassy scene in The Bourne Identity
http://farm7.static.flickr.com/6092/...667fb9b3ec.jpg



FatalKitty 10-26-2011 9:21 PM

WHERE TO BUY
DPMS at JSE - http://www.jsesurplus.com/ar1516barr...eight-1-1.aspx
DTI at JSE - http://www.jsesurplus.com/ar1516barr...ght-1-1-1.aspx
(from what i understand, Delton makes these for DPMS or the other way around, they are the same quality, and are actually very good for the price)
CMMG CHF barrels in several profiles and configs (including slave block type dissy and rifle dissy) http://cmmginc.secure-mall.com/categ...HF-Barrels-207
AIM Surplus complete upper http://www.aimsurplus.com/product.as...er&groupid=368
PSA "mock" HF mid length upper (complete) http://palmettostatearmory.com/8974.php
PSA "mock" CL mid length upper (complete) http://palmettostatearmory.com/2537.php
PSA also has Carbine gas system uppers but are out of stock (bottom of page) http://palmettostatearmory.com/ar-complete-uppers.php
Addax Tactical has recently jumped into the fray with both a midlength/mock dissy and a full rifle length gas system http://www.addaxtactical.com/store/p...LY-57p5557.htm

I will be updating this thread with new ideas, videos and photos to come :)


HOW TO build your own Dissipator: method 1

http://farm7.static.flickr.com/6224/...b4f4e0ae84.jpg

The advantage of having a true rifle length gas system is the recoil felt. One can argue that the 5.56 does not have much recoil and would be correct. The cycling action actually causes as much recoil as the round down the chamber does. This is only exacerbated by a shorter gas system, allowing a high pressure quick pulse of gas down the tube into the BCG rocketing it back into the stock and shooter. With a rifle length gas system the felt recoil is lower. When looking at a rifle where Iron Sights are a priority - the least amount of recoil possible is desirable.

You have a couple options. Either have a gunsmith cut down and rethread (if muzzle device is desired) a standard 20" barrel, or find a 16" barrel that already uses a rifle gas port.
DPSM, CMMG, and others already make these barrels and they make them with enlarged gas ports for reliability.
I personally have owned the DPMS version, it will cycle wolf ammo with a spikes ST2 buffer. You can trust this design
both jsesurplus and midwayusa sell the DMPS version when they have them in stock (for as little as I see these rifles in the real world, the barrels sure do sell out quick)

This method is simple because it only involves replacing the barrel and handguards - a job anyone with the tools can do.

Parts required:
1) New barrel
2) Rifle length (12") handguards of your choice
3) Rifle length gas tube

Instructions:
1) Remove carbine hand guards.
2) Secure upper.
3) Remove gas tube.
4) Remove old barrel from upper.
------------------------------
5) Install new barrel, torque to proper specs
6) Install new gas tube
7) Install handguards


RESULT:

http://farm7.staticflickr.com/6120/6...c3321c7fb6.jpg


on the subject of the reliability of such a design:

"It's no secret the the M16 and AR-15 have suffered a reputation that includes lack of reliability. Since the first battles of Vietnam we have heard horror stories of our soldiers dying on the battlefield with their M16s torn down in what appeared to be an attempt to clear malfunctions under a hail of AK gunfire. Soldiers decried the smaller 5.56 round is inferior to the 30-06 round of their Garands.
While these flaws have long since been overcome - the reputations have stuck. Even today many preparers prefer the design of the AK-47 over the AR-15 due to it's incredible reliability - and it's hard to deny.

The same is true for the shorter barrel variant. When the M16s were first chopped down to 16 inch barrels, the gas system was insufficient to cycle the bolt - a problem that has been overcome by enlarging the gas port on the barrel. But the myths still perpetuate.
People on forums all over the internet will tell you how unreliable the "dissipator" design is without even understanding how it works today.
Many companies still offer a true rifle length gas system on a shorter barrel with great reliability. "
- FatalKitty


HOW TO build your own Dissipator: method 2
Everything you need to know in post #3 below

dieselpower 10-26-2011 9:38 PM

My HBAR is a 14.5” with perm Brake. I wanted a FF dissy. Please if you do not understand a step, do a quick Google search or YouTube video search. It will most likely answer all your questions. Videos give you a great deal of knowledge since you can see for yourself what is confusing you in print form.

This combination of parts does NOT allow the front flip up BUIS to lay flat in the down position. For that to happen the Quad-rail must be 1.5” shorter or the barrel needs to be 1.5” longer. If this is going to bug you… you need other parts.


Parts:
1) YHM Lightweight Rifle length Quad rail.
2) YHM HK Style Flip up front BUIS, 2piece clamp-on, no bayo lug.
3) YHM Specter 2 piece low-profile clamp-on Gas Block.
4) Barrel wrench
5) Upper block or other way of holding upper secure to torque nut.

Instructions:
1) Remove carbine hand guards.
2) Secure upper.
3) Remove gas tube.
4) Remove barrel from upper.
5) Remove Delta Ring, Slip ring and Weld spring. Place them away, you will not need them.
6) Secure barrel in vise.
7) Pound out the FSB pins
8) Since the Muzzle device can’t come off, cut the FSB off. Also cut the hand guard cap off as well. This is best done by cutting 50% or slightly more through the metal, and then use pliers to twist and break the remaining metal away. This keeps the cutting wheel far away from your barrel
9) Your barrel nut should now slip off the barrel. Place it away, you will not need it.
10) Install the YHM barrel nut / Hand guard nut with the locking ring. Refer to the instructions and YouTube for a video.
11) Install the barrel to the upper and have the lock ring all the way back.
12) Install the YHM Specter Gas Block. Make sure to leave a slight gap where a hand guard cap WOULD have been. This centers the gas block hole directly over the gas port on the barrel. Even if you butt the gas block up against the barrel step up, the holes will be close enough. YHM made the gas hole in the Specter Gas Block large enough to allow this. IIRC it’s only about 1.75mm anyway. Lock this down TIGHT. Don’t bother with Loc-tite the gas block will be heating past 500 degrees which will melt the Loc-tite. You can use a perma-tex sealant, The type used for engine head gaskets.
13) Screw the FF Hand Guards all the way in…ALL THE WAY as far as possible. This allows you to install the rear clamp of the FSB, since it will be under the rail when completed.
14) Clamp the YHM front Flip up sight directly against the Muzzle device. Keep it slightly loose.
15) With the upper in a vise, hang a red string in front of the muzzle. Stand behind the upper and look into and through the barrel. The string should run straight down the front post and straight through the barrel. This is detailed in the Military Armory manual TM9-1005-319-23, Chapt 3, and page 3-42. Look at my links for the manual. Align the FSB this way and lock the screws down
16) Align the Hand guard now by unscrewing it slightly and aligning the side screws. Then use the locking ring.

Here’s a crappy cell phone picture of my rifle. I will get a better shot of it this week end.
http://i655.photobucket.com/albums/u...y/YHMdissy.jpg

Ubermcoupe 10-26-2011 9:46 PM

:drool5:

FatalKitty 10-26-2011 9:56 PM

My "dissipator"
it's a rifle length gas system DMPS 16" barrel!

http://farm7.static.flickr.com/6171/...d3fafd70_b.jpg
the surefire MB556k at the business end!

GW 10-26-2011 10:18 PM

Very cool info
Thanks!:thumbsup:

Tangorox 10-26-2011 10:21 PM

This is what I'm waiting for!!!

FatalKitty 10-27-2011 8:33 AM

Cool write-up dieselpower! I've always wondered about building a free float dissipator, right on!

Tangorox 10-27-2011 11:26 AM

Does it have to be a rifle length gas system for a 16" barrel, which I am planning to purchase, or a midlength gas will do? I have a KAC RAS M5 on hand right now and planning to build a dissy around it. I am stuck with the delta ring & end cap to secure the KAC...no floaty for this build.

@Dieselpower...do you think it would look cheesy if I use the YHM flip up BUIS to secure the front end instead of the A2 FSB? Just getting some suggestions before going further with my plan.

@Thanks Fatalkitty for the topic.

Iggy 10-27-2011 11:38 AM

My past dizzy

http://iggycorp.com/gun/n4ffl1.JPG

FatalKitty 10-27-2011 11:39 AM

I've noticed a couple threads pop up and figured this was needed :) Thanks to diesel for the help and advice on this as well!

The gas block can be in carbine or midlenth position hidden under the handguards.

If you're stuck with a delta ring setup, you're kind of stuck with an A2 sight block as well - the YHM and MI flip ups don't have room to mount the A2 handguard cap for standard type guards to work.

I did see someone make a free floating MOE guard and I have been trying to find it and how they did it, that might be of interest to you as well. They were on calguns and the upper was for sale a few months back

FatalKitty 10-28-2011 6:42 AM

http://farm7.static.flickr.com/6111/...16db3c07_o.jpg

found this cool photo of the Colt 605a with attached mx148!

starsnuffer 10-28-2011 6:57 AM

Quote:

Originally Posted by Tangorox (Post 7396451)
Does it have to be a rifle length gas system for a 16" barrel, which I am planning to purchase, or a midlength gas will do? I have a KAC RAS M5 on hand right now and planning to build a dissy around it. I am stuck with the delta ring & end cap to secure the KAC...no floaty for this build.

@Dieselpower...do you think it would look cheesy if I use the YHM flip up BUIS to secure the front end instead of the A2 FSB? Just getting some suggestions before going further with my plan.

@Thanks Fatalkitty for the topic.

There are a lot of "mock dissipators" with mid length gas systems but a rifle length sight. They're not really dissipators, but anyone who doesn't know any better won't notice (nor care, but that's not the point). The "cool" factor that dissipators always had was the fact that they just didn't run right and required a lot of tweaking to get the timing to function properly. As mentioned in the threads above, all that noise has been solved, so you can just plug and play. Kinda does away with the cool factor of needing to know what you're doing to run one, but you should always buy the rifle that YOU want anyway.

With the advent of low profile gas blocks and rail mounted BUIS, and red dot optics, the need just isn't there for a shorter rifle with a maximized iron sight radius.

-W

FatalKitty 10-28-2011 9:31 AM

Quote:

Originally Posted by starsnuffer (Post 7401311)
...

With the advent of low profile gas blocks and rail mounted BUIS, and red dot optics, the need just isn't there for a shorter rifle with a maximized iron sight radius.

-W

for those that don't want to run optics because they like shooting with irons (which will be more precise than a 2 MOA dot) and those that want to use their existing barrel... the "slave" gas block is a great idea.
I would rather spend $50 on a new handguard and A2 sight post to convert to a "dissipator" than spend hundreds of dollars on free float rails or optics

starsnuffer 10-28-2011 10:27 AM

Quote:

Originally Posted by FatalKitty (Post 7402020)
for those that don't want to run optics because they like shooting with irons (which will be more precise than a 2 MOA dot) and those that want to use their existing barrel... the "slave" gas block is a great idea.
I would rather spend $50 on a new handguard and A2 sight post to convert to a "dissipator" than spend hundreds of dollars on free float rails or optics

That was kind of my point. A slave gas block isn't a dissipator. If your gas tube is connected to a low profile gas block mounted at mid or carbine length, then you still have a "middy" or a "carbine", despite adding a gas block/sight tower to the end of your barrel. There is nothing wrong with doing this! I'm not saying it's wrong, just saying it's not a dissipator. In my thread above, I did mention that you could do the same thing running a longer rail and mounting a rail mounted iron sight. Often this weighs less then a slave gas block.

-W

loosewreck 10-28-2011 11:27 AM

Here's some quick and dirty before and after shots of my Shrubmaster Dissipator upper.

Its a bit heavier than my M4 upper, but the Sully Stock with Carry handle and, currently, the UBR balance it out nicely.

So far its been running reliably with a BCM BCG and standard carbine buffer and spring.

I picked up the upper during the Obama scare from another Calgunner who said he only ran .22s threw it.


Semi Kissed-Out Before
http://i440.photobucket.com/albums/q...23/StagRef.jpg


Magpul Fanboyed After
http://i440.photobucket.com/albums/q...23/Dissy25.jpg

jkast003 10-28-2011 12:24 PM

I put this together with input from my son. This is what he uses on our range trips. Del-ton upper and lower, various Magpul items and a PA red dot.

http://i569.photobucket.com/albums/s...3/IMG_1788.jpg

Iggy 10-28-2011 12:27 PM

Quote:

Originally Posted by FatalKitty (Post 7396520)
I did see someone make a free floating MOE guard and I have been trying to find it and how they did it, that might be of interest to you as well. They were on calguns and the upper was for sale a few months back

That would be me. Whitemamba owns it now.

Quote:

Originally Posted by Iggy (Post 6103180)
After waiting 8 weeks from White Oak, I got my dissipator upper. Having owned a Noveske and selling to fund my bolt action addiction I wanted to go back to something basic and use iron sights. I also wanted to keep the rifle at 16", but liked the idea of having the long sight radius of the 20" service rifle.

I came across dissipators and what a perfect pair. I couldn't get a Noveske in dissipator format so I searched around to find the right twist, but nothing came up so I gave WOA a call.

Bingo! It exactly what I wanted. They custom built the upper for me and it turned out great. The best part, and what makes this dissipator unique, is that the handguards are free floated. Since WOA makes an awesome barrel I didn't want to lose accuracy by having handguard to barrel contact.

The sad part is I have to wait a few months for the lower to arrive. The good news is it will be a Noveske FFL lower!

Pics:
http://iggycorp.com/gun/woad1.JPG

I got the AAC Blackout brake incase I decide to go featureless
http://iggycorp.com/gun/woad2.JPG

Chrome BCG
http://iggycorp.com/gun/woad3.JPG

Freefloat Tube
http://iggycorp.com/gun/woad4.JPG

No contact with front sight
http://iggycorp.com/gun/woad5.JPG


FatalKitty 10-28-2011 1:27 PM

Quote:

Originally Posted by jkast003 (Post 7402970)
I put this together with input from my son. This is what he uses on our range trips. Del-ton upper and lower, various Magpul items and a PA red dot.

[IMG]http://i569.photobucket.com/albums/ss138/jkast003/IMG_1788.jpg[IMG]

YES! That is a good looking dissipator right there!
At first I didn't like the look of the MOE guards on it, but the more I see them now I love it that way, just seams to fit right


Quote:

Originally Posted by Iggy (Post 7402982)
That would be me. Whitemamba owns it now.

That's the one! Thanks for posting that Iggy, I thought I had it in my PMs still

Inquirer 10-28-2011 1:47 PM

Terrific thread, FatalKitty. Good to have a go-to resource for all Dissipator inquiries. Would be nice if more be-all and end-all info threads like this would pop up.

--Inq

FatalKitty 10-28-2011 7:31 PM

Quote:

Originally Posted by Inquirer (Post 7403371)
Terrific thread, FatalKitty. Good to have a go-to resource for all Dissipator inquiries. Would be nice if more be-all and end-all info threads like this would pop up.

--Inq

took me a few hours to get it done, so I appreciate the notice :cool2:
it's something that I figured needed to be done, and I can't wait to see more photos of people's builds!

FatalKitty 10-31-2011 6:18 PM

http://farm7.static.flickr.com/6212/...972082df_b.jpg


updated photo of the dissipator - fired here by the lovely Hannah Ray! (http://www.facebook.com/hannahraymodel)

Clutch-n-Throttle 10-31-2011 6:35 PM

Quote:

Originally Posted by jkast003 (Post 7402970)
I put this together with input from my son. This is what he uses on our range trips. Del-ton upper and lower, various Magpul items and a PA red dot.

http://i569.photobucket.com/albums/s...3/IMG_1788.jpg

That looks like my gun. Great minds think alike. :)

DasBoost 10-31-2011 7:09 PM

This is a great resource!! I've consulted this thread a lot. My AR build will probably be a featureless dissipator build, either CMMG or Bushmaster. :thumbsup: Great thread.

loosewreck 10-31-2011 7:18 PM

Don't forget Palmentto State Armory also sell Dissy uppers with 1/7 Chrome Lined 4140 Carbine gas and 4150 mid-length gas barrels.

FatalKitty 10-31-2011 7:20 PM

Thanks loose! I plan to edit the OP and "how to" posts with more details on where to get stuff as well.
Any additional sources you guys have will be super helpful!

apbrian112 10-31-2011 11:20 PM

Quote:

Originally Posted by FatalKitty (Post 7394019)
http://farm7.static.flickr.com/6163/...56ea3bcd_b.jpg

My "dissipator"
it's a rifle length gas system DMPS 16" barrel!
Magpul sexyness all over it and a Primary Arms gen6 Micro

Diggin this set up! May have to build one like this...

darqhelmet 11-01-2011 9:58 AM

This thread gave me a great idea for my .22lr AR. :)

Tangorox 11-01-2011 10:20 AM

Quote:

Originally Posted by FatalKitty (Post 7420121)
http://farm7.static.flickr.com/6212/...972082df_b.jpg


updated photo of the dissipator - fired here by the lovely Hannah Ray! (http://www.facebook.com/hannahraymodel)

Hey FatalKitty
Nice pix with the hottie!
Is your rifle a 16" barrel, midlength or rifle length gas system?

chicoredneck 11-01-2011 10:23 AM

cool thread and very informative

FatalKitty 11-01-2011 2:49 PM

Tangorox, my rifle uses the rifle gas system
Shot wolf all day long yestersay, stuff is crap... i could noticably feel the lesser recoil from it compared to the usual lake city stuff i shoot and it wouldnt lock back on the last round. Also had about 5 fte with it out of about 500 rounds of it.
The 500 rounds of lake city i shot functioned flawlessly.

I have a video of me shooting but not sure if i should post it... not wearing eye pro and im just shooting for the camera

Capita159 11-01-2011 3:42 PM

this thread is making me miss my old Dissi witha A1 stock.....

http://farm4.static.flickr.com/3455/...e490ddf8e8.jpg

trg-s338 11-01-2011 4:09 PM

I've got a 20" rifle length port and barrel I'm going to have cut to 16". The question is, what is the size of the port on reliable rifle length dissipators? Is there enough dwell time to cycle the rifle reliably? Not that its of any consequence for CA rifles, but I am curious how a rifle length ported barrel at 16" would function in full auto? Would it be reliable as well?

FatalKitty 11-01-2011 4:38 PM

Quote:

Originally Posted by trg-s338 (Post 7425156)
I've got a 20" rifle length port and barrel I'm going to have cut to 16". The question is, what is the size of the port on reliable rifle length dissipators? Is there enough dwell time to cycle the rifle reliably? Not that its of any consequence for CA rifles, but I am curious how a rifle length ported barrel at 16" would function in full auto? Would it be reliable as well?

I put an email into DPMS to see if they will tell me what the size port is. if they don't I will have to resort to taking the post off an measuring it myself.


the DPMS barrel I have cycles just fine under rapid fire

trg-s338 11-03-2011 6:05 PM

I will continue to search for that port size also, Fatalkitty. If you happen to measure yours, that's a piece of info we all could use in a reliable rifle length build. Thanks.

dieselpower 11-03-2011 6:35 PM

Quote:

Originally Posted by FatalKitty (Post 7425319)
I put an email into DPMS to see if they will tell me what the size port is. if they don't I will have to resort to taking the post off an measuring it myself.


the DPMS barrel I have cycles just fine under rapid fire

Quote:

Originally Posted by trg-s338 (Post 7436864)
I will continue to search for that port size also, Fatalkitty. If you happen to measure yours, that's a piece of info we all could use in a reliable rifle length build. Thanks.

the port sizes was listed in the AR15.com dissipator thread. Its like 40 pages... I am sorry if you go through all 40 pages and its not there. :facepalm: I know two guys where talking about it in a dissy thread...I just can't remember where. I think it was ar15.com. May have been in a Industry forum over there as well.

aznanimekid 11-14-2011 12:07 PM

looking into building a dissy and had a few questions.

right now im debating between rifle or midlength. the one issue i have with rifle length is whether or not i will run into problems with over/under gassing with certain ammo. i know fatalkitty has already posted he had issues with wolf and i'm a little iffy if any other ammo might turn up the same.

also which buffer combo should one run with a dissy? is it different if i change the gas system from rifle to mid to carb?

FatalKitty 11-14-2011 3:33 PM

You won't have to worry about overgassed with a dissy... if anything you would run into something that is undergassed. But really, there aren't many ARs out there that will reliably cycle wolf ammo - in fact my dissy does it better than my carbine. it runs all other steel ammo just fine... but wolf is crap and my guns hate it.

The buffer is dependant on your stock, not the gas system. a "rifle buffer" is for the A2 stock that is a fixed rifle stock... the "carbine buffer" is for a carbine stock like a collapsible stock

the cool thing about about using a mock dissy is that you can have free float handguards and a lighter setup (can only find HBAR or mid dissy barrels right now)
and it seams to be the way everyone does it.

I went with the rifle gas systems for a couple of reasons:
1. not many had that set up and I wanted it
2. heavy barrel keeps the muzzle climb down
3. smoother operating gas system - as this gun was going to be iron sights almost exclusively I wanted to keep muzzle jump and recoil down as much as possible
4. I wanted to build it myself, something I wasn't able to do for my first AR with a dual gas block setup (this requires modifying the barrel so that the A2 front post can be pinned in place

till44 11-14-2011 4:51 PM

Great thread. I've been planning on a "featureless" dissipator build for awhile, great motivation to get all the needed parts and finish it.

RugerNo1 11-14-2011 5:06 PM

This thread is making me want one of the JSE DPMS or PSA dissipators for a play-around/go-fast featureless rifle...


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