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Old 01-24-2017, 10:46   #1
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Building Myself a Dissy...

After resisting the AR bandwagon for more than a decade, I have finally decided to climb aboard. It all started with a DPMS LR-308T. Modifying that rifle to suit my needs (and wants...) has made me decide to build a 5.56 AR.

So far, I have purchased a Del-Ton Dissipator Barrel "kit" (FSB, Triangular HG cap, & barrel nut). This is a "true Dissipator," i.e., rifle-length gas system, not a carbine- or mid-length setup with a low-profile gas block.

My vision for this rifle includes an A2 buttstock, A2 handguard, and a "National Match" free-float tube. I will be mounting a Harris #5 bipod adapter (in A2 handguard) for sling use and occasional bipod use. Looking to build a "sleeper" rifle, I guess.

Common sense tells me that a short, heavy barrel will be stiffer than something longer and/or lighter. But that same common sense tells me a bipod and/or slinging up tight will affect POI if the barrel is not free-floated.

My question for y'all is this: on a 16" HBAR, how much of a difference is a free-float kit going to make, as far as accuracy is concerned? Anyone have any before-and-after groups showing the difference between "traditional" handguard mounting and free-floating? Even groups shot with an aftermarket FF tube/rail/whatever would give me some idea.
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Old 01-24-2017, 14:31   #2
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I'm not sure if you've had your hands on a HBAR profile barrel or not, but those suckers are pretty beefy between the gas block and the barrel extension. I think you'd really have to lean into that thing pretty hard (hard enough I'd be worried about breaking something else) to get a noticeable POI shift to occur. Others may disagree, but I wouldn't be inclined to worry about it unless I was building something with a lightweight or pencil profile barrel.
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Old 01-24-2017, 17:00   #3
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Spare no expense on the barrel and the trigger. Perfection starts here.
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Old 01-24-2017, 21:09   #4
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Originally Posted by cjclemens View Post
I'm not sure if you've had your hands on a HBAR profile barrel or not, but those suckers are pretty beefy between the gas block and the barrel extension. I think you'd really have to lean into that thing pretty hard (hard enough I'd be worried about breaking something else) to get a noticeable POI shift to occur. Others may disagree, but I wouldn't be inclined to worry about it unless I was building something with a lightweight or pencil profile barrel.
Yeah, this one is .875" from barrel extension to FSB. .750" from there to the the muzzle threads.

Originally Posted by chill1955 View Post
Spare no expense on the barrel and the trigger. Perfection starts here.
Since I already have the barrel, is that a recommendation to float it?

Last edited by COBrien; 01-24-2017 at 21:32.
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Old 01-25-2017, 07:38   #5
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In theory, a free-floated barrel should always be more accurate than an identical barrel that has a standard handguard on it. Free floating it allows the barrel to vibrate or resonate (whatever you want to call it) as it pleases. That standard handguard can interfere with those harmonics. Barrel flex is kind of a different ball of wax. As I said before, the HBAR profile barrel is going to be relatively immune to that sort of thing. Despite all that, AR's can still be quite accurate with standard handguards on them. As a matter of fact, my current coyote hunting AR (pending upgrade) is equipped with a standard handguard and A2 front sight. On coyote sized targets, I'm pretty confident with it out to 250 yards. I'm sure a better shooter could stretch it out even farther.

In the end, it boils down to personal preference. If your goal is to build the most accurate rifle you can build for use in DCM or other service rifle matches, I'd say go with the free float tube. If the rifle is just for target shooting at the range, you'll probably be just as happy with the standard handguard.

What I believe chill was getting at is that the 2 biggest factor's that determine a rifle's accuracy are the barrel and the trigger. You already have your barrel - my current coyote rifle happens to be a Del-Ton, too. There are probably some better brands on the market, but I believe Del-Ton barrels are good quality for the price. The other thing to consider is that there aren't very many manufacturers making dissy barrels. Getting one somewhere else likely would have been a custom order and probably a lot more expensive.

That leaves the trigger. The stock milspec triggers tend to be farily heavy, with a lot of creep. There are a lot of aftermarket triggers you can go with. Timneys are expensive, but super easy to install and snap like a glass rod. I'm a big fan of the JP Enterprises adjustable fire control group. They're a component trigger, kinda like the stock milspec trigger, but there are a couple set screws you have to adjust to optimize performance. If you get them dialed in just right, they're darn near as good as a Timney for half the price. Again, there are a lot of other good brands out there, but those are just a couple that I have experience with. I do think that installing a good trigger will go a long way toward making your dissy the "sleeper" you want it to be.
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Old 01-25-2017, 08:21   #6
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cjclemens: My thinking on free floating the barrel is in line with what you posted.

Is it better? Yes, without question.

Will I notice it? Probably not.

Will the rifle end up being more accurate than I am on any given day, regardless of handguard setup? Probably so.

After sleeping on it last night, I've decided to build the rifle "as-is," since the barrel arrived with the FSB, HG cap, and barrel nut all in place. I just need to install a delta ring, weld spring, and snap ring, and it's ready to go on my upper (that I haven't ordered yet -- I've limited myself to spending $150ish per month on this build...).

In the event I'm not happy with the accuracy I get from the standard HG configuration, I'll give the DCM FF sleeve a shot. I'll be swapping my FSB anyway at that point (to a Fulton Armory "Power Wedge" FSB, rather than a pin-on), so it won't be that big a deal.

Or maybe I'll go with JP's adjustable FSB. I'm planning on purchasing a Sig SRD762QD as a "do-all" rifle suppressor and would prefer an adjustable gas block. Though, as under-gassed as Dissipators tend to be, that may not even be an issue.

As far as triggers, I've read great things about the LaRue MBT-2S, and will look into the JP setup.

While I love the RRA 2-Stage that's in my .308 AR, I learned after purchase that they go "mushy" after awhile. I don't consider FCGs to be sacrificial parts, so I'll be avoiding RRA triggers from now on...
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Old 01-25-2017, 19:33   #7
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Sounds like you have a pretty good plan already. I think youll be pretty happy with the standard HG configuration.

However, I would definitely think about the adjustable gas block, if you do plan to run it with a can. Because dissy's tend to be undergassed from the lack of dwell, the gas port size is usually cut pretty generously. Putting a can on could take you from "just enough" to "way overgassed" pretty quickly. I have used a couple of the JP adjustable gas blocks. They are nice, but they are a "set it and forget it" kind of system. If you plan to always run it with a can, it would work well. If can use is going to be intermittent, one of those setups that has a dial and markings on it might be better, so you can find your desired settings and not have to re-tune. Cans are a bit outside my wheelhouse, so those are just my random thoughts on the matter. You should definitely do more research.

Good to know about the RRA trigger. I had considered using one until I found the JP setup. I know a few guys who swear by those RRA triggers, but theyre mostly coyote hunters and definitely don't do any high volume shooting.
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Old 01-26-2017, 07:22   #8
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That is a good point, which I hadn't thought of.

With an open muzzle, the rifle needs a larger port (in this case, .098") to bleed off a sufficient volume of gas to cycle the BCG. Once you obstruct the flow of gas from the muzzle with a suppressor, the larger port will allow significantly more gas to flow through the tube than a smaller port on a "normal" rifle would.

It seems JP is the only company producing an adjustable FSB. I love the design of the SLR Sentry series (and am considering a 7 Series for my .308 AR), with their serviceable detent setup, but I'd like to keep the FSB. It is possible to modify a FSB to make it adjustable, but I do not have the tools any more (shop was burglarized and didn't have quite enough insurance...) to feel comfortable DIY-ing that particular project.

I have discovered, though, that MGI makes a "regulated" (adjustable) gas tube. What a trick little part that is:



The adjustment screw is designed to sit directly below one of the holes in an A2 handguard. Talk about a sleeper...
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Old 01-26-2017, 12:51   #9
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check out this new barrel that I just got to demo. its from BSFbarrels I love it
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Old 01-26-2017, 15:49   #10
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I don't mean to say the JP wouldn't work. IIRC, you put some blue thread locker on the set screw that throttles the gas. Once you back it out far enough that the bolt cycles 100% reliably, you put some blue thread locker on another set screw that jams up against the adjustment screw. You'd just have to set it with the can then set it without the can and remember how many times to turn the screw when you switch back and forth. That, and remember to keep the allen wrench in your range bag.

Who knows - maybe a suppressor won't even put that much extra back pressure on it. If you check around some other forums, I'm almost certain you'll be able to find someone who has put a can on a dissy. They'd be able to solve this mystery better than I can.
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Old 01-26-2017, 18:37   #11
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Originally Posted by rodneyw View Post
check out this new barrel that I just got to demo. its from BSFbarrels I love it
Are they building lightweight Dissipator barrels?

Originally Posted by cjclemens View Post
I don't mean to say the JP wouldn't work. IIRC, you put some blue thread locker on the set screw that throttles the gas. Once you back it out far enough that the bolt cycles 100% reliably, you put some blue thread locker on another set screw that jams up against the adjustment screw. You'd just have to set it with the can then set it without the can and remember how many times to turn the screw when you switch back and forth. That, and remember to keep the allen wrench in your range bag.

Who knows - maybe a suppressor won't even put that much extra back pressure on it. If you check around some other forums, I'm almost certain you'll be able to find someone who has put a can on a dissy. They'd be able to solve this mystery better than I can.
Oh, I'm sure the JP would work fine. It's the $150 price tag I'm not a big fan of. Plus I do like the idea of doing something different with OEM-style parts -- something not everyone is doing.
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Old 01-27-2017, 10:25   #12
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Originally Posted by COBrien View Post
Are they building lightweight Dissipator barrels?



Oh, I'm sure the JP would work fine. It's the $150 price tag I'm not a big fan of. Plus I do like the idea of doing something different with OEM-style parts -- something not everyone is doing.
Good luck with your build. I'll be waiting for the range report thread.
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Old 01-27-2017, 11:41   #13
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Originally Posted by cjclemens View Post
Good luck with your build. I'll be waiting for the range report thread.
Thank you, sir!

I plan on posting pics and updates in this thread throughout the process. It's going to be a months-long build, at least April or May before I have the upper ready to go.

I'll try running it on my wife's Bushmaster Carbon-15 carbine lower at first, then start building my own lower (she loves collapsible stocks, and I'm more into fixed stocks with rifle-length tubes...).

Based on other comments online, I'm not optimistic it will run well with a carbine buffer/spring setup, but I may be pleasantly surprised.
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Old 01-31-2017, 14:04   #14
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As already mentioned Dissi's have a short dwell time between the muzzle and gas port, so these rifles may only function with better quality higher velocity rounds Because of the longer time to the gas port from the chamber, I doubt over gassing will be a problem. I have had one. I would not worry about overgassing, in a long action it is not usually a problem like it is in a short system due to pressure drop in the chamber. In other words, I would not bother with an adjustable gas block unless you actually had problems, and I don't think you will. I think you will be undergassed anyway. that was my experience.
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Old 01-31-2017, 14:53   #15
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Originally Posted by D2wing View Post
As already mentioned Dissi's have a short dwell time between the muzzle and gas port, so these rifles may only function with better quality higher velocity rounds Because of the longer time to the gas port from the chamber, I doubt over gassing will be a problem. I have had one. I would not worry about overgassing, in a long action it is not usually a problem like it is in a short system due to pressure drop in the chamber. In other words, I would not bother with an adjustable gas block unless you actually had problems, and I don't think you will. I think you will be undergassed anyway. that was my experience.
Definitely appreciate the input. This is what I've heard (and it makes sense) when talking about running with a "naked" muzzle.

I'm wondering if/how running a suppressor will affect the reliability of the rifle without an adjustable block or tube.

I guess it's really not difficult to swap out a gas tube down the road should I decide I need an adjustable tube...
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Old 02-01-2017, 13:07   #16
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Second batch of parts is on the way...

M4 Upper
Upper Parts Kit
Delta Ring, Weld Spring, and Snap Ring
NMA2 (.040") Front Sight Post, Detent, and Spring
Rifle-Length Gas Tube and Pin

all from Fulton Armory. They've got a 10% store-wide sale going on right now. That brings all the parts down to about the price of no-name parts on eBay. I just have a problem paying $15 for USPS shipping...

I'll get the upper together, then order the BCG (NiB? Chrome?), A2 Handguard, and probably my lower during the Presidents' Day Sale (15% off).
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Old 02-02-2017, 05:27   #17
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I'd just get a premium BCG from Palmetto State Armory. They're made by Toolcraft (a top-shelf OEM supplier), and 100% good to go. Palmetto has them on sale under $100 right now, which is a heck of a deal.
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Old 02-06-2017, 13:09   #18
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My upper and other associated parts came in the mail today. That box was deceptively large -- $150 worth of upper parts sure doesn't look like $150.

Now, for some bad news (for me anyhow...).

I told the wife the only thing I wanted for my birthday was her permission to build a rifle. Her response was (correctly, I might add...) that I have too many projects going on right now and to take care of those first, before jumping headlong into an AR build.

This is one of those times during a marriage when -- for several reasons -- permission is very much preferable to forgiveness. So, in the spirit of trying to get permission ahead of time, this project is being placed on hold.

That is, right after I pick up that green ArmaLite A2 furniture set that's on clearance...
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Old 02-07-2017, 06:00   #19
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Originally Posted by COBrien View Post
My upper and other associated parts came in the mail today. That box was deceptively large -- $150 worth of upper parts sure doesn't look like $150.

Now, for some bad news (for me anyhow...).

I told the wife the only thing I wanted for my birthday was her permission to build a rifle. Her response was (correctly, I might add...) that I have too many projects going on right now and to take care of those first, before jumping headlong into an AR build.

This is one of those times during a marriage when -- for several reasons -- permission is very much preferable to forgiveness. So, in the spirit of trying to get permission ahead of time, this project is being placed on hold.

That is, right after I pick up that green ArmaLite A2 furniture set that's on clearance...
I wouldn't worry about that too much. As you mentioned, all of us married guys have been there a time or two, at the least. Those parts certainly won't spoil, while you work on getting your schedule cleared up. If it makes you feel any better, I'm temporarily on an AR-build hiatus that's budget related. I built my 300BLK last summer (my birthday present to myself) and a lightweight carbine for the wife. As such, I'm limited to picking up a few small parts here and there. Its a major bummer, but that's just how life goes. All those other financial obligations that come with adulthood have to be taken care of before you buy any toys.
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Old 02-14-2017, 07:01   #20
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So... This whole "waiting for permission" thing is difficult for me...

My ArmaLite green furniture set came in yesterday. Gorgeous, and will give the rifle a real "old school" look.

I also got an e-mail from PSA this past weekend. One of their "weekend deals" was a NiB BCG and "Premium" 7075 Charging Handle for $119.99. Identical parts from Fulton Armory would have cost me anywhere from $160-190, depending on the sale going on. I'd decided to forego the NiB BCG due to cost, and the "GI" BCG and CH would have cost me $135-160.

The PSA BCG and CH are on their way.

That purchase completes the parts I need to put my upper together. Total investment is around $550, including shipping, taxes, and the buttstock and pistol grip (purchased as a package from ArmaLite). Parts-only cost is right at $500.

The worst part (best part?) is that the lower will take significantly less funds to get together. Like a grand total of between $300-400, including a NM trigger.

This rifle has been an idea in my head for a while now, and it just so happens someone at ARFCOM built one almost identical:

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Old 02-14-2017, 07:23   #21
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The dissy in that pic looks pretty sharp. What rear sight are you gonna go with?
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Old 02-14-2017, 07:26   #22
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I wavered back and forth for a while about the rear sight. A friend of mine has a stash of Matech rear sights, but I ended up getting a KAC Micro 600 on eBay pretty cheap.
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Old 02-15-2017, 07:54   #23
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That's what I call a minimalist iron sight, for sure. I bet it weighs next to nothing. I'm considering a 20" iron sight rifle build, and I cant decide between just doing a no-frills A2 carry handle upper or using a flat top with a fixed rear iron. I like the looks of the Daniel Defense A1.5 rear sight. It definitely looks like a sturdy platform.
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Old 02-17-2017, 08:20   #24
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Originally Posted by cjclemens View Post
That's what I call a minimalist iron sight, for sure. I bet it weighs next to nothing. I'm considering a 20" iron sight rifle build, and I cant decide between just doing a no-frills A2 carry handle upper or using a flat top with a fixed rear iron. I like the looks of the Daniel Defense A1.5 rear sight. It definitely looks like a sturdy platform.
According to KAC's website, it weighs 1.5 oz. This isn't going to be a "lightweight" rifle by any measurement, but at least it won't be weighed down by the rear sight.
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Old 02-23-2017, 06:48   #25
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Last Saturday I had to run to the office (which is where I'm hiding these parts...) to make a couple of phone calls.

While I was there, I mocked up the upper:



At the time, my Sig SRD Micro Brake, BCG, and CH hadn't come in yet (I told you guys this "waiting for permission" thing wasn't working...), and I haven't had a chance to mock everything up since I got them in...
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