Which 16" AR upper style?

Dissipator gives you a longer sight plane for iron work. The longer gas system are supposed to be softer shooting as well.

I went w/ the mid-length when I bought my first AR -- so far so good -- no complaints

Sort of depends on what you intend to do with it. Anything will suffice to punch holes in paper or pop cans. Both will shoot accurately--quality of trigger pull is far more important than barrel length and worth investing in. Biggest differences are relative handiness and down-range lethality with a specific round. With the old (and more lethal) 55 gr FMJBT M193 round, the 16" weapon is good for about 150 yards max; the longer 20" barrel extends that to 200 yards. Use of the 62 grain M855 round degrades even those numbers.

If shooting organized high power then the match type 20" A2 type rifles rule. If not...

I opted for the basic 16" M4gery configuration and stuck a compact ACOG on it. IMHO less is more and simpler is better. .

IMO, there's no advantage to the M4/CAR over a Midlength except that the M4 looks more like what the military uses(but they have a 14.5" barrel).

The Midlength has a longer sight radius, it's easier on your bolt and will have slightly better extraction performance due to a softer gas impulse. A govt. profile Midlength is lighter than an M4 profile (HBARs both weight the same). If you are the type who likes rails, the Midlength give you more room on the rail. Plus the Midlength doesn't look like Pinoccio.

DMK is right. The mid-length is easier on the bolt and extractor. Less gas blast. If you shoot a 20" a lot and a 16" you can see and feel the difference. Mid-length deals with it better than the CAR/M4 length system.


What is the purpose of this AR?

i am a definite fan of the 16" rifle-length setups. i particularly find the long sight-radius to be easier to use, and i like the improved pointability. full-length handguards are nice too.

I like the long sight radius of the Dissipators too, plus they look cool. However, almost all use a CAR/M4 gas system. So actually you're only gaining the sight radius and some barrel weight.

CMMG makes 'em with Midlength gas systems though.

I always thought that the "system" was whatever the handguard setup was--and that, by default, if you bought a dissipator, you got a rifle system

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Not necessarily. You need to pay attention to what's under the handguards. For example, this Bushmaster barrel has it's gas block at the same position as a CAR/M4. The front sight block just holds the sight post and handguards on. (also note that this particular barrel is a Heavy Barrel profile. Bushie also makes this barrel in a lighter M4 profile) Caveat Emptor

Boy, that's a rip.

Ash

What are the differences between CAR/M4 system, Midlength system, and Rifle system

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Aside from sight radius and handguard length, the gas systems bleed off the gasses at different points, with the CAR/M4 system being closer to the chamber, the Rifle system being furthest and the Midlength being about right between them.

It's really a timing issue:

The Rifle system is the most reliable because the pressure has subsided a bit by the time the bullet passes the gas port. This means the gas tube pressure is lower, and the force on the bolt/carrier is lower. The lower pressure in the chamber has also allowed the brass to 'relax' a bit so it's easier to extract it. It won't work with a 16" barrel though because the bullet would leave the barrel too soon after passing the gas port and port pressure would drop to nil before the system cycled.

With the CAR/M4 system, the gas port is closer to the chamber, gas pressures in the barrel are much higher at that point and the bolt gets slammed back harder (don't forget gas pressure is injected between the bolt and carrier, forcing them apart slightly before the carrier is slammed back). Due to the timing of the closer gas port, the pressures are still high in the chamber, so the brass is still expanded out against the chamber walls making extraction more difficult. The CAR/M4 system is the reason for the stiffer extraction springs and rubber 'O' rings on the market to keep that extractor tight on the case rim.

The Midlength, while operating with higher gas tube pressures than a rifle length, has slightly later timing and a softer gas impulse than the CAR. For a 16" barrel there is no good reason to go with the CAR/M4 gas system other than for cosmetic reasons.

CMMG (www.cmmginc.com) makes 16" Dissy type barrels with a midlength gas system.



They also make a 18" that uses rifle length handguards also and it too has a midlength gas system.

I decided to go with a 18" barrel with either mid or rifle length gas tube and handguards. I figure splitting the difference between 20" an 16" was as good an idea as any. Besides, the 18" barrel gives up very little to a 20" tube ballistically and very little in handiness compared to a 16" gun. CMMG has about the most options you're gonna find on the market aside from a custom build.

I decided to go with a 18" barrel with either mid or rifle length gas tube and handguards. I figure splitting the difference between 20" an 16" was as good an idea as any. Besides, the 18" barrel gives up very little to a 20" tube ballistically and very little in handiness compared to a 16" gun. CMMG has about the most options you're gonna find on the market aside from a custom build.

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Most the shooting I tried with an Ar15 had this setup. I much perferred the sight placing the action of the rifle with the longer gas tube. There was something about the 16 inch barrel that wasn't so comfortable. Though I do perfer the Ar15a2 setup to the shorter M4 wannabes.

Generally speaking, dissipators are cosmetic (CMMG being the notable exception). They use a CAR length system under the handguards, not a rifle length. Just the sight radius and handguards are rifle length. A rifle-length gas system on a 16" barrel is a no-no.

And while the M4/CAR system results in slightly more abuse to the gun, there are literally tens of thousands (if not hundreds of thousands) of these carbines out there. They are not beating themselves apart.

BTW, I'm leaning towards a Dissipator-style rifle for my AR-15 too. To my knowledge, here's who makes them: Bushmaster, CMMG, Model 1 Sales, DPMS. I'm probably going to go with the DPMS since they're so inexpensive from Midway if you have a C&R, but it only comes as an A2 (fixed carry handle). Otherwise, I'd get the CMMG since it can be had as a flattop with a mid-length system. Still haven't decided yet though.

I like the long sight radius of the Dissipators too, plus they look cool. However, almost all use a CAR/M4 gas system. So actually you're only gaining the sight radius and some barrel weight.

CMMG makes 'em with Midlength gas systems though.

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They made my midlength dissipator upper. I just wish their medium contour bbl (the only profile they're offered in) was a little lighter.

A rifle-length gas system on a 16" barrel is a no-no.

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DPMS make such a rifle, the `A2 Tactical 16"'.

This A2 Tactical 16?

Nevermind, DPMS appears to have the pics screwed up. The Build it Now link shows this barrel on it:

yeha, i noticed the thumbnail was wrong. if you click on it though, it'll show you this.

Im currently building a Dissy inspired system. Im basing it on an 16" alexander arms 6.5mm grendel upper which comes with a mid length system. Im pulling off the gas block and replacing it with a low profile one and bolting up a Rifle length floating 4 rail Handguard. Itll leave about 3 inches of barrel poking out the front.

Panther™ A2 Tactical 16"

DPMS A2 Tactical 16"

If you want a dissy, go CMMG.

OK, to kind of go along with the CAR vs Middy vs Dissy (LOL) vs Rifle...

What about the rifle length gas tubes that curl around the barrel and are made to be used on the carbine systems? Do they help, work, any good? Advantages/disadvantages?