AR-15, 17" barrel, rifle-length gas: any downsides?

[MatthewVanitas]

(WARNING: this contains very geeky discussions of different gas-systems for the AR-15. You're probably far happier not reading this, and just enjoying what you already have. I was happier when I was ignorant)

Now I'm more confused more than ever.

First, I had a CAR-gas Dissipator. Works just great, swallows 55gr Wolf like candy (yes, it'll wear my extractor a little faster). Has a little kick to it, relative to other .223 rifles.

Then I start reading about how midlength-gas will give less felt recoil, and less wear and tear. So I was thinking of getting a nice CMMG middy.

Now I'm hearing more and more about 17" and 18" uppers with rifle-length gas. Does adding 1" to my barrel and moving to rifle length offer notable advantages over midlength? Will it bounce about notably less than the 16" CAR-gas?

If a 17" with rifle-gas works great, then it should have all the advantages of a rifle-length (sight radius, gas system, rifle-length handguard systems), and only lose whatever velocity you lose with those 3". Does a 17" rifle swing just about the same as a 16" Dissipator?

I have a 20" SP1 (slabside) upper, and will be trying that out side by side with my 16" CAR-Dissipator to check the difference in handling/recoil.

Again, I'd probably be just as happy if I didn't know anything about all this. I do note that the Dissy bounces more than the M16A2 I was issued, but that's about it.

I am a bit confused as to why so many mfgs offer 16" CAR-gas rifles instead of midlength or 17" rifle-gas. Is it just pure market inertia? Anyone predict that 16" CAR-gas will be in the minority in five years?

-MV

 

[BozemanMT]

I have 2 with 17" rifle length gas systems, built at the suggestion of Zak Smith (who's forgotten more than I know) and DAMN
They are the thing.
You don't notice the extra inch, and it's short and movable, but no beating on you like a shorter gas sytem and insanely reliable.
Light, etc
You just need a custom barrel to do it.
talk to Paul at MSTN (www.mstn.biz) and he'll put you something amazing together.
I wouldn't go 20" again, The longest I would go is 18" (which works too), it's just so much easier to move.

 

[Zak Smith]

17/rifle works well and balances great.

[ link to LARGER image ]

 

[BozemanMT]

Mine look just like that.
They are amazing shooting, I really can't recommend them highly enough.
Except mine are ARFCOM approved EBR black
I must admit the camo is pretty cool there Zak.
What's with the OJ bloody glove in the picture?

 

[Zak Smith]

Defective orange paint nozzle.

 

[MatthewVanitas]

If I have a 20" SP1 upper, can I get a 'smith to trim it down to 17", or are there more complicated tweakings that need to be done with the gas system?

I know that Mongo on ARF used to cut M16 uppers back to the FSP and open up the gas system, but that's more of a "Dissipator w/ Rifle-gas" than just a short rifle.

My impression is that SP1 uppers aren't particularly valuable unless part of a complete rifle, so don't think it would be blasphemy to chop this one.

-MV

 

[dm1333]

Is anyone making an upper with a 17 or 18 inch barrel? I just found out yesterday that my transfer to Michigan (and out of CA!!!!!!!!!!) will be in 4 or 5 months, once I get settled in there it will be time to get an AR. I like the collapsible buttstocks but want a longer barrel. Is it possible to just cut the 20 bbl down 2 or 3 inches? I've been lurking over on one of the AR forums but this thread caught my eye.

edit: I should have asked if there is anyone else besides CMMG making an upper with a 17 or 18 inch barrel. Does CMMG have a good reputation for quality? I have seen others recommending them, does anyone out there have any problems with them?

 

[Zak Smith]

All the custom guys can do 17-18". I recommend MSTN if you can afford it, but there are a bunch of others.

 

[BozemanMT]

What Zak said.
CMMG does fine work too
MSTN rocks, call Wes or Paul and put them to work.

You can also get a from the factory LMT MRP upper with a 18" SS barrel. (of course, that's about the same or more than a custom build, but hey, it's cool too)

 

[usp_fan]

You can have a local machinist cut and thread a standard barrel. My 20" bushy barrel got converted to 18" with FH after the ban. I think the charge for cutting, threading and turning the barrel to light profile, and to thread a FAL barrel was $60. The machinist was excited to work on something as cool as a rifle barrel.

--usp_fan

 

[MatthewVanitas]

@ usp_fan:

Did you have to fiddle with the gas system after you cut your 20" back to 18", or did it run great as-is?

Those that have custom 17" carbines: is it just a drop-in rifle-length gas system, or is it tweaked for the 17" barrel?

One downside of going under 20" with rifle length: no more bayonet. Not that it's a big deal, but it does seem tragic somehow.

-MV

 

[Zak Smith]

I know people have just cut down 20's to get to 17 and 18, but I have never measured the port size on my 17".

 

[Zundfolge]

You can have a local machinist cut and thread a standard barrel.

Don't they also have to crown the muzzle? (something a gunsmith would know, but not sure about any old machinist).

 

[gotm4]

Randall Rausch of www.ar15barrels.com does cutting, threading and target crowning of AR barrels for $45 if you have the barrel already off of the upper receiver. His work is 2nd to none.

 

[usp_fan]

Sorry to take so long to get back on this thread. No adjustment was needed to my gas port. Everything from Wolf to high end reloads are cycling fine. As far as crowning, yes, he faced the barrel and I crowned it lightly, but I didn't feel the need for a deep crown b/c I knew a phantom was going on the front to protect the muzzle. I do have to say that $45 is a great deal. Looks like problem solved if he can turn it around fast.

--usp_fan

 

[derek45]

"....Randall Rausch of www.ar15barrels.com ...."

+1

Randall cut My 20" COLT Govt. to 18"

I don't think he opened the gas port, and the gun runs 100%

Price and time were both very satisfactory.

 

[dm1333]

I ended up buying a CMMG upper with the 18 inch barrel and midlength gas system. So far it has swallowed a few hundred rounds of 55 gr. Wolf with no problems, no cleaning and no lube. I want to see just how long it goes before an FTF.