Mid-length on 20" AR?


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Marnoot
September 13, 2004, 10:55 AM
Firstly, the original (top) image is from Zak Smith's posting on TFL (http://www.thefiringline.com/forums/showthread.php?t=151827), I hope you don't mind my borrowing for this illustration!
I'm going to be building my first AR-15 here soon. My planned configuration is almost exactly like the one Zak showed in his posting, except I'd like to get a 20" barrel, but want to put mid-length handguards on them as I prefer the way they look. The problem is that I have yet to see another in that configuration.
All AR-15's I've seen with mid-length handguards have them on the shorter 16" barrels. I had my photoshop-adept brother "lengthen" the barrel from Zak's image to about 20" to see what it'd look like.
The bottom image is what I'm thinking of, with perhaps a fluted barrel to shave off some weight. I've already decided I like the way it'll look, my question is whether the shorter handguards on a longer barrel will negatively affect balance? If so, will fluting the barrel counter that? Thanks in advance from an AR-15 newbie! :)

EDIT: Am I going to be able to find a 20" barrel assembly with the gas port at the right position for mid-length? Or would that be something I'd have to get a custom job done on? If so, how much would that be likely to run me?

http://www.marnoot.com/images/ar-15-comparison3.jpg

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Zak Smith
September 13, 2004, 11:34 AM
Hi. Nice photoshop job.

You could probably find someone to build you such a barrel, but it wouldn't be cheap- a barrel blank would have to be drilled special for the mid-length system.

It's important to understand the effects of the gas system type on rifle function and shooting. In a 16" gun, you can choose either the mid-length gas system, or a carbine-length. The advantage of the midlength in a 16" is that the gun will run more reliably due to a gas impulse closer in force and profile to a rifle-length system; secondly, the gun will recoil more smoothly because the gas impulse is less forceful.

In summary, you should always use the longest gas system possible for the barrel length you have. This will enhance reliability and increase subjective shooting factors. In 17-20", use rifle; in 16" use mid, in 11.5-M4, use carbine.

-z

Marnoot
September 13, 2004, 11:47 AM
OK, that makes sense. I guess I'll need to choose between a 16" with mid-length, or a 20" with full-length. I wouldn't be able to afford a custom barrel job, and I guess it would make for a less than reliable gas system. Thanks!

Zak Smith
September 13, 2004, 11:57 AM
Another good choice is a 18" with rifle gas system. These are reasonably common because of the popularity of "SPR" clones. If you get a lightweight barrel profile, it will handle very nicely. The profile under the handguards should be no more than 0.8 or 0.85.

-z

Sleeping Dog
September 13, 2004, 05:41 PM
I wonder ...

If you used a standard 20" barrel like in your picture, and added an additional "sightless" gas block in the correct place for a 20" barrel. You would have to drill the "rear" block for the gas tube to run through, and an inch or two of gas tube would show between the gas blocks, but may not look bad, like the cleaning rod on an AK.

Then the rear gas block would only be there to hold the sight and handguards.

It would be a lot cheaper than a custom barrel. Real cheap to just do it on photoshop to see what it looks like.

Regards.

Marnoot
September 13, 2004, 09:33 PM
Like this (roughly), sleeping dog?

http://www.marnoot.com/images/ar-15-2.jpg

Borrowed the gas tube from a Bushmaster AR pistol pic.

EDIT: Although, isn't the gas block on a 20" barrel already up near the end, with no blocks back where the sight is in this picture?:confused:

Zak Smith
September 13, 2004, 10:08 PM
How much weight is saved on a 20" rifle by using midlength hand guards? Not very much.

In any case, if you used a mid length float tube and a 20 barrel, you could use all stock components.

-z

Sleeping Dog
September 14, 2004, 04:18 PM
That looks pretty good with two gas blocks. The only reason for the rear one is to hold the handguards in place.

Not for me, because with my eyes, I need the front post as far forward as possible. maybe even at the muzzle of a 26" barrel. My eyes are ok, but my arms are too short to hold books. :)

Regards.

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