What do you call this configuration? (pics and description included)

General Firearms NFA
1

I’ve noticed a class of carbines and I was wondering about their origin, usage, and possibly their name.

They usually have the following characteristics:

  • Short barrel – usually 10 or 11.5 inches.
  • Railed forend with a low-profile gas block.
  • Flip-up front and rear sights.
  • Reliance primarily on a red-dot-sight – usually an Aimpoint H1 or T1.

I think the first rifle I saw in this configuration is in the Magpul AoTC videos.

Where did this configuration originate? Is it used by any branch of the military? What is the purpose of this configuration?

If this configuration doesn’t have a name, I think it occurs often enough to merit one.

Here are a few of the many examples:




2

The Navy uses a carbine called a Mk. 18, with several Mod’s, that those carbines are basically clones of.

10.5" barrel, rail.

LMT sells uppers to the Navy.

3

Perfect answer! Wikipedia as a great page on the Mk. 18 CQB Receiver.

Thank you!

4

I don’t disagree with Templar but several of those rifles are what I see referred to specifically as the “Costa” setup. 11.5" SBR with the KAC URX rail and the KAC Triple-Tap muzzle device. Pictures 1, 3, and 4, specifically.

Most of those MK18s shown still have the standard FSB, although I believe the newest iteration with the Daniel Defense MK18 RIS II has a flip-up front and long rail.

The move towards longer rails covering the gas block comes from a trend in grip/stance that pushes the hand further out towards the muzzle – the long rail allows the grip to move out and protects it from getting burnt on the hot gas block/sight.

5

Yes – I recognize Chris Costa’s influence. Did he come up with this configuration himself and what would you say is the minimum you need to have a “Costa” setup?

6

I honestly don’t know, and don’t want to presume too much, lest I be smote in the night by renegade facial hair…

But anecdotally it appears to me that specifically the “Costa” upper is the 11.5 with mid-length URX (URX II?) with the integral flip-up front and a flip up rear, with the the Triple-tap brake and an Aimpoint micro. Bonus points for the Boresight Solutions textured KAC rail panels :wink:

Grant was putting together some “Costa uppers” a while back based on BCMs and that’s how they were put together, IIRC. Chris’s original upper may have been all KAC? I can’t remember, I’m sure I’ve read about it somewhere on here.

7

I am sure that Templar was referring to the “basic” style and not the individual parts that make it up. Especially considering that the KAC TAP is new to the market. IIRC most of the other mods (no FSB, etc…) are things that started to morph out of the civilian side.

8

For sure, and it wasn’t my intent to contradict Templar but rather build on some of the specific details the OP mentioned.

9

I call them “short barreled ARs”

10

10-4. They aren’t attributed to anyone. They are as a result of enduser’s differing needs and what various people built as a result of those needs as well as other builders emulating them because they looked sharp and heck, they worked.