Can someone tell me about Ar15 mid-length carbine history?

[M4Gunner]

Hi Guys, Just a general history like who made it first & what is the reason behind it. Thanks in advance!

[Robb Jensen]

IIRC it was Armalite that made it first. It was for lower gas pressures (IIRC approx. 9K psi less), slower cyclic rates which results in less port erosion, less extraction problems, longer bolt life and inherent more reliability as it's much closer to the original AR15/M16s gas system length design (rifle length being original).

[KevinB]

Armalite and 5thSFG

IIRC desire was to create a more reliable and longer part lifed carbine with the "sweet spot" of the 16" bbl for velocity in 5.56mm. Transfered into 7.62mm NATO as well.

It also ran into the 6.8 project.

I have no idea of the exact timeline -- KAC had the first "fighting" midlength systems I ever saw... Coldblue can expand on KAC's - who they went to and why - since I always seem to get it wrong.

KAC's and Armalite's middy lengths are slightly different - with KAC's gas system slightly longer in length.

[M4Gunner]

Thanks guys!

[coldblue]

Our mid-length gas tube originated on our SR-25 (7.62x51mm) Battle Rifle.
This "battle rifle" only had a 14.5" barrel, so we pushed the gas port out towards the muzzle until we achieved the port pressure we were looking for.
I am at home right now, or I would measure one of ours and post it, but as stated above, its a little longer than Armalite's "standard" length which originated in a 5.56 gun application.
When we subsequently evolved our 5.56 mid-length carbines years later, we did not want to introduce a forth gas tube length into our inventory system, which was also already stocked with standard rifle and M4 carbine lengths, so we used the same SR-25 Batle Rifle gas tube in their development. However, this also tested very well in 5.56, so we were very happy with this decision, in other words, we could not prove that the "standard" mid-length was any better.
Very soon now you will be able to try these out, as we are getting close to releasing our 16" barrel URX Carbines.

[KevinB]

Very soon now you will be able to try these out, as we are getting close to releasing our 16" barrel URX Carbines.

Thats the news I have been awaiting.

[QuietShootr]

Our mid-length gas tube originated on our SR-25 (7.62x51mm) Battle Rifle.
This "battle rifle" only had a 14.5" barrel, so we pushed the gas port out towards the muzzle until we achieved the port pressure we were looking for.
I am at home right now, or I would measure one of ours and post it, but as stated above, its a little longer than Armalite's "standard" length which originated in a 5.56 gun application.
When we subsequently evolved our 5.56 mid-length carbines years later, we did not want to introduce a forth gas tube length into our inventory system, which was also already stocked with standard rifle and M4 carbine lengths, so we used the same SR-25 Batle Rifle gas tube in their development. However, this also tested very well in 5.56, so we were very happy with this decision, in other words, we could not prove that the "standard" mid-length was any better.
Very soon now you will be able to try these out, as we are getting close to releasing our 16" barrel URX Carbines.

Are the Battle Rifles ever going to be available?

[AR15barrels]

Just a point of reference.
The Armalite mid-length is indeed the industry standard.
If you buy an Armalite, Rock River, Global Tactical, Sabre or CMMG mid-length barrel, these all use the Armalite spec gas tube.

Armalite's spec is carbine + 2.000"