What 300 BLK upper should I buy?

[scooter22]

That is an 8" rail and 9" barrel in the picture. As you can see, the entire threaded portion of the barrel protrudes from the rail. This should mount cans from almost all different manufacturers.

Knowing a carbine length rail is actually around 7.2" you would need an 8.2" barrel to get the same fit. Mid length is 9.2" rail, 10.2" barrel.

Your rifle is either one or a combination of below;
Sig can doesn't sit as far back over the threads
Rail is not actually the full 7.2" carbine length
Barrel is longer than 7.5"

I am not trying to be argumentative, I just want to help people get a combo that works. A barrel 1" longer than the rail is where to start.

I'm failing to see how an 8" rail will work on a 9" barrel, but a 7" rail wouldn't work on an 8" barrel.


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[themonk]

I think his comment is directly related to the KMR. The KRM has half inch ears on the sides so a 8 inch rail is 8.5 inches long which may mess up suppressor clearance depending on your choice of cans/muzzle device.

[Todd.K]

Most carbine rails are called 7" but are actually 7 1/8" to 7 1/4" long.

The KMR wings may even be a bit longer.