What rifle does it fit?

[BigBronco]

Can someone ID this mag? I am stumped. There are no markings on it. Very unusual design. Similar to the one for a Ruger scout but different.

[6mmintl]

None, Anti tank SMAW mag

[ducky_0811]

Bonus question, what is the load for the spotting round it shoots

[BigBronco]

At first I thought 6mmintl's answer was worthy of OT. A mag for a rocket launcher, really? I googled the SWAW and learnd a thing or two.

I had hoped to put this mag on Fleabay however I doubt any of us standard gun guys would be allowed by the powers that be to actually own one. So I stand corrected and Calguns guys come through again.

[Thorax]

As far as I know a SMAW is a shoulder fired rocket and does not use a magazine of any sort

Unless you're meaning the spotting rifle for it, which is a 9mm tracer and not a SMAW round. Now that I can see.
It also looks very similar to a BAR 30-06 mag.

[ducky_0811]

Correct, 9mm tracer projectile in a modified 7.62 nato casing using a .22 hornet propellant. Ballistically equivalent to the HE rockets trajectory. At least that's what my last boss at my recruiting station told me, he was an anti tank assault man.