Finally got my hands on the new Magpul rail light mount, there's a bracket with rings you can take off so you can mount your surfire scout light right to it. I had to have this for my MR556. But seems you need to remove material to use it with the Tri rail on your ACR. But here it is on my MR556.
Taking out my defibrillator to revive this post. I'm a bit late with the purchase, but i just picked one up. It took some filing to make it fit as far forward on the rail as i wanted it. The handguard cap(useless now that i have a DD Omega rail) was in the way. Looks great. Works awesomely on the AR. It replaced a VTAC mount.