just bought a new m&p 15-22 friday,will the flash hider screw off ? I have a gemtech outback I would like to try on it.

Yep. Any 1/2 X 28 thread device will fit.

The best thing to do is to secure the barrel in a vice using a set of vice jaws Link, then use an adjustable wrench to loosen the flash hider.

Note: do not secure the upper in a vice thinking that will suffice to hold the barrel because you will ruin your upper.

I didn't have a set of vice jaws when I removed my stock flash hider. I used two Sure Grip hand clamps with rubber jaws to secure the barrel before I removed the flash hider. I used a long handle adjustable wrench and it didn't take much to pop it loose. The new hider only needs to be hand tight. From that point on, swapping between devices is simple.