Animation blend for Tactics FPS

For so long I considered how to blend relevant animations perfectly—while you are aiming down and pulling bolt at the same time.
For example, I shot a rifle, then it automatically reloads: rightly I release my right mouse button to quit ADS, how to make sure your anim-machine is frequent just like general 3A first person shot?
I make myself montages as a Maya user—I can prepare two sequs for idle-pull and ADS-pull.
Could some pioneers share their solutions and demonstrations?

PS:Now I just apply montages before blending ADS state and idle state, not works good.
The follow is the gun I am dealing with. Perhaps a smaller stock side will be a little more esthetical?