I suspect it will vary quite a bit depending on the particular brand of M855 ammo you are shooting. Some brands to me "feel" weaker than others plus judging by the direction of the ejected brass they can be quite different as well. Unfortunately I don't have a chrono to verify any of this. I've looked into getting a chrono but my home shooting range is in a wooded area and from what I've read not having a clear view of the sky would likely cause problems.