I have friends that own the 700ML. They did not switch yet to 209's. They found that if they left the bolt cocked the factory spring would weaken and not have as much oomph as when new leading to occasional misfires. I never leave any of my bolt guns cocked in storage. The 209 upgrade kit had a much better spring in it. And I must say that I have no idea which kit the gunsmith installed for me, except that it works really well.