My 1908 house has that in all the windows--except the ones I stupidly removed it before figuring out how to take it out for reuse. Several of mine were a little loose--but when the sash lock was used, they tightened up. If your locks are fitting right, you should be okay....

I haven't had to try this, but what about placing a piece of that bulb-type weatherstripping in the groove--or a piece of felt--maybe even duct tape!?

Hi,
When I install sash that are already loose, I use a heavy cardboard (Ramboard) under the metal as a shim. If the frame is wider at the bottom or middle, you can correct that situation with shims too.
I learned about paper shims under metal weatherstripping on the first old house I worked on (weatherstripped in 1943, according to the workman's signature!)
Casey