Can't tell by your post if you bought this new, new to you, or a "new model."
If you bought it second hand, maybe somebody did hit it with a hammer to knock out a stuck case, like your gunsmith said. These rods will sometimes unscrew a little bit under recoil, causing a bind as it moves forward.
Seen it, and talked to my gunsmith about it, too.
"The man who has fed the chicken every day throughout its life at last wrings its neck instead, showing that more refined views as to the uniformity of nature would have been useful to the chicken." - Bertrand Russell, 1912