Does any thing have to be done if you replace a Sign .40 Barrel with another Sign .40 Barrel. Is it just swap out and go? How many rings required a replacement? I can still see lands and groves. Just purchased a Police trade in. Thanks for looking.

All direct replacement Sig OEM barrels should be just a drop-in. May be some anomalies due to min-max, but rare.

Re a police trade-in. Seriously doubt there would be anything wrong with a police trade-in barrel unless it was rusted. Cops carry a lot and shoot a little, plus most agencies have an armorer.

My own 1995 P229 DA/SA .40 has over 47,000 rounds through it. Everything, including the barrel, look nicely broken-in.

I am sure that is the case. I would like to know if you replace a sig barrel is it just a drop in with out any work from a gun smith.

Yes in all but the rarest cases.

I bought a P226 in 40 S&W and found it was originally a 357 SIG, so I HAD to get a 357 barrel for it. It fit fine and shot well. So as above, unless there is an anomaly it will fit.