Grok patter to remove trailing milliseconds

[newmember]

Two record formats that start a multiline event, what grok statement might I use to keep the milliseconds and set the time as the @timestamp field? Maybe I have to drop the milliseconds?

Thank you

23:29:53.425: Sending [0,UDP] 467 bytes to 10.80.131.7:5060 >>>>>
@23:29:53.425: Sending [0,UDP] 467 bytes to 10.80.131.7:5060 >>>>>

I have been all over the map trying different regex and grok ideas:
^(@)?(?[^:]):(?[^:]):(?[^.]*)
(?!<[0-9])%{HOUR}:%{MINUTE}(?::%{SECOND})(?![0-9])
TIMESTAMP_ISO8601
etc

[matw (Matthias Wilhelm)]

Where are you using those grok patterns (Logstash)? Because we've got a nice channel for that

[newmember]

In kabana.