I have both a 6½" and a 4" Model 624 (bought when they were first offered). They both will shoot well under 1" at 25 yards off a rest. I use home cast from a Mihec mould for the H&G #503 (250 gr Keith bullet) cast of WW's + 2% tin sized at .430". Here's my favorite target shot with the 6½" standing at 25 yards:
I hadn't shot it in a while and was doing it in front of witnesses. I couldn't remember if I had sighted it in at 6 o'clock or on center. So, I held on the ten ring for the first shot knowing that regardless how I had it sighted it would give me a ten. When I saw it was shooting dead on I put the rest of the shots in the "X" ring ( I had been shooting exceptionally well for me on the previous couple of targets with another revolver).
This was the ol' Skeeter load (a 250 gr Keith ahead of 7.5 grs. of Unique). That is a great field load, incidentally.
I predict that you will LOVE your new-to-you 624.
Dale53