Mossberg slug gun zero and heat question

[soup]

The past few years I've been using a Mossberg 500 20ga for deer and swapping barrels to the smooth bore for small game. I went to sight in the gun again this year and my first shot was 3" low at 50 yards the next few shots were in semi decent groups around the first. I had to adjust the scope this time to get it to tight groups at 50 yards right on the center of the target. I haven't had to do this in the past. I know it had been bounced around a few times in the safe when it was off the gun. Do these normally keep zero well when swapping barrels or should I leave it be until after Deer season?

The other question was that I was just curious how heat of shooting multiple rounds will affect the accuracy of my shotgun. I may be over thinking this but who knows...

After adjusting the sight I was keeping everything in a nice 1.5" circle at 50 yards. I was shooting one round, walking down range and marking it coming back shooting another and walking back again. I shot 20 rounds through it today (which is not only a lot but kind of pricey) The groups were right where they should be and nice and tight. being that I was shooting the gun for a while I'm sure the barrel was pretty warm.

With that said, will a cold barrel (during hunting season) negatively effect my accuracy enough to warrant any adjustment on my part?
Thanks,
Anthony

[ROCKFISH]

I would not expect a problem shooting in cold weather at deer size game at 50 yards. Provided you do your part.