Gave my 357 Henry a workout today. I made up 50 rounds, 158 grain Hornady JHP, 16.7 grains of H110. Book velocity was 1700+ fps. Shot in 5 groups of 10 each all pretty fast. Barrel was HOT! Each group was shooting 1/2" below the the previous. 1st group tore out the center (50 yards). The last group was 2.5" low with more deviation.

Anyone else see this with a big boy?

Mike

I never had to shoot 50 rounds of full strength 357 as fast as I could
while doing test with my magnums.

Three tens was the maximum that I have done in the last five years.

Being a old rifle shooter I will let the barrel cool, if possible
to keep my groups tight and get minimum ES.

I would say that gravity was taking over, with that hot barrel.

Did you turn it upside down, to let it cool down ?

If the magazine tube is screwed into the receiver it's likely that as the barrel gets longer due to heating the cooler magazine tube will sort of "tug" on the barrel and actually pull it down a tiny bit. I have a Ruger Gunsite Scout rifle and the short mounting rail will actually caused the rifle to string vertically as the barrel heats up. If I remove that rail and the handgun scope mounted to it and use the iron sights my groups will get bigger due to old eyes and somewhat ragged sight alignment but they tend to stay centered. BTW, I expect that this explanation is way over simplified and what is happening is how the barrel "vibrates" when a bullet is passing though it but for this old geezer I've found simple explanations a lot easier to think about.

I wasn't doing rapid fire. I was just shooting 5 magazine loads at a leisurely , but steady, pace. I was taking time to accurately aim. Time between shots probably 7 or 8 seconds.

Barrel got hot. Your "pace" was enough to keep it hot and allow it to maybe droop a bit.
Or cause a change in POI for whatever reason.
For hunting, you're not gonna shoot more than couple each time. For target, slow down.
At least it is only vertical spread. lol