Cracks in brass

A guy I work with showed me these two brass for his 45-70. He bought the brass new and these cracked on the first shot. The head stamp is W-W. Has anyone got any idea what happened? Here's the info he gave me.

Marvin 1895 in gov 45-70
New brass only shot this once
CCI 200 primer
44g IMR 4198 powder
350g Hornady RN .458 bullet
38 out of 40 cases OK
Reload data from www.realguns.com/loads/45-70.htm

The crack in each case are about identical. Any ideas what happened?
If I do this right, here's a picture.

What do the primers look like?

Here's the primers.

Is it in the same spot in the chamber ? If so check the chamber, if not. Try different brass.....

Two thoughts if the brass is to blame, by far a more common problem than the firearm.

One likely solution is that though the brass had never been previously loaded, it was still not new brass. It hardens over time, and environmental factors present during storage can hasten the process.
It may also have been over hard from improper annealing after forming: a bad lot of brass that got by QC.
Switching to another lot of brass by the same or different maker will clear up the problem if either or both of those causes is at the root of it.

If it's the firearm, it may have a poorly reamed or bulged chamber. Not likely, but it does happen and a chamber cast can confirm or eliminate the possibility.

i have heard some reports of some bad brass from winchester in the last year.
i think they got an improperly alloyed batch of brass..
not all of the cases in each batch were bad, just some of them were.
i'd try and call winchester and have the bag handy.
if you have a bad chamber you'll know it by the bulged mishaped brass.
the cut brass may have also put a cut in the chamber.

I would have to say those primers look fine. They certainly don't look like over-pressure to me.

There is minimal flame cutting on the cracks in the brass. Looks like a bad batch of brass, I had a bunch of Remington brass that would split 1 out of every 5 cases with 26.0 2400 and a 405 bullet.

Definitely some bad brass. Looks more like a burn out than a crack. I once had a batch if Federal .38 Spl. ammo that did that. Not even reloads but factory ammo. I'd give Winchester a call and tell them what the problem is. You'll probably have to send it back but odds are they'll replace the brass for you. I'm guessing the case walls arethinner than they should be on that lot of brass. Could even be a recall because of the problem.
Paul B.

First time I had this was with Winchester brass in 1965 with some 3036 ammo I'd bought. Got a faceful of gas that let me know I had problems. I've seen it and had the problem. I've read and cannot say which is correct that it is due to hard brass of bad annealing. My solution is to discard those and but some new brass. John Hayslio

One could mark the brass at 12 0'clock with a Sharpie and test fire.
I do like the idea of chamber cast.
Brass which is brittle will do this. That's the case for non-nickle plated cases due to nickle not being malleable as a result of multiple reloads.
Primer exhibits LOW pressure, a good thing.
Does Winchester even have phone based customer service?