need a pic

Things I would look at:
Bolt face
Firing pin tip and protrusion
Fit betwixt the two
Clear firing pin channel/main spring
Primer type
Brass type with respect to primer pocket
Flash hole size (reaching a bit)

Not much of the above would explain the 'pin hole at the edge' trouble. Just thinking of things which might affect the firing pin to 'smear' the indentation.

Going from memory (don't have an Arisaka), it's a '98 Mauser-ish design. It should retract the FP upon opening the bolt...at least I'm pretty sure it's cock-on-opening. That should negate any FP hang-up. Hmm...pictures should help.

Ariskas are generally very strong actions of high quality, but they are getting long in the tooth. If he did not have any issues with the factory ammo, I would suspect either his loads are hotter than the factory loads or the primers are softer. The first place I would check would be the bolt face and specifically the fit of the firing pin in the firing pin hole. If there is too much room around the firing pin it can move aside allowing the primer cup to flow into the gap. Have had this experience on older rifles before.

First of all, I won't claim to be an expert on anything, but I have many years experience with ONE particular Arisaka, and lots of reading/research about the things.

Arisakas commonly have oversize chambers; they were made with no regard for reloading. As a military rifle, reliable operation under battlefield conditions was the only consideration, and the cases were one-time-use only. The one I have was built in the mid 1930s and is as finely made as any rifle I have ever seen, but the cases that come out of it look like they were just short of blowing out. Norma factory ammo shows fired primers backed 'way out of the pockets, and a big bulge ahead of the case head. In order to reload for this rifle, I found I had to back the sizing die out until the die shoulder just barely kisses the shoulder of the fired case, and does not push the case shoulder back at all. Then the primers will stay in place. Cases still expand a bunch, but there's enough taper to the case body that the backed-out sizing die will straighten out the bulge. I inspect the cases VERY carefully, and don't figure on reloading them more than five or six times. Have not had one separate, but I stick with mild loads after the first loading.

Many years ago I had a primer cup blow out like that, but it turned out to be from a lot of Remington LR primers that had defective cups. Remington recalled those primers and sent me a whole carton to replace them. I pulled down the ammo I had loaded and popped the primers, and have not had any more problems. It's possible that a similar problem may be present here, but that's a long shot.

Look carefully at your bolt face, and you will likely see a small pit where the primer blew out. If there is more than one pit, It would indicate that the problem is with the primers. If there is just one pit, it's likely that the bolt is not supporting the case head right there.

Hope this helps diagnose the problem. I treasure my old Arisaka because Dad brought it back form Japan in '46, and I sporterized it when I was in college, but it's a cranky old sucker to load for. Shoots good, though.

Catoosa