I have what looks to be an un-altered Geha shotgun. It doesn't have the breakdown tool on the stock. Instead it has two medallions marked "Geha". The only marking on the receiver is the word Germany. The barrel has the word Nitro with a small mark, possibly a proof mark in front of it. The bolt...
I saw your other reply with the bullet weight. 42.5 is .5 over the listed maximum for both Hodgdon and Sierra's reloading manual. I don't think that's the main cause of the failure though. I'm going to take a guess that the case is defective to fail like that. That's surprising for Lapua.
What you should do is start a new thread of your own. Explain what weapon and give details on the ammo such whether it's a factory loading or a handload. If it's a handload, give us details like bullet, powder charge, primer, OAL.
HS Precision makes replacement bottom metal with detachable magazines that fits the factory Remington BDL stocks. https://shop.hsprecision.com/product-category/parts-accessories/detachable-magazines/
Depending on how well your rifle returns to zero after removing and re-installing the barrel, a receiver mounted aperture sight might work just fine. There are barrel mounted replacement rear sights that have an aperture: https://www.ebay.com/itm/224276392482
I meant to say that I've never done the work myself. I should have proof read before I posted. You could probably just do a search on Youtube and find a video on how to disassemble one of those old Redfields without ruining it.
I have one as a fun gun, but it's real use is as a short range dangerous game cartridge designed for use in Africa. It's not a long range cartridge and definately not an ELR cartridge. That round will just beat your shoulder up and give you no useful practice for your intended goal. You're...