DeHass recommends 4140HT for the receiver body and block. Good materials, they're used regularly to make rifle receivers today. It is the design that limits the Vaultlock to lower pressured cartridges. The Vaultlock uses a round breech block, because it is easier to make a round hole in a home shop than it is to make a square or rectangular hole for the breech block. The Vaultlock was designed for the advanced hobbyist to make in his home shop. There are no pre-inletted stocks for the Vaultlock, so the stock and forearm would need to be designed and made by hand from a blank. In my eyes, the Vaultlock would be a prime candidate for a rimmed cartridge, say a .45-70, a .444 Marlin or a .405 Winchester. I got as far as drilling then reaming the breech block hole, making a breech block for 1 action using a Neidner style fining pin that goes in the block from the front so it can't blow out towards the shooter, and drilling and threading the barrel tenon hole. DeHass uses a 1" barrel thread. I found the 1" thread interferes alot with the breech block on the first one, so I switched to a 15/16" barrel thread on the other 3 that I machined. My plan never envisioned "high pressure" cartridges so I feel confident in the 15/16" barrel thread, that will leave plenty of thickness in the chamber walls. That's as far as I got. I just got so busy earning a living I guess. All my started parts are greased-up and stored so they don't rust. I hope I have time after I retire to finish at least 1 and make a complete rifle out of it. I have a couple of feet of 4142HT (that's 4140 in other shapes than round) bar. I'd sell a chunk if you decide you want to make one. It took me a lot of searching to find suitable materials. Speedy Metals or On-Line Metals has ground and polished 4140HT that'll make breech blocks. That's all I know, which ain't much!!! The round breech block is the weak point and the thru hole. IF a square breech block hole could be made, and the receiver made without the thru hole where the breech block had support at the top, it would be much stronger.