There are a lot of variables at work and many reasons a stock could break, so in my opinion it is difficult to fully answer your question. I do not have extensive experience with big bores, but I have seen and repaired broken stocks. Bedding could indeed help guard against certain types of stock breakage, for example if the recoil lug or lugs are not bearing properly on the stock the rear tang or action bolts could split the stock on recoil. By properly bedding the recoil lug/lugs and clearancing the tang this risk is minimized. Bedding wont solve every issue though, even if the recoil lugs are bearing evenly, the wood can flex and split if not properly reinforced. Crossbolts can help immensely and I would personally add them on any wood stocked rifle of .375 and up. The rear crossbolt guards against the wood spreading and flexing alongside the magazine well, trigger inlet, and rearwards, and the front crossbolt guards against the wood spreading and splitting at the recoil lug. On wrists, improper grain flow can make them susceptible to breakage. On my .375 Mauser I just restocked, I added a 3/8 inch grade 8 bolt set in epoxy through the wrist prior to installing grip cap. This stock has excellent grain flow through the wrist, but is rather slender so I added the rod for insurance. I also added front and rear crossbolts. I am surprised your 550 doesn't have crossbolts. Every large bore 550 I have seen have front and rear crossbolts, so if yours doesn't I would definitely add them. I am not sure how the double rifles buttstocks are fit, but if I were doing it they would be glass bedded as well. What I mean by that is my skill at inletting is not such that I would trust the receiver to bear properly and evenly without bedding. I have glass bedded multiple buttstocks to receivers, for example Ruger No 1s and a Marlin 45-70. The Marlin has had 400 grain bullets at 2060 FPS through it with no stock cracking issues. Not equivalent to the Lott or other heavy hitters, but the Marlin is a much lighter rifle and I believe if buttstock fit wasn't proper it would crack or split with these loads. I am interested to hear from those with experience on heavy double rifles, because I have wondered the same thing.