oinco brings up a great point, in the reloading aspect. I am just getting into reloading and have not experimented with load lengths at this point, so I have not even taken this into consideration. Although if I am correct and you are going to be running .243 out of a .308 magazine you should have a little more room to play with as far as OAL goes anyways.

I don't have any experience personally or know of anyone who runs the HS precision DBM, but I know they don't use the AI mags they use their own magazine design. If you are set on getting a DBM system, as stated by others I would opt for something that takes the AI mags. All of the DBM systems seem to cost around the same amount $280-$320(some go up from there), the CDI mentioned earlier looks to be the least expensive but most of the others come with one magazine, so if you add the cost of a magazine you will be right in line with almost all of the others. It's really up to personal preference at that point. You should maybe contact some local smiths, maybe there is one that takes less work to install? Maybe even call B&C and see if they have heard anything, or have suggestions on which route to go or what mates to their stocks the best (I have to think the aluminum chassis would make it slightly more difficult to inlet for any system)?

Do some research before you buy and keep an eye out on this and other forums, every now and then a deal pops up. I got my M5 with a 10 round mag both unused for well below what they sell for on popular sites from a private party. Good luck and keep us posted on anything you find out or what you end up going with.