Answer to a second email question, yes, the finished Browning BLR will be equipped with a sling, almost certainly from Andy's Leather (visit him on FaceBook). In addition to being one of the great leatherworkers in America, Andy maintains the Scout Rifle Community. A sling is a rifle's holster, and any "working" rifle (i.e., one that's not shot exclusively off the bench or in a competition that doesn't not requite the rifle be carried out of the hand (cowboy, for instance) needs a sling.
Obviously, a lot of my thinking on the BLR derives from Col. Jeff Cooper's Scout rifle concepts, although as I noted earlier the concept of a forward-mounted scope is hardly original to Cooper. Andy has been instrumental in promoting and expanding on the Scout rifle concept; in fact, the BLR has figured prominently in several threads.
You guys know I'm a huge fan of the Ruger Gunsite Scout .308...I have more rounds through that rifle than any other bolt gun I own. I've shot it in classes at distances from contact to 400 yards. When I decided to go to Africa, I went with the Guide Gun specifically because I could configure it exactly the same as the GSR (LOP, sling), with the exception of a forward-mounted scope.
The Jeff Cooper Edition Steyr Scout
I always thought the Scout concept was interesting, but I didn't become an evangelist until, a couple of years before the Colonel died, he loaned me his personal Steyr Scout .308 (I believe fitted with the Leupold 2.5X) to shoot through the Gunsite African game hunting class with Il Ling New. By the time I finished the course, I was sold.
The Burris fixed power on GSR sits about 3/4 inch ahead of the ejection port, which is, to me, ideal. Notice that on the Steyr Scout the scope sits just slightly in front of the ejection port. The Leupold variable I handled and shot was mounted similarly. I have one of the new Burris 2-7X Scouts, but I haven't had time to mount it yet.
Could you use the BLR for this intended purpose (non-permissive jurisdictions) out of the box? Absolutely. Remember, I'm going for as light as possible for a travel gun. The trigger on mine is not bad, in the 6-7 pound range; the OL length is 40 inches with the 20-inch barrel (Cooper's Scout rifle standard was 1 meter in length, 39.4 inches); weight is 6 pounds 8 ounces with irons (Cooper's standard was 6.6 pounds - 7.7 pounds with irons and optic). By comparison, the Ruger Gunsite Scout weights in at 7 pounds with irons and a forward scope mount and a 38-inch length. The BLR does need sling swivels, but nothing is perfect.
If I was going to use the BLR out of the box with traditional mount optics I would go for the superb Leupold 1.5-4X 20mm, a great underrated scope weighing in at under 10 ounces, or something like the Burris MTAC 1-4X.
RE: Calibers...take your choice. I agree that .243 might be a good option...lots of different load availability (although no dedicated tactical rounds, I believe...I would go with the Hornady Superformance 95-gr SST), recoil on par with the .223 and a good hunting cartridge in jurisdictions where the .223 is prohibited for deer-sized game. If you don't have a .308, then that'd be the way to go. I have a good friend who travels a lot as an instructor and he routinely brings a takedown .308 BLR.