Not sure why I found this so interesting, but here is what I have fund out. None of this information is mine, but I've included links so you can determine if the source is trustworthy, should you too be interested.
0 buckshot diameter .320 which happens to be the shot size closest to .308 without going under.
----------------------------------------------------------------------------------------------------------------------------
3gr Unique 0 buckshot sized with a Brown Bear steel case 1030fps
http://www.youtube.com/watch?v=LJMLuQQ45QM--------------------------------------------------------------------------------------------------------------------------
The Buckshot Option
Even more versatility may be derived in .30-caliber rifles by substituting a single 0-Buckshot round lead ball for a more conventional bullet. (A single 0-Buck round lead ball weighs is .32-inch in diameter and weighs 48 grains.) A charge of 3.0 grains of Bullseye powder is usually suggested, topped by a tuft of Dacron of Kapok fiber and then the lead ball. This comes close to replicating what the old Lyman handbooks called "the ideal cellar and small-game load," and is suitable for most of the major .30-caliber rifles (including the .30-’06 Springfield, .308 Winchester, .30-30 Winchester, .300 Savage, and .30-40 Krag).
http://www.woodsdrummer.com/ml07.html-------------------------------------------------------------------------------------------------------------------------------------
For a really inexpensive 25 yd plinking load try using a 0 buck shot pellet lightly lubed with Lee "Liquid Alox" and press fitted half way into the mouth of neck sized .30 cal cartridge on top of 3.0 gr of Bullseye. Because of the small charge you should elevate the muzzle before firing to move the powder next to the primer. A pound of Bullseye and a bag of 0 buck will keep you in plinking ammo for a long time. A variation on this load is made by using a 00 buck pellet seated on top of a .30 cal gas check and run through a .308 bullet swaging die on your luber/sizer.
http://www.frfrogspad.com/miscellg.htm#practice--------------------------------------------------------------------------------------------------------------------------------------------
3. The Buckshot Option
a. 30-caliber rifles loaded with a single 0-Buckshot, .32-inch diameter, 48 gr., round lead ball.
b. 3.0 grains of Bullseye powder with Dacron of Kapok fiber and then the lead ball.
c. called "the ideal cellar and small-game load," and is suitable for most of the major .30-caliber rifles (including the .30-’06 Springfield, .308 Winchester, .30-30 Winchester, .300 Savage, and .30-40 Krag).
http://www.survivalistboards.com/showthread.php?t=1855A lot of other info on low power .30 caliber loads at that link, including one described as "almost silent" shooting a 220gr bullet.--------------------------------------------------------------------------------------------------------------------------------------------
Just thought I'd share something cool I learned from a friend. You can have a fairly effective small game rifle by using a .30 caliber rifle and single 0 buckshot. The "recipe" is to use a 22lr case to charge the 30 caliber case with bullseye powder and place the ball by hand into the case, resizing not necessary. Apparently leading issues are negated by the extremely low velocities. Should hit POA out to 50 yards and is extremely quiet. I'm not an expert, try at your own risk
http://www.missouriwhitetails.com/forums/viewthread.php?action=printable&fid=41&tid=140487Picture of the loading setup (similar to what was in the video Whit posted)