Picked up a M57 Yugoslavian TOK, Lee 3 die set, collet die, and some Starline brass. Slugged the barrel at muzzle, groove to groove .313, and land to land (bore) .304. NOTE, that's .304, not .300. At chamber I got the same measurements as at the muzzle. Measured some factory ammo, S&B bullet diameter at .3075. and this is the stuff that is supposedly leaving the barrel at around 1,700 fps. My objective for this project is to develop a lower pressure economical lead bullet practice load, which if accurate enough could be used for 25 - 50 yard plinking and perhaps target shooting and small game hunting. So I am first working with the Lee .32 pistol bullet - .311 2R 100 grain bare based bullet cast from basically wheel weights, water quenched. These run a little softer than the standard Lyman #2 alloy, but are close. I've used this bullet extensively in .303 British reduced loads with great success shot as cast and lubed with liquid Alox, managing 1 hole groups at 50 yards. This is also a good bullet in .308 and 30/30 Winchester reduced loads. These bullets in this alloy weigh in right at 100 grains after lubing. My notes on OAL are MIA at the moment, but I am loading the case mouth to the middle of the middle driving band of the bullet. The bullets in my first trials were all .310, just to make sure and avoid any constricted neck issues that others have mentioned when using larger diameter bullets. I have not done a chamber cast, but am testing various diameter bullets loaded in dummy rounds for fit in the barrel. I have no problems with .311 diameter bullets loaded in the Starline brass. My first powder to work with is Alliant Red Dot, for which there is absolutely no booked reloading data that I can locate for this round. I started at THREE grains and worked up in 1/10th of a grain increments seeking reliable functioning of the M57. At 3.6 grains I was getting 50% case ejection, at 3.7 grains I got full case ejection on every round, but they are coming straight back at me just above my head. The testing has all been done at 10 yards starting out, and the groups have been less than stellar and low and left 3" from the center bull, and getting about a 3" group on average. I am firing from a ad hoc table rest for stability. There is very light leading in the barrel after shooting which is easily brushed out during cleaning. I have no crony at the moment, so everything is proceeding slowly and carefully My next test loading is using .311 diameter bullets, hand lubed with Hornady Alox in the bottom case enclosed lube groove, and a measured 3.65 grains of Red Dot, dropping back a bit to see if I can get more side ejection as I did on the half that did eject when testing at 3.6 grains of Red Dot, as they tended to just pop out the side of the pistol and not travel far. I will report my findings as this testing continues, and would enjoy hearing from anybody on their experiences reloading this cartridge with cast bullets.