A few months ago, I decided to develop cast bullet hunting loads for a few of my rifles. I cast 30 cal and 458 cal bullets to use in 30.06, 308, 30-30, 30-40, and 45-70. All bullets are gas checked and powder coated. Early work was for plinking loads and they all worked beautifully. Then I started pushing velocities up to the 2000 fps +/- range on the 30 cals. Bullet selected was the RCBS 180 gr FN because of it's healthy meplat.
The 30-30 (Winchester M54) and the 308 (Rem M600) did beautifully, 2050 fps for the 30-30 and 1950 fps for the 308. Accuracy is well within acceptable boundaries for the range I might shoot a whitetail. The 30-40 does as well as can be expected with it's peep sight and my 71 yr old eyes.
The 30.06, a sporterized 03A3 with a WWII 4 groove bbl, refuses to give any kind of consistent accuracy at the desired velocity. I have tried a half dozen different powders recommended for that caliber and velocity and just can't get there. I tried again this morning with two more loadings and I'd get 2 shots kinda sorta OK and then 2 or 3 scattered out 3-5 inches.
Got to wondering if my rifle and/or scope had gone on the fritz, so I grabbed a 50 round box of the plinkers loaded 2-3 months ago. It is the RCBS bullet over 16 gr of 2400, straight out of Harris' "The Load". I fired 9 shots at a steady pace over about a 10 minute period. The first 5 went into a little over an inch and the other 4 into 1.3". Obviously nothing wrong with the rifle.
Any ideas why this bullet does so well at plinking and hunting velocities in 2 calibers and so well with plinking but lousy with hunting velocity with a third caliber. I just don't understand. Do some barrels just hate higher velocities with cast? BTW, this 03A3 has always shot well with jacketed. In fact, I made my longest ever kill with it a few years ago, about 325 yards.