Pawpaw40
06-20-2021, 09:18 PM
I loaded up some 450 grain powder coated cast lead bullets for my 45-70 Trapdoor Springfield and took them to the range. They were at the starting load out of the Lyman Cast Bullet book, using Varget. Shot them through the chronograph, and they were averaging 1800 fps, the book said that they should be 1227 fps. No signs of excess pressure, no difficulty extracting, no flattened primers. I went back to the book, and I found where I had the COAL wrong. I had made them 2.545" (2.550 was the COAL for 405 gr. bullet) rather than the 2.850 the 450 gr. bullet required. Pulled the bullets, made one the 2.850 length and tried to chamber it. It will not chamber at that length. I had to take a cleaning rod and knock it out from the muzzle. The bullet had hit the lands and grooves. The bullet is 20 to 1 lead/tin ratio, pretty soft. The bore slugged .458, the bullets measure .4575, I wanted the softer bullet, so they would obdurate to fit the bore. There was no evidence of keyholing. No leading of the bore. It was the Lee #457-450-F mold and the recommended alloy was 10-1
I am confident that the chronograph was reading correctly, I had shot some subsonic 300 BO the same session, and they were as quiet as normal, and velocities were all fairly consistent, for both calibers. I know that powder coating will usually produce higher velocities than hard cast lubed bullets, but not 50% higher, at least not in my experience. In 300 BO it will produce on average about 100 fps, just enough to get it over the speed of sound. I was thinking that the shorter COAL might have raised pressures enough to get the velocities up, and that may still be true, but I have to get it about that length to chamber.
I was thinking about reducing the charge of Varget by 5 grains (below recommended starting load), shooting it over the chronograph, and working the velocities up to around 1400 fps, which is about the middle of the range for that bullet/powder combination, or when the gun groups best, whichever occurs first. And holding to the 2.545 COAL, which I know will chamber. What do you all think?
I am confident that the chronograph was reading correctly, I had shot some subsonic 300 BO the same session, and they were as quiet as normal, and velocities were all fairly consistent, for both calibers. I know that powder coating will usually produce higher velocities than hard cast lubed bullets, but not 50% higher, at least not in my experience. In 300 BO it will produce on average about 100 fps, just enough to get it over the speed of sound. I was thinking that the shorter COAL might have raised pressures enough to get the velocities up, and that may still be true, but I have to get it about that length to chamber.
I was thinking about reducing the charge of Varget by 5 grains (below recommended starting load), shooting it over the chronograph, and working the velocities up to around 1400 fps, which is about the middle of the range for that bullet/powder combination, or when the gun groups best, whichever occurs first. And holding to the 2.545 COAL, which I know will chamber. What do you all think?