HV Cast always stirs a debate and I wanted to ask myself why? My experience comes down to experience at pushing soft lead to do more before I harden. That's how I found it. Now how does "my" thought process work?
I have explained the wine glass theory many times. The harder you push, the greater the volume and the faster you go, the higher the pitch or vibration. That's our barrel. At cast velocities, pressure is low and vibration is minimized, so cast accuracy is easy and available across a wide spectrum. Well guess what. It's the same with jacketed. It's just that we don't waste jacketed for this purpose. And most casters don't waste lead when they have jacketed available. Because of this many develop a false RPM limit theory. So, both grounds go unexplored which would make ALL of this easier to understand.
With jacketed we all pretty much realize the our barrel vibrates and we tune the load to exit the barrel at the same point in this cycle. Then we learn that if we fire at a higher or slower rate and warm our barrel that our groups are gonna change probably for the worse, but sometimes better. I find the EXACT same with cast. No difference. Except that we have another variable to account for here. Lube and bullet hardness work hand in hand to control friction and thus the oscillation rate of my barrel. The difference in my thought process between jacketed and cast is 180 degrees opposite.
With jacketed I don't have to concern myself with my bullet and I just strive to get consistent ignition and barrel times to produce good accuracy. With cast, I must think of my bullet and I tune the barrel oscillation to the limit my bullet will withstand. There are a whole host of tricks here that do that and EVERY .... SINGLE .... ONE are designed to control pressure. Not RPMs.
The faster the twist rate, the more resistance the bullet will have to forward motion. The heavier the bullet, the more resistance to forward motion. The smaller the case capacity the faster pressure is going to come up. All of these will raise pressure and lower the options available for top end velocity for cast. Jacketed guys knew this for years. So when they wanted more velocity than a 30/30 could produce, they built a larger case to elongate the pressure curve. In my mind, I do the same. I know that everyone here knows this. What I am trying to show is how I approach it so you can understand my thought processes. RPMs for me are simply a coincidence that as velocity goes up, so do RPMS. Just like the sun coming up every day.
There are three ways to shoot cast. First, is shooting cast at low pressure with fast powders. Pressure rises immediately and begins to drop so the bullet coasts on out. That causes less barrel vibration as it travels out the tube.
The next method I used to list last and that is to mold hard and simply raise the pressure to what the bullet will withstand. Match the hardness to the pressure. But the problem there is that logic only gets you so far if you can't reach the next harmonic node. You reach a limit. Your accuracy doesn't, so you say, RPMs got me when it was really barrel vibration or bullet deformation that stopped you. Harmonics simply made it more difficult.
The third way is to shoot softer cast at the same pressures as in the first method, but to bring the pressure curve up slowly. The exact same logic used with larger case capacities for jacketed. This is the key step. If you have shot cast using methods one and two and believe in them wholeheartedly, then you will have difficulty with this thought process. This is where the game is won or lost. You learn to use lube and hardness together to .... tune "THE BARREL" to the load. Sometimes, the key can be to go to a SOFTER metal to tune friction and bring the barrel to the load.
Sometimes you may not have enough drive area from the lands to do this. That can be too short of rifling or too few of rifling. TOO wide of rifling can be just as much an impediment to forward motion as too fast of a twist. Sometimes your barrel may just not have the interior finish to do this. So I have guns that do put lower limits on me. By that I mean, I can only go so soft before the game ends and I don't have a wide enough window with which to operate with. Then I have to change variables and maybe go to a lighter bullet yet.
To be continued: