There are three ways to shoot cast. First is cast, like cast, at what are considered to be cast velocities using faster powders. The second method is to use cast pressures, but go to slow powders and allow lighter per caliber weight bullets to accelerate slowly using slower powders. The third method is to harden cast bullets and raise the pressure so that the base of the bullet can withstand higher pressure.
I always shoot using the second method so that I can keep my bullets soft. I shoot rifles with throats shaped to support a softer bullet. The advantages of using this method are a soft bullet for hunting and a less base expanding pressure to create bore friction. The less bore friction you have, the less barrel vibration you have. The less barrel vibration you create, the wider your accuracy nodes will be and you can usually achieve superior accuracy at this point.
There are two things that work against you when you want to shoot low pressure / high velocity loads:
1. First is bullet weight. This is because all weight is additive to increase inertia and thus pressure on the base.
2. The second negative is short barrel length because it removes options to achieve velocity without raising pressure.
There is one saving grace. Case volume. Increasing volume slows the expansion of powder gases until the bullet is moving in the bore where it is fully supported. ZThe larger the case, the farther the peak pressure is pushed down the bore. Thus the bullet is moving faster when it occurs and can handle more pressure before the base is changed.
So what you have is an under bore cartridge (30/30) normally described as efficient. You are trying to use a heavy for cartridge for caliber bullet. And you have a short barrel. Grumpy, you need to explore the third method of shooting cast and in my opinion are heading in the right direction by increasing hardness.