That's a light plinking load. With your bullet weight, it's probably in the 1300-1400 fps range from a 24" barrel. About 15,000 psi. How much more you can take depends on how hard your bullets are? They'll strip or start leading before you get to maximum safe pressure with Unique. 12 grains will get you to 24,000 psi and 1600 fps. 13 grains to 27,000 psi and 1700 fps. It's all very approximate because case capacities vary with the brand, but you'll be plenty safe within that range. If you want to shoot faster, then it'll be time for really hard bullets and a different powder. IMR 4227, perhaps. 27 grains of 4227 will give the same peak pressure as 13 grains of unique, but the extra gas it makes will bump velocity to the 2100 fps range.
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