So I weighed one of the 62 grain bullets with the scale, and it was on. I'm going to try 26 grains of powder and a 2.230 COAL tomorrow, and also test some factory loads. I guess I should ask this: do I even need more velocity? Assuming a hunting usage for this cartridge.
You do not need more velocity if your increased powder charges lead to blown, pierced, leaking primers. Gotta tell you, load them hot in cold weather and you will be seeing smoke coming out of the loading port in spring, when those rounds blow primers.
As
@AJC1 said, use factory ammunition as a check. Personally, I am surprised your chronograph works in 30 degree weather as mine would not. If I placed the battery on the vehicle dash and warmed them up to the range, my chronograph would function until the batteries got cold. But, without a "standard", you really don't know if it is your ammunition, the weather, or chronograph misalignment. Or, everything is working as it should and you are getting 2400 fps for real. I don't move too fast in 30 degree weather and neither will your bullets.
With a 20" barrel, if I pushed 68 grain match bullets near 2800 fps, I got pierced primers. I kept my 75 Hornady Match less than 2700 fps or I had problems. Per my chronograph, 73 Berger Moly Coat, Black Hills went 2724 fps. And you have four inches less barrel, maybe what you are seeing is real.
And if it is, I would look real hard at what you are hunting. If it is gophers, it is OK. If it is poodles, maybe the small poodles, but not the French Poodles. All this round has is velocity, and when that is gone, might as well be tossing atlatl's.
So, test the factory ammunition, test your reloads. If you have blown, leaking, pierced primers, cut your loads by a half grain, and continue cutting until all pressure indications go away. And ignore published numbers, or the numbers on your chronograph. What you get will be:
it is what it is.