Primers are very inaccurate when trying determine pressures, especially when trying to compare different brands.
I believe the ones you are using are CCI 250s, especially with as slow a powder, and as much, as you are using.
250s are a hard primer so hold up pretty well under pressure.
Your velocities are a good indication that your pressures are max, though not max enough to hurt anything. A good working max. After accuracy tests, you'll probably be using this rifle for hunting. That's in the winter and at higher altitudes. Pressures will drop a bit, so you'll have fewer problems.
I would drop the charge back by .2 grains...twice. In other words...78.0, 77.8, 77.6, then 78.2, and 78.4, and check the accuracy.
I would probably move the OAL a bit with the same loads. I don't know what the "jump" is, so I would measure THAT, too, so I can judge better.
I would consider the 79.0gr load max, so I would stay below that.
I don't know what the max deviation, or SD, either one, is so I would keep an eye on that as I was shooting.
I am one of those lucky people that can shoot for accuracy and use the chronograph at the same time. FWIW, I use an Oehler M33, that I've had for over 30 years, and checked many times to see that it stays the same.
You've got your load close, so just need to test accuracy.
Have fun, and "eat meat."
Gene