Using 300 smk/RE33/lapua brass/Fed 215- bullet .010 off lands

I anneal every firing. Maybe not annealing enough?

I ran this combo in my factory barrel and was quite accurate. Running the same combo in my new Shilen select match and seems to be shooting some wild velocities, and accuracy reflects it.

Shot 1 3/4" group at 500 the other day. Reloaded same thing up to confirm I was g2g. Shot last night and shot over 6" at same distance. Didn't have a chrony with last night but 2 shots were bout 1 1/2" apart, other was 6" high. What I'm noticing is even .3 grains in powder is the difference between 8" and 3" groups at 500. Never seen a barrel fluctuate so much in that small of a difference

Anybody experienced this with any rifles that could shed some light here.

I'm Gona back the bullets off the lands to .015. Also have some retumbo powder to try.

Feel free to share some load data with a similar combo as well, thank you

I should add I was using cci 250 in my factory barrel. But ran out and switched to the Feds