Thread: Has anyone had this problem?

Sounds like different batches of powder to me.

Other thing to consider is if there were major differences in atmospherics between when you shot last and this test.

What you want to record for a barrel is the muzzle velocity for a particular powder batch / weight combo.

When you get a new batch, load some test rounds to make sure you are still in the velocity band that worked previously (called a node).

Depending on how much you shoot, buying powder in bulk is well worth it for consistent results. For fullbore I tend to buy powder in 4kg bottles, and that is not exactly a busy season...