Browning... Varget, RL15, and 4064 all have almost identical burn rates.
Try some IMR4064 or something with a similar burn rate.
And ya gotta be certain that copper is being kept at a resonable level and that you are using good shooting techniques.
QL is predicting IMR4064 should be a great powder for this combo.
Nice velocity and a slightly compressed load to take powder position out of the equation.
RL15 is showing 44,468psi, 2585fps and 92.2% case fill at 42.9gr.
IDK what your book max is on the RL15, but it looks like it could go much higher.
QL says even at 47gr you are still within safe pressure limits.
So, up that charge of RL15, and if that don't work, get some IMR4064
Can I ask why you are staying so low on the powder charge?