Improving velocity consistency

[Orchemo]

New to BP shooting. I have a pair of Lyman Deerfield rifles. One in 54 and one in 50.

Been shooting a couple times a week at the range in preparation for an upcoming elk hunt.

Using my Garmin chrono and getting swings in velocity measurements.

My 54 PRB load is 90gr of Triple 7 3F. Gets me right at 1700 + fps.

Between each shot, I run a spit wet patch, then a dry patch.

I took the 90gr of volumetric powder and found it to be 75 gr by weight. Made up 15 tubes of powder at 75gr weight. Comfortable that powder charges are consistent.

CCI caps are new and same tin.

Seems the first 3 or 4 shots are consistent, but then more velocity variation.

What can I improve on?

 

[RobertIN]

What is your SD and ES?

 

[Orchemo]

I think I found my problem. I opened a new box of RB today. They are 0.530
Last week, they were 0.535

Last week,
I was getting 1746 FPS
ES 52
SD 16

Today my WS was closer to 150

Also ran out of 54 cal lubed patches and used 45-50 cal patches today

Will order more patches and RB from the Gun Works in Eugene tomorrow.

Second question: I have an older box of Speer 0.535 RB. Any advantage of Speer vs Hornady TB?