Here is my answer (from my exact same experience) from receiving a .30 VP a few weeks ago and owning a .22 Maverick Sniper for a year. I also struggled with tuning at first, on both, but I have learned a lot about the platform in the last year, and quickly was able to get the .30 VP sorted out.
Anywho -The VPs are coming with a 12g hammer, confirmed on both mine and my friend's new .30 VPs we received in the last few weeks. Unfortunately this will not be enough hammer weight to smack that valve open at 150 bar. You need a 13g hammer weight. You do not need a dual transfer port. You do not need a stronger hammer spring. You don't even need the slug probe (I just used the stock probe for now).
Now, your two real options for getting a 13.25g hammer are either 1) buy the FX Maverick Slug Power kit solely for that hammer; or 2) buy the Huma hammer weight kit (13.25g & 14.5g), which I'd recommend as the better option. Myhighpressureair.com has them in stock.
To get the exact power you are looking for I simply set my regs to 175/150, PW7, HS 6mm out, 13.25g hammer weight. Seems 175/150 or 180/150 is the sweet spot for the 30's if you want to make pretty high power.Â
I documented what I did in this thread, if it helps:
https://www.airgunnation.com/topic/maverick-vp-in-30-my-2nd-maverick-now-gimme-a-tune-bois/ I also received the Huma slug/pin probe with my kit which I think I will end up doing a video on, pitting it up against the stock probe to compare if it actually adds any power. But for now, only the 13.25g hammer was needed
Hope that helps.Â