SMT Mike, I use a small drill at the bottom of the head and I've not had issues with shavings. I use MoI heft match not swing weight heft match and if I need a special weight head lighter/heavier I order it from the vendor hand pick. I also think you are correct about small gains in a few grams as to changing CG. One would have to add a lot to move CG. Most of the adjustable heads with all the gizmo's are just marketing. Loft, face angle open/closed are the only ways to effect ball flight. The gizmo heads don't have enough weight to effect ball flight. See Cochran and Stobbs. Dave Tutelman's website has more info. that Dave did very well at explaining.
In the old days we used a small hole in the persimmon head sole with lead or now tungsten powder. More modern persimmon heads now have a designed in port.
TheBlade Can you post or send me what type of gun you use?
This the type I use but I have one where I can change nozzle size and use a very small nozzle I don't go thru the plastic plug but through the sole. https://www.hotmelt.com/products/advanced-hot-melt-golf-club-weighting-kit-gun-and-cartridge
