For 'wood screws' I usually use coarse thread machine screws.
They hold extremely well in any hardwood. Most of the Euro (modern) gunmakers use them in butt plate, trigger guard, grip caps, ect.
A pilot hole is needed for each when installing.
#6 is probably the most common size I use for trigger guards, toe plates and other such applications.
I make those from round stock on a lathe. A quick process that allows a head diameter and style to fit what ever countersink size and configuration I may have cut in the piece.
Most often a simple plunge cut with an end mill is what I do so a squared bottom straight sided hole of some standard dia is what I have.
The shank of the new screw gets threaded with a die while still in the lathe.
Leave the head extra 'high' for a rough hacksaw slot, then you can do the extra fitting for a flush or round head and end up with a nice N&S slot if you want to. I doubt many of the makers bothered with that, but sometimes I do, sometimes I don't.
I cut the final screw slot with a simple jewelers saw using a thick width blade. .020 thick gives a nice thin shot then I usually very slightly run a very thin needle file that is Safe on the back side thru the slot to taper the slot very slightly at the top edge.
Not enough to be noticable as a taper, but enough to widen the slot visually so it doesn't look like the screws came off of a Perazzi.
But they are not the Hardware Store size slots that look like they were cut with doubled up hack saw blades.
For the really small screws, a simple 4-40 machine screw thread works good.
A 1/4" to 3/8" thread length will hold just as tight and secure as a coarse tapered wood screw thread in hard wood.
A pilot hole is first drilled for each install and the screws go in easily. I usually use a bit of bar soap on the screw threads for easy install.
I make them the same way.
There are a few places where you can buy machine screws like this with acceptable narrow slots.
They are usually zinc coated but that can disappear quickly with an acid bath or burn it off with a propane torch.
Yes stay up wind of the smoke, it's toxic. So is everything else in life I'm constantly told.
Most of the vendors want a minimum order of a 6 lifetime supply of the things, while we are just looking for a handful.
Aspen Fasteners is one.
So it takes some searching if you want to buy instead of make.
I don't mind making some screws for a build. We are supposed to be Building a Rifle after all.