Re: what tap to use?
Yeah, I'd certainly go with the 48 pitch for a stronger thread engagement.
Brownells.com will sell you the taps all the day long.
FYI- a "taper tap" is easier to get started and going straight because it has a tapered point to it. BUT it will not come close to cutting threads all the way to the bottom of a blind hole (a blind hole is one that does not go all the way through)
A plug tap has just a little taper to it but near as much as a taper tap.
A bottom tap has almost no taper but will cut threads practically to the bottom of a blind hole. It is used when you have got a good start with one of the above taps.
Why do you need to know this?
in the rear area of the action you will be drilling through, no prob, use the taper tap, but in the front area of the action you will be drilling through the action but immediately into the barrel. You do not want to drill through into the barrel chamber!
So I suggest for this app, get you a plug tap (or two) and a couple of bottom taps. (more than one tap- they break and or can chip...)
Enjoy,
TresMon <--- Machinist