I need to pick up some new bits before i start building

Instead of buying a assortment, I wanna just get the sizes needed for completeing recievers?

Thanks in advance...

For gas blocks and front sight blocks :

Goal : drill to .117 and press in a .118" standard pin for a .001" press fit, or drill to .118" and press in a group 2 .119" oversize pin. (Arsenal or AAOK has the oversize pins).
Drills used : #32 (piloting) and then a #31 shaved down a hair in diameter for the final reaming.
Alternate : order metric drills in sizes 2.95 mm and 2.90 mm to set up to press in the (3mm) .118" pins.
For receiver rivets, buy # 18 through # 23 bits.
This will also cover the bits needed for the rear sight pins.

A  #8,#9 and a #10 bit can help if you need to drill reciever trigger pin holes, and a letter "I" bit is needed also. The "I" bit is used for standard trunnion pins, and "J" for oversized.

#32
#31
#23
#22
#21
#20
#19
#18
#10
#9
#8
I
J

13 bits total.
The #1 to #60 sets are really common.
There are some good suppliers also that can handle the individual bit orders.
Remember that all dowel pins are designed for a press fit, and that a drill of a specific size will always drill a slightly larger hole than planned.
Try for a .005 " press fit whenever possible.

I found a company that will sell individual reamers in any of the smaller sizes (such as .117"). I'll be making an investment after the holidays when they reopen.
For bits- check out DrillBitCity.com.

Not really a machinist. Aircraft mechanic for about 20 yrs, now a QC Inspector for small (business) jet mods and repairs.

Would anyone find it advantageous to use a centercutting end mill on a trunion cross pin where the barrel has never been cut for the pin? I imagine drill alone would have a tendency to walk a bit.

Good thought Antares! I cannot imagine how anyone could expect to get a decent hole (half hole) thru the top of a barrel with a bit alone and not cut into the trunion.
                                   Pete