Hey Nat,
I am in the process of building one myself for 140-160gr bullets. It is currently at my gunsmith being assembled. Here are my build specs.
Surgeon SA Repeater
Kreiger 1:9.5 #5 SS 24'
Badger M5 & AI 5 round mag, 2.88COAL max
McMillan A3
Jewel HVR
Dave Kiff reamer .317nk, .090fb, 1 degree 30 leade
What I can tell you without shooting it is that my extensive research indicates that a 1:9.5 should shoot 140's to 160's hunting bullets,140-160 Accubonds, and will shoot the 162gr A-max for target). If I was building one to shoot 120-140gr bullets I would go with a 1:10. What I can also say is that my Win brass loaded to 2.85 COAL fit in the AI mag,I only get 4 not 5), but
do not feed properly without modification. A very simple bending of the mag feed lips was all it took to achieve perfect and reliable feeding from the mag.
My virgin loaded Win brass necks measured .313 to .315. I brought them all to .313 loaded which cleaned up about 80-90% of each neck. A few, maybe 20 per 100 allowed for a full 100% clean up. This gives me .002 per side of neck/chamber clearance which is ideal for my intended application. It has been said by a few respected builders/shooters that too tight tolerances in neck/chamber create accuracy problems. I wouldn't go tighter than .0015 per side.
In terms of load development you'll need faster powders like RL15 & N150 with the lighter bullets. With bullets under 140grs you will have no trouble filling the cases with powder and staying under the 2.80 mag length. RL15, Noslers accuracy powder for the 284win with 120-140gr bullets only fills the case to 77% capacity with the 140's.
Here is an
absolute must read for people building a light bullet 284win:
Click Here.
Hope this helps. Good luck and have fun.
Keep us posted.
Kyle
