A lot has been written about NECK TURNING, but very little about NECK REAMING. IT seems to me reaming makes more sense. Variation in case wall thickness cause the case to stretch unevenly resulting in a bowing of the case body. This results in the axis of the neck being unaligned with the body. So when the round is chambered the bullet will not be “looking" straight down the bore. This cannot add anything to accuracy. At least that is my take on the subject.
I took 50 once fired 30-06 GI cases and preped them in the usual manner. THen I used my Wilson case trimmer to neck ream 25 of them. Jacketed bullets were then seated in all the cases and the bullet runout measured using a NECO concentricity gage and got the following results. Runnout (RO) was measured on the bullet just in front of the neck.
Necks Reamed
0 =< RO <= 0.002: 20 cases
0=< R) ,= 0.004: 5 cases
Necks not Reamed
0 =< RO =< 0.002: 10 cases
0.002 < RO <= 0.004: 14 cases
0.004 < RO <= 0.005: 1 case
NOTE: “<” means less than
“>” means greater than
“=” means equal to
THese results show than reaming produces necks concentric with the axis of the case. I don't know if this will result in better accuracy. Only time will tell. What do you gents have to say about this?
Jim/cityboy