GBCAPT
04-11-2011, 07:27 PM
I bought a Lyman - think it was called O-mag - press years ago that never produced really accurate reloads. Then I was gifted an RCBS Rockchucker that produced excellent reloads using the same components and loads in the same rifles.
So the Lyman went to a back shelf and has remained there until recently. I re-discovered it over the winter, and for lack of other distractions, decided to try to figure out why it seemed to produce inferior reloads.
I took two pieces of brass from the same group, resized them in the same die with the same shellholder and seated bullets from the same box. Then checked them out on an RCBS comparator. The O-mag sized/seated round had way, way more runout that the Rockchucker sized/seated round, so it must be press related.
Then I started closely examining the ram/shellholder relationship to the bottom of the sizing die.
The Rockchucker is in perfect alignment with the top on the shellholder contacting the bottom of the sizing die at the same time.
HOWEVER, THE RAM/SHELLHOLDER OF THE O-MAG ONLY CONTACTS THE FRONT LIP OF THE SIZING DIE WITH A SLIGHT, BUT VISIBLE GAP AT THE REAR EDGE! So, case rims must be out of perpendicular alignment to the bore of the sizing die, causing the excessive radial runout and diminshed accuracy.
Anyone know of a cure or is the O-mag destined for the scrap recycler?
So the Lyman went to a back shelf and has remained there until recently. I re-discovered it over the winter, and for lack of other distractions, decided to try to figure out why it seemed to produce inferior reloads.
I took two pieces of brass from the same group, resized them in the same die with the same shellholder and seated bullets from the same box. Then checked them out on an RCBS comparator. The O-mag sized/seated round had way, way more runout that the Rockchucker sized/seated round, so it must be press related.
Then I started closely examining the ram/shellholder relationship to the bottom of the sizing die.
The Rockchucker is in perfect alignment with the top on the shellholder contacting the bottom of the sizing die at the same time.
HOWEVER, THE RAM/SHELLHOLDER OF THE O-MAG ONLY CONTACTS THE FRONT LIP OF THE SIZING DIE WITH A SLIGHT, BUT VISIBLE GAP AT THE REAR EDGE! So, case rims must be out of perpendicular alignment to the bore of the sizing die, causing the excessive radial runout and diminshed accuracy.
Anyone know of a cure or is the O-mag destined for the scrap recycler?