Re: HELP - high bullet runout
I'm using a Co-Ax as well and found several causes for high runout unrelated to the press but not necessarily different for different calibers as the OP is seeing but thought I'd throw out some observations in case some might help.
BTW, the screws through the jaw hold-down plate should be finger tight only or the jaws can't move freely enough. You can tell if they're too tight if the jaw opening screw is getting chewed up. Had to replace the plate at one point along with the bearing plate under the jaws due to tightening the screws just a bit with a hex key.
Some things that worked and some that didn't in the order (mostly) of discovery (read: stumbling blindly about):
1) With Forster dies very carefully set the height of the expander ball using a pair of dial calipers rather than trying to sight through the hole in the side of the die - slight misadjustment caused large and variable runout.
2) Learned to tighten the stem lock ring only finger tight so it can float on the rubber washer - made a slight but noticeable improvement but didn't come close to fixing the problem. And the decapping pin kept smacking into the side of the flash holes of Lapua brass, no idea why.
3) Had the Forster FL and NK dies factory polished including the expander ball - reduced runout by more than half but still had more fliers than I thought there should've been.
4) A lot of the problem was brass build-up from inadequate lube on Lapua brass (and the reason the dies got sent to Forster in the first place) - learned how to properly use Imperial Die Wax, not as simple as it looked at first as the bottom of the case gets a lot of swaging and needs more lube than you'd think, well more than I thought it would anyway.
5) Forster strongly recommended chamfering prior to sizing. Dented necks made this impossible and I wasn't using a VLD cutter yet. Started using the Lee Collet die first to size the necks (after lots of work to polish the die collet) and then as an expander only to remove dents. Switched to the Sinclair expander mandrel die after the mandrel in the Lee die picked up too much brass even with Imperial Dry Lube on the necks. Learned to get the deburring and VLD chamfering done under power with Sinclair case holding chucks in a power screwdriver and sizing became much easier with much less brass build up on the expander ball. Runout variance tightened up noticeably.
6) Along the way started winding 0000 steel wool around a nylon brush (as someone already mentioned) and using it to polish under power the inside of the necks. Eventually reduced to just smoothing the internal neck surface after VLD chamfering, both prior to sizing and prior to bullet seating after trimming. Sizing force became noticeably more uniform. No significant effect on runout though.
7) Along the way switched to a Wilson trimmer. Whether it helped I couldn't say as it wasn't tested as a separate change in the operation sequence. The Lee trimmer used up to that point seemed OK but if having the case mouth square to the case body axis is important it won't do the trick.
8) Had a problem with the Forster seating die scuffing bullets so sent it in with the finishing reamer used to make the rifle and they made a seater with it that eliminated that problem, cost was like thirty five bucks. Runout didn't change much if any but bullets didn't get scarred up anymore.
9) Changed from VLD chamfer to a caliber diameter Wilson neck reamer prior to seating. Bullet can be set pretty much dead square and seated more uniformly, or at least it makes it a lot easier to get a inline start at seating since the bullet is held tightly by the neck when the case is set in the jaws. Runout didn't change much if any again although it may have tightened up, subjectively anyway. By this point I'd gone through several different ways of measuring 'runout' with a Forster Case Inspector and was convinced none of them provided any meaningful data.
10) Changed the way I was measuring runout while still using the Forster Case Inspector. Picked up a Besttest dial test indicator (+/-0.015"), some swivel clamps, and 1/4" drill rod. Removed the dial indicator from the Case Inspector and attached a short piece of drill rod with a swivel clamp and then attached the Besttest to it with another swivel clamp. Squared it up and set up the cases to indicate on the bullet bearing surface. Added a spacer to remove the spring loading on the case head and set it to ride the vee-block on the web with the bullet tip freely held at the other end so the axis was as visibly level as possible. The nose of the support arbor still has the tit from the cutoff tool and any pressure from the spring loaded base caused the bullet tip to ride off the cradle, disturbing measurements (took a long time to notice this). With almost no radial force applied by the dial test indicator it was possible to slowly spin the round and get a smooth indication of runout relative to the case head which had by this time been reduced to near zero for most rounds with some about half a mil to one and a half mil TIR. It wasn't possible before for me to measure this repeatably with the dial indicator setup but it seemed like it was pretty close to zero except for the number of unexplained fliers. The dial test indicator can be moved along the drill rod and the runout of the case at various points can be measured easily and is helpful in noting case runout can be higher than that on the bearing surface and is slightly dependent on the runout at the point on the case that rides in the vee-block.
FWIW, the dial indicator it came with ended up on a granite base comparator stand which works well with the Case Inspector base and pilot to measure neck thickness more repeatably than before, too.
One last note. I got annoyed at the brass build up from annealed necks on the expander ball on the Forster dies and switched to Redding bushing dies (FL and NK) with the carbide expander ball. The neck isn't overworked as much and the bushings can be changed for Lapua, Win, BH Match, etc. brass thickness which I couldn't do with a single set of honed Forster dies. Runout is still just as low as it was before and just as tight a distribution meaning, to me at least, the most important part of getting low runout appears to be case prep _prior_ to sizing. Kinda what the guys at Forster were trying to tell me to begin with... duh
Yeah, it's a serious pita the first time through but it gets easier although getting the necks sufficiently clean inside can get worse. Switched to bronze brushes for this step and it makes it go a lot faster - the case has to be chucked in the screwdriver anyway so a few swipes with a heavy duty bronze brush in a handle at the end of all the operations is all it takes now. When the brush starts being easier to push into the case mouth it gets replaced.
Spent a lot of time with Starrett small hole gages and a mic, clamped in a stand, checking neck ID before and after sizing, from the mouth to the shoulder and found that different brass puts tension on the bullet at different points and for different lengths of the neck and it depends on how many times it's been fired. But runout doesn't seem to change much if sizing prepped brass.
Probably forgetting some things, hope this is of some help. Oh yeah, no neck turning. All rifle chambers minimum SAAMI so all brass loads safely. Bearing surface of bullet matters most so neck ID runout matters most which is why I use an expander ball and don't depend on neck turning and bushings to keep the neck true. Redding reports the more the neck has to be worked in this way the worse the runout gets. Makes sense to me from what little I've seen so far. But I still can't outshoot the rifle(s) so it really don't matter all that much 'cept being fun.
