Accurate T.I.R. seating

[Reg]

Checking with a RCBS TIR gage I have noticed that some some cast heads will sometimes run out as much as .005 even with great care in seating. Normally I set these aside and try to shoot groups with those showing little to no run out and save the "bad" stuff for chronographing, sighting in, plinking and other non critical shooting.
This TIR condition seems to be almost a thing of luck as even by doing what I think everything is right, it still doesn't seem to be totally controllable.
The dies used are RCBS and all case mouths are carefully chamfered with a 20 degree chamfer but once that head/case combination goes up into the seating die the dice seem to roll.
Are all seating dies created equal ?
Would a straight line type seater be worth while?
What are some of the tricks you have learned to keep things true?

:???::???::???:

[btroj]

Try a different seater or sizer.

First off, see of the neck of a fired case is straight. What happens when it is sized? What about after expanding for a cast bullet? What about after seating a bullet?

You need to see where the issue is occurring.

I find that using a rubber o-ring under the lock ring on dies helps, the die can float a bit to keep centered.

I had this problem when I started shooting NRA high power. My ammo wasn't straight and it hurt my scores. I changed dies and it made a huge difference.

[Scharfschuetze]

I'm not sure that .005" run out is going to matter too much. For my long range (600 to 1,000 yard) jacketed bullet loads for NM and long range competion, I was satisfied with .004" and less run out and when I did my part they stayed in the X and 10 rings easily. I did some testing with bullets with more run out and while there was an increase in group size, they often stayed sub MOA out of my match rifles and in the M-14NM rifle and M1A it just didn't seem to matter.

One can mark the bullet at it's highest point on the run out gauge and then chamber it (and others with similar run out) with the marked point at 12:00 O'clock and still enjoy good groups and accuracy. I often did this with my culls when the run out was excessive and damned if they didn't shoot pretty well that way. They made/make great practice rounds or rock shooting rounds.

Mark 'em with the run out point and how much run out there is with a Sharpie pen and give 'em a test against more uniform bullets and see what the difference is.

I might add that some of the army M118 ammo and even the superlative M852 and Federal Match 7.62mm issue ammo that I shot routinely in the M-21 and M-24 sniper systems and M-14 NM competition rifles was often .006 to .008 out of round and they still gave me good performance in the field in all conditions or on the competition range on perfect days.

Your die may actually not be the culprit here as I've had good Redding and RCBS straight line seating match dies produce bullets with at least .006" run out. Your neck uniformity may be partially responsible here. My long range cases were all fire formed when shooting the 200 yard stages of the NM course and then outside neck turned until they were all uniform in thickness throughout their entire diameter for the long range stuff. That often made the difference in small numbers and big numbers when checking the bullet run out.

[nhrifle]

I'm not as fussy about runout now as I used to be. At one point I made a runout gauge using bearings and a dial indicator, and also a tool to eliminate the runout. The second tool was a base with four bearings for the case to ride on and one to apply downward force to the case. A final bearing was lowered onto the bullet (jacketed at that time) a little at a time by a screw adjuster until the runout was eliminated. Something to think about if you think it might make a difference, and it doesn't take much more than a few things from a hardware store and some scrap metal to construct.

It's possible your dies could be seating the boolits inconsistently, and depending on how long the boolits are, that they are bending while still hot after dropping from the mould.

[Reg]

Some very , very good ideas coming out here. Keep em coming !!

[runfiverun]

ever measure from the bottom of your chamber to the centerline of your barrel?
.005 run-out doesn't seem like all that much anymore.

[Reg]

I think it all matters as to what you feel you need to do to get to the accuracy level you want.
I have played with this runout thing long enough to know that for me at least, it does make a difference. With some runouts running in the plus .003 / .004 range I never can seem to get the groups down where I think they need to be, the higher the runout , the worse things get.
Not every load is a accurate load but have noticed the ones that really tend to impress are the ones that among everything else also have a very low runout.
Some good ideas have been presented here and I will be checking them out.

[Jim Flinchbaugh]

Are you SURE its in the seating? I had an issue with nose bending during sizing and gas check seating.
Nose first sizing fixed that one
Ever look at the butt end of a RCBS sizer die /expander plug? they are NEVER concentric- always wonder how they made good ammo
then you read R5R's comment above and . . . does it really matter?

[44man]

It CAN matter! Two things are the chief culprits when loading. Many size dies size the necks down too much for a bottle neck case and pulling the expander out even with lube can bend the shoulders.
Next is brass thickness on the neck that varies.
Checking brass fired in my 30-30 was showing .010" to .012" run out on the brass, let alone out on a boolit. Cast is hard to measure exact, nature of cast with parting lines, etc. Most cast are not perfectly round either.
I neck turned just enough to make necks even and fired cases now drop from the gun at 0 to .002" run out.
Working with many calibers over the years, all kinds of seat dies, I never found bullet seating to be a big problem, the case was bent at the shoulders from what I explained.
The worst are Weatherby cases with rounded shoulders, the expander can bend them fast. I would send fired cases and the die to Redding and have the necks lapped for minimum sizing. That cured it and the Mark V's all turned into 1/2 min rifles.
Today we have the Redding collar dies, no expander needed.
Sizing alone never was a problem, it was drawing out the expander.
Remove the expander and size a case, it will be as straight as neck thickness variations allow.