most important factor affecting runout

[Deleted old_dood]

bullet seater, case prep, or sizing die? sometimes my methods give me outstanding runout and sometimes, not so much. 6mmbr, Forster bushing bump die using bushings .001" or .002" smaller than loaded bullet at the neck. seater is RCBS competition. I chamfer inside neck with Sinclair VLD chamfering tool.

 

[22BRGUY]

All of the above in my experience. I've also learned that chamfering alone still leaves an edge inside the case mouth that is sharp and can "catch" on the side of the bullet as its being seated. I use a green Scotchbrite pad and push the mouth of the case into it after chamfering and turn the case back and forth several times. I can actually feel the chamfered inside the mouth sharp edge smooth out. JMHO

 

[Martin52]

bullet seater, case prep, or sizing die? s

Assuming no fundamental problem in the brass itself, my experience is that the sizing die and case prep has the most influence on run out. I find a FLS die is the best to use in order to minimise run out. I remove the expander to avoid the neck being stressed and turn my case necks and generally this produces minimal run out. I have not been so succesful using neck sizing dies, run out has got up around 0.004. However, run out using a Lee Collet die has been on par with my FLS die, 0.001

 

[fdshuster]

old_dood: You did not mention "quality of the brass". Some new factory brass is excellent (Lapua), some is "good" (Winchester), and some is outright junk. I won't identify the junk because I know there are those who will defend it, but spinning the brass under the Sinclair concintricity runout gauge tells the truth.

I had a box of factory ammo (20 rounds given to me) that had loaded round runouts of .010" to .015", so bad that you could watch the front end of the cartridge jump up and down, radically, while spinning it under the dial indicator. I did not even shoot it, as my custom barrels are too good to be fed garbage.

 

[Deleted old_dood]

it's Lapua brass. I've got between 13-15 uses on my first 100 (down to 95 now) and I found that I've had to use my Redding body die a few times on them. It seemed like I needed to FL size more often so I bought another 100 cases and a Redding FL type S die but have only fired 20 of the new cases and have not reloaded any of the new ones yet. With regard to polishing after deburring/chamfering, I packed some 0000 steel wool into a socket and press the neck into it while spinning. I was mainly concerned whether the RCBS seater was the most likely cause of the runout (usually .004" on a bad one). I did drill out the stem on it in case the tip of the bullets were bottoming out inside.

thanks for the replies.
Al

 

[fdshuster]

Al: When using Lapua brass, (6BR, 220 Russian/6ppc, 308, 222, 223) I may get 2 out of a box of 20 that have loaded round runout of .004" maximum. Unlike the other 18 in my "sample" box they will not straighten out no matter how many firings. The 2 will be kept for first round foulers, short range only, informal not match use. If it's only a few of yours that have runout you're not comfortable with, then I believe it's nothing more than slight defects that were created when the brass was drawn.

If all 20 of my sample brass had excess runout then I would look at the dies, sizing methods, etc.

You might also check them for runout after each step in the reloading procedure to try & narrow it down to where the R/O is developing. After firing, after sizing, after bullet seating.