excessive bullet runout on new 7-08 AI

[jmbn]

I could use some advice on a problem with a new chambering. A friend just gave me a new stainless take-off barrel in 7-08 from a 700 CDL, and I had a gunsmith rechamber it to 7-08 AI and I put it on a proven 700 short action that I've had for about 30 years.. I had some new Lapua brass in 308 and using some new Hornady dies I necked down the necks so that it was a firm fit in the new chamber and fireformed the box of loads by taking it along on a sage rat hunt.

I bought a new Redding FL die in 7-08 Imp. and loaded enough rounds for several groups using both Nosler BT's and Hornady SST's, both of which I had on hand. I used the Hornady seater, which is a "Dumore" die which should work for everything from 7-08 to the 7mm belted mags, maybe even bigger. The groups ranged from 1.25 to about 2", which is pretty disgusting. On my return I ran the remaining loads thru a runout indicator and there was as much as .012 runout on the bullets. The runout on the necks of the fired cases was almost nothing. I had not turned down the necks of the brass yet, but obviously checked to be sure that there was clearance for the loaded necks.

Any ideas about what's causing this runout? I did not think to check the runout on the virgin brass that I loaded for fireforming, and it's too late now. I'm thinking it might be the seating die. Most of my life I've used RCBS dies and have not had a problem other than many of the sizing dies being tight, which I correct with a drill press and valve grinding compound. Have any of you used the Hornady dies with the universal (for caliber) seaters? Another possibility, it seems to me, is that the expander nipple might be pulling the necks off-center.

I'm a deer hunter, not a benchrest shooter, and if this rifle will shoot ¾" groups I'll be happy, and if it shoots ½" groups I'll be delighted. Since this runout is much more than any of my other rifles I think I should look there first before condemning the barrel.

Thanks for any input.

 

[Guest]

I expect your runout problem is from the expander button pulling the casenecks off center.You'll need to tune up the dies.Loosen the de-capping rod,insert a case in your shellholder,run it up and tighten the de-capping rod down.Check a couple cases you size.if they still show much runout,turn the spindle in about 32nd increments until your cases come out less than .004 or less runout. Good luck

 

[Buffalobob]

While you are checking the adjustment of the decapping pin, check to make sure the decapping rod itself is not bent. That will really give you grief. I just got a new one for a die because I bottomed out the old one and the new came "pre-bent" (and naturally I broke the new one trying to straighten it without heat).

 

[kraky2]

Here's a system that works for me...I keep a copy and post it when runnout comes up.....

My $.02 worth---ALL dies with expander balls need tuning. Think about it...a piece of typing paper is .003" thick--what are the odds that the expander is not PERFECTLY centered in a die??? Pretty good I'd say. Pull the expander stem out of the die (and now is a good time to clean the inside of the die). Run about 5 brass into the die and see if they come out concentric. If they do (and usually they will) you now have to try and get that stem centered on re-assembly. A great way that helps is to put a piece of very concentric brass up into the die to hold the stem in place as you tighten it down. Sometimes this takes 2 people unless you have 3 or 4 hands. AFter reassembly try sizing some brass and check runnout. If not good then do very small turns of the expander stem--probably 1/32 of a turn at a time. Resize some brass and repeat the small turns. At some point I can almost guarantee that you will get GREAT RUNNOUT CONSISTANTLY. (Somehow, someway the expander spindle will hit almost perfect centering in the die body) I have many dies that consistantly make less than .002" runnout after sizing with most of the brass at .001" and less. I own, hornady, redding, forester, rcbs, and lee dies. ALL OF THEM HAVE BEEN TUNED and most make fantastic ammo and all make good ammo!! I have never ever got a set of dies from any factory that made as good of ammo as those that I have done this simple work with.

 

[jmbn]

I'll play with the expander this weekend. A question comes to mind; I've always set the decapping pin to cleanly remove the primer when I resize, and it seems like the expander ball doesn't make contact with the neck until the case is halfway removed from the die. If this is correct, doesn't the case just find it's own position and index off the expander ball with little or no contact with the rest of the die? I must be missing something. Do you decap the case with an independant decapper, like the ones I have to decap military brass? Maybe this would allow you to set the ball so that it goes thru the neck while the case is still well into the die?

 

[kraky2]

I know what you are thinking that maybe the case should move a little since it isn't held by the die but it doesn't seem to work that way. I've read where people take the expander ball out of their die, do the decap and resize then put it back in and just run the case neck over the expander ball but that seems like alot of monkeying around. If you can hit the "sweetspot" with that spindle your problems are over. OR take a look at the post below about the guy with necktension questions. You may want to get a universal decapper and a lyman M die for about $12 ea and try the system described there.