RUN OUT / ACCURACY

[Bill Norris]

For those that pay attention to run out on turned brass for tight-neck chambers what is the acceptable number on the concentricity gauge for considered top accuracy.

 

[Murray Brook]

For the non-competative bench shooting I do with my 6mm Br at 100-200 yards I find that anything .003 and under is good. Only when I get above this do I seem to notice an increase in group size. Normally shows itself, in my shooting, with a flyer. Now mine you my reloads are generally around .0015 run-out but I have tested with more run-out. My chamber is a no-turn .2725. I feel certain that at distance (500-1000 yrs) things would be different. JME

 

[Alex Wheeler]

Bill, the bullet is in the freebore with about .0005" clearance. The next tightest spot is probably the base of the neck or shoulder, about .001-.002" clearance, then the base, .0005-.001 clearance. Plot all that out, thats the max runout you can have once a round is chambered. At least on longer bullets it not something I have been able to shoot the difference on. I can see on a short bearing surface bullet with very little freebore how it could be more important but I dont know that for sure.

 

[mikecr]

Acceptable runout is anything less than chamber clearances for the loaded brass.
When TIR reaches a point of creating chambered pressure points, it can throw shots.

 

[Ray123]

I don't shoot rifle chambers requiring neck turning...but I always spot check runout when loading ammo...today most brass and dies do a good job with almost zero to .0015," on most. So I don't worry about it.. and there was a test where around .003" TIR shot as good as .001" TIR .I did skim neck turn all my 50 BMG brass, because of obvious reasons....when I check them most are .001" or less, a few will hit .002" with military brass and military bullets some of which are resized and slightly out of round. I have shot a .6" 5 shot group at 100 with non resized military APIT 620 gr bullets...not bad for a .510 dia military bullet.

 

[Ledd Slinger]

Good quality bullets in Lapua or ADG brass with necks turned on a high quality tool and using good dies usually always yields a TOTAL runout less than .001” for me. Many times it’s .0005” or less. But like Alex said, it’s gonna straighten itself out in the chamber pretty good anyhow. I usually check runout on fired cases once with each new barrel, and/or die sets, or if I swap bullets to ensure the seating die is seating them straight. If it’s good then I don’t check any of it again until the next barrel.

I’ve heard of competitors running .001” neck tension on bullets and using a long jam seating depth to let the lands sort out where it wants the bullets to be in the bore. Maybe a good idea so long as you are sure your lands is cut perfectly even and concentric with the bore and chamber. But if using that method, don’t chamber a round unless you know for sure you’re gonna pull the trigger on it!

 

[Bill Norris]

Thanks guys for your response. I was interested in this due to me having a 30BR with a .330 turn neck chamber in which I turn the necks down to @.098 to give me .327 to .3275 loaded round diameter. I am finding brass neck run out to be @ .0005 to .001 on the concentricity gauge and neck wall thickness measured with a micrometer to have a variance of about .0005 max. I do not compete except with myself but just wanted to see if my brass prep was anywhere close to the level of BR.

 

[Sandstorm]

Bill if it shoots well for you, your doin fine....Let the target tell you.

 

[bobm]

Bill if it shoots well for you, your doin fine....Let the target tell you.

Bill's targets talk to him all the time. He's got brass prep nailed.

 

[Bill Norris]

Bill's targets talk to him all the time. He's got brass prep nailed.

Thank you for the kind comments Sir.

 

[shoot4fun]

Anyone ever check the accuracy of their tool for measuring runout?
Just running that out there.

Thanks guys for your response. I was interested in this due to me having a 30BR with a .330 turn neck chamber in which I turn the necks down to @.098 to give me .327 to .3275 loaded round diameter. I am finding brass neck run out to be @ .0005 to .001 on the concentricity gauge and neck wall thickness measured with a micrometer to have a variance of about .0005 max. I do not compete except with myself but just wanted to see if my brass prep was anywhere close to the level of BR.

But seriously....
Maybe I am the lost boy here but several replies seem to be replying to total runout of a finished round?
It would seem to me that you are not to the point of having a completed round on the concentricity gauge with these numbers.
If I am correct my only question is "will you turn my brass for me?" because those are da$n tight numbers sir.

 

[watercam]

One of the fastest ways to eliminate runout it to seat your bullet half-way, then turn the case 180º and finish seating. For me the difference is 0.003" w/o turning, 0.000-0.001"
total runout.

 

[Bill Norris]

One of the fastest ways to eliminate runout it to seat your bullet half-way, then turn the case 180º and finish seating. For me the difference is 0.003" w/o turning, 0.000-0.001"
total runout.

Absolutely. My TIR on the bullet range is .0005 to .001 with occasional .0015. Maybe 1 out of 20 rds. or so.

 

[Bill Norris]

Anyone ever check the accuracy of their tool for measuring runout?
Just running that out there.

But seriously....
Maybe I am the lost boy here but several replies seem to be replying to total runout of a finished round?
It would seem to me that you are not to the point of having a completed round on the concentricity gauge with these numbers.
If I am correct my only question is "will you turn my brass for me?" because those are da$n tight numbers sir.

LOL. I will tell you what I use and my method.

I use a Forster hand held turner with a Hammerhead cordless screwdriver (variable speed) and the Sinclair shell holder-driver. See pic below.

I divide the amount I need to remove into half to reduce the amount removed at one pass and run the screwdriver slowly and feed the case neck onto the mandrel slowly as well.

Once I have completed the final feed I allow the case to run back and forth on the mandrel (slowly) until I see no tiny shavings being removed. I believe this step helps keep the numbers lower.

I then polish the necks with # 0000 steel wool to give a smooth and shiny surface.