Case and Loaded Round Runout question

[dlebeck]

Using a Sinclair concentricity gauge, what should my empty cases and loaded rounds have for acceptable runout???

Douglas

 

[Bart B]

Different case/cartridge lengths will have different amounts of runout for the same angle of neck/bullet axis relative to the body axis. A 6mm PPC will have about the same angles when measured near the bullet tip with a .001-inch runout as a .300 Win. Mag. having .002-inch runout measured the same place. Neck runouts measured at the case mouth will have numbers about half that measured at the bullet tip when the case shoulder-body junction is the reference. Which means shorter cartridges need smaller runout numbers than longer ones.

It's been my experience that .300 Win. Mag. size cartridges will shoot very accurate with no more than .003-inch bullet tip runout providing bullets are seated to touch the lands. If the bullets jump a bit into the lands, .002-inch bullet tip runout is about max.

If you mark sized case necks' runout high point then seat bullets in them, the bullets' high point will align at or near the neck's high point. Which means you gotta have pretty straight sized case necks if you want straight seated bullets.

 

[dlebeck]

So I guess I am not clear on how to measure runout? I am currently measuring case runout about midway up the neck on the un-fired case. On my once fired 300win mag brass I am getting about .007 runout. I thought this was very high? My loaded rounds I am measuring about midway on the bullet measuring from the edge of the case neck to the bullet tip and getting roughly the same result. /ubbthreads/images/graemlins/confused.gif

 

[älg]

You should be able to reduce that RO. Are you using a FL or neck sizer die??

Try adjusting your die with slight turns, resizing a case every time and cheking RO, you will find a spot where the RO is considerably reduced.

Depriming first with another die and leaving the expander a little loose also works some times.

 

[dlebeck]

Currently I am using a new set of Redding dies. The neck die is a type S that uses the bushing for neck size only. I have not run any of the subject brass through a body or FL size die. Using the Redding seater die that came with the set. Rock Chucker press that I have had for more years then I can remember. No problem with RO on other cals to date.

 

[royinidaho]

You didn't mention the Rifle make/model or cartridge....

Sounds to me like the cases may be out of round going into the neck sizer???

Any indications, by looking at the case, or measuring 'roundness' along the body length.

How about the 'ring' in front of the case head at the back end of the chamber (if its not belted)? Is it uniform?

Had a Swift like that one time, the chamber ended up being the problem. I marked the high side of each case and aligned it correctly for each shot. /ubbthreads/images/graemlins/frown.gif

 

[Bart B]

[ QUOTE ]
So I guess I am not clear on how to measure runout?

[/ QUOTE ]With the case supported on its body with one set of supports just behind the shoulder and the other 1/8th inch in front of the extractor groove, put the dial indicator about 1/8th inch back from the bullet's tip for bullet runout. Measure neck runout with the dial indicator touching the neck about 1/16th inch back from the case mouth.

If you want to see some interesting stuff, set up the tool so the dial indicator can measure runout on the body just behind the shoulder or 1/8th inch in front of the extractor groove. Most folks fall out of their socks when they see how much out of round cases are at these places.

If you take 10 new cases, load them, then orient each one in the chamber with the headstamp in the normal readable (upright) position, shoot them, then measure them for out of round points on the body. They'll all have a different high point relative to the headstamp which means each one expanded all the way to the chamber body walls but shrank back unevenly. Why? Well, the body wall thickness isn't the same all the way around so the thicker part won't spring back the same amount as the thinner part.

And if you can measure the chamber for out of round, too, then compare fired case measurements to the chamber it helps folks understand why there is no such thing as a perfect fit of case to chamber.

 

[Tim Behle]

One of the first things I found several years ago, when I first became aware of run out. Was to take a Slow, smooth and steady stroke on the ram when sizing.

I was amazed at how much I could reduce the run out in my cases, just by taking my time and working slower on the press.

 

[dlebeck]

Now I am getting somewhere. Thanks for all the replys. For the record I am shooting a Savage 110Tech in 300win mag. gun is stock and I bought it used. Useing brand new redding dies with an S bushing neck die. RCBS rockchucker press and redding shell holder. The gauge is by Sinclairs. Brass is Frontier and bullet is the 180 serria.