Bullet run out

[Davy]

I was reloading for my 7mm SAUM wildcat again last weekend and despite every trick I know I still get excessive and erratic bullet run out, typically anything from .002" to .008" measured at the point the bullet would pick up the lands.

 

The brass is Norma, I have neck sized to .012" for a .312 neck so I should have a couple of thou clearance which allows for any potential fouling when shooting longer strings.

 

I use Forster dies - A bushing bump die with a .306" bushing so neck tension is quite low and an ultra micrometer seater.

 

(For me these are tried and tested dies and as a comparison I use the same make and process for my wife's 22-6,5x47 and get bullet runout of between .000" and .0005" sometimes moving to .001" - so an accurate build in that respect.)

 

The brass is either once or twice fired, I do not tumble, instead choosing to hand clean the outside of the necks and the inside of the necks are cleaned with a .30 bronze brush in a power screwdriver pushed in and out once in a smooth pass, so they are clean.

 

Press is good and solid and dies are locked down. I use a very light wipe of imperial sizing wax and neck size in one pass.

 

What am I missing or doing wrong?

[taylor]

whats the run out of a fired case davy ,with custom dies and a straight chamber i get next to zero runout ,i know factory dies produce quite a bit of run out ,need to check if the run out is in the fired case or sizing operation or seating op

if its a bushing die let it float dont tighten down on bushing .and dont lock down the lock ring tight let that float .use a o ring under lock ring to tighten down ,same with all dies ,i use arbour press seater dies copyed to my chamber to eliminate runout

i use 2 thou size down from loaded round .

[Davy]

whats the run out of a fired case davy ,with custom dies and a straight chamber i get next to zero runout ,i know factory dies produce quite a bit of run out ,need to check if the run out is in the fired case or sizing operation or seating op

if its a bushing die let it float dont tighten down on bushing .and dont lock down the lock ring tight let that float .use a o ring under lock ring to tighten down ,same with all dies ,i use arbour press seater dies copyed to my chamber to eliminate runout

i use 2 thou size down from loaded round .

 

Thanks for the reply Taylor. Run out on a fired case is virtually nothing, certainly less than half a thou worst case. Once resized it moves to around .0015" and then once the bullet is seated it jumps all over the place. I will try the O ring trick. I already allow the bushing to float by a few thou, I have considered blending the lead into the base of the bushing so the case neck is sure to go in straight.

 

What i have not done yet is marked the fired cases, I will try that next time to see if I always get the neck run out in the same place with reference to the mark. The other thing I am tempted to do is drop the bushing size by .001"

[taylor]

it sounds like its the seating operation ,try floating that die and drop neck tension and also try polishing inside of neck with fine steel wool on a old bronze brush helps bullet go in easy if no luck but a new seater .also chamfer on inside and outside of neck then polish with steel wool

lets bushing go in straight with a wee bit lube on neck

good luck

[Davy]

Success! I re-polished the lead into the bushing, allowed a bit more float and most significantly locked the die down onto an O-Ring, the ring allows the die to wobble very slightly. Now I see case neck run out peaking at .001" and usually better than .0005" A huge improvement and a handy tip as well

 

Many thanks indeed.

[Laurie]

Another tip that often helps is to only half-seat the bullet, back the press handle off, and turn the cartridge through 180 degrees before completing the seating operation. This technique evolved during the days of crap brass and poor quality dies by today's standards, but usually still pays off even with top quality match dies.

[Davy]

Another tip that often helps is to only half-seat the bullet, back the press handle off, and turn the cartridge through 180 degrees before completing the seating operation. This technique evolved during the days of crap brass and poor quality dies by today's standards, but usually still pays off even with top quality match dies.

 

I have experimented with half and quarter turns and have to admit I am yet to see any significant improvement with good quality dies however I still look on it as best practice when building. I am still sitting at the bench marvelling at such low neck run out after the frustration of the last few loads, and all for 2p worth of O-Ring!

 

Now if only they did an O-Ring that worked on wind reading............

[taylor]

glad you got it sorted -

Grant