Resizing Bushing Size Question

[texas270]

Hoping to benifit from the expertise on the board. I have been trying two different bushing sizes in my Forster resing shoulder bump die, both of which seem to work "OK".

Can someone offer their thoughts as to the Pros and Cons of using the larger vs the smaller busing? Things like Bullet Runout, Velocity, Pressure, and Accurancy? thank much in advance!

 

[Mikecr]

If you partially NS your only going to produce ~2thou of springback tension(bullet grip) which is enough, and additional downward sizing would just be wasted.
More tension can be produced with FL/partial NS only as long as the sizing length is beyond bullet bearing seated.

I don't like FL neck sizing, and would not do this.
Whether you want very high tension, or very light, depends on the cartridge and it's need of pressures to perform. Seating w/resp to lands can come into play as well.
For example; If your expecting grouping in the 1s-low2s with a 30br, then you'll need to jack the pressures way up to burn the powder from a short barrel capable of this. Probably try it Jammed, but if best accuracy ends up off the lands, then it's gonna lead you to higher neck tension to get your pressures back(while not jammed).

Many shooters assume that high neck tension is beneficial. But this is usually not true.
Most of us aren't shooting jacked up underbore cartridges.
Lighter tension, means lower tension variance, and bullet jamming is a far bigger adjustment to load than neck tension anyway.

Just a matter of what it takes to get a load your barrel/cartridge likes.

 

[texas270]

Thank you Mikecr! this is some great feedback for me.

I think what you are saying is that there is not a standard rule of thumb, so try both(?).

I am loading 270 win with .301 and .302 bushings, only partial neck sizing and have been .002 to .004 off the lands.

Also, am embarrassed to say that I don't know what is meant by "grouping in 1's to low 2's with a Br"?

I am shooting a pretty hot hunting load and want to stay well below .5 MOA on the bench and below .6 MOA in the field. The rifle has done this consistently with a lighter lighter bullet (moving from a 130 gr to a 140 gr accubond).

thanks for any further wisdom!

 

[Mikecr]

grouping in 1's to low 2's

I'm meaning < .3 inches per hundred yards

 

[Bart B]

For box magazine bolt guns, a bushing 2 thousandths smaller than a loaded round's neck diameter is typically enough. Sometimes a bushing only 1 thousandths smaller works, or maybe one 3 thousandths smaller. Depends on the case neck brass thickness and metalurgy qualities. And heavier recoiling rifles need a tighter grip on bullets to keep them from seating back from impacting the front of the box magazine. It might take some testing to find out what bushing diameter is best; lighter grip is better for accuracy. Use what works best for your application.

 

[texas270]

Thanks again to both of you for the feedback!

Follow up question.....

I did a pretty extensive ladder test to come up with the best powder load using the smaller bushing. in going to a bushing which is .001 larger (hopefully less variance in tension and better accuracy) am I likely to need to redo the ladder test and change the powder load?

 

[Bart B]

am I likely to need to redo the ladder test and change the powder load?

Maybe. Depends on how reliable the data is from the ladder tests. I'd shoot at least 3 shots for each load doing a ladder test, otherwise they may not accurately represent where they're centered at.