Selecting the correct neck bushing

[elwaine]

Hope ya'll don't think I'm nit-picking with this question, but I want to know how to determine the correct size when selecting a bushing for a neck re-sizing or full length re-sizing die.

The instructions that came with the dies say to measure the outside neck dimension of several factory cartridges and subtract .002" or .003" from that figure. Maybe .001" doesn't matter one way or the other, but my assumption is that the tighter the bullet is held in the case neck, the higher the pressure. If that's true, there should be a difference in performance.

Is there a simple rule of thumb, or do you have to work up a load using each bushing size and determine the results that way?

Thanks in advance - Larry

 

[Walkalong]

I assume you are talking about a bolt gun.

Tight neck tension helps get good start pressures and that usually leads to good ES & SD's, usually. You can get more consistent neck tension with light neck tension, but then you need to be able to load rounds that touch or are just into the lands to get your good start pressure.

They way they recommend does not always work out just right. Expect to have to buy more than one bushing. Do the math, give it your best guess, and go from there. Try it and see if you get the results you want as far as neck tension. BEFORE you chamber and fire a round you need to know you have enough neck clearence in your chamber. If it is stock, no worries. That is only a problem with tight necked match chambers or when you size brass down a caliber or two case forming brass which thickens the neck.

The carbide bushings are exspensive, but are the best, the Redding nitrided bushings are next, and the steel ones work fine, but need a good lube. I suggest Imperial Sizing Die Wax.

Bottom line is you will have to try each load with whichever bushing you use to see how it does on paper in the real world.

 

[USSR]

The instructions that came with the dies say to measure the outside neck dimension of several factory cartridges and subtract .002" or .003" from that figure. Maybe .001" doesn't matter one way or the other, but my assumption is that the tighter the bullet is held in the case neck, the higher the pressure. If that's true, there should be a difference in performance.

elwaine,

The instructions you have are outdated. Redding has changed their recommendation (and I concur). From their website:

TO DETERMINE BUSHING SIZE
The proper bushing size can be easily determined by measuring the outside neck diameter of your loaded cartridges with a precision micrometer. Then, simply subtract .001" from the cartridge that had the smallest average neck diameter. See "Tech Line & Tips" for complete explanation.

Also, pressure is more a factor of seating depth (as it relates to distance to throat) than neck tension, so select whatever amount of neck tension you and want and forget about it. I use .001" to .002" neck tension on boltguns, and .003" to .004" neck tension on autoloaders. As Walkalong stated, get the nitrided bushings and save yourself from having to lube your necks when neck sizing.

Don

 

[layusn1]

So, would it be safer to buy a few bushings, experiment with them all until you find the best one and then eBay the other ones? In the grand scheme of things buying and keeping a few different bushings shouldn't kill the wallet right? What about brass manufacturer case neck thickness variation...could it be significant enough to use different bushings with different brands?

 

[kelbro]

Yes, different brass manufacturers have varying neck thicknesses that will require different bushings to maintain the same neck tension. It may even vary between different lots of the same manufacturer's brass.

 

[elwaine]

Don, Walkalong,

Thanks for the info. Yes, I am talking about bolt guns. I have top of the line RCBS dies and use their titaniun nitride bushings (they do not require lube when neck sizing only). BTW, thanks for the previous advice re: the RCBS precision Mics. They arrived today... way cool!!!

Larry

 

[USSR]

So, would it be safer to buy a few bushings, experiment with them all until you find the best one and then eBay the other ones? In the grand scheme of things buying and keeping a few different bushings shouldn't kill the wallet right? What about brass manufacturer case neck thickness variation...could it be significant enough to use different bushings with different brands?

Yes, case neck thickness varies from brand to brand of brass, so you will find yourself using various sizes of bushings. In .30 caliber I have: .338", .336", .334", and .332". Winchester brass is the thinest brass, and you will need a .332" or even a .331" bushing for it.

Don

 

[layusn1]

Cool, thanks for the info.