How to choose a bushing size?

Elkeater

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Ive always used a full length sizing die set to size just the neck but I’m looking at bushing dies for my .300 win mag and was wondering where to start. How do I choose the right bushing size? What’s the advantage over a full length size die?
 

bob4

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I've use Forsters Bushing bump neck dies. What I do is measure the outside neck furthest from the shoulder of a loaded round and choose a bushing .002 smaller than that measurement for .002 tension. The advantage is a bit more neck tension consistency and controlling tension. This is all assuming your necks are the same thickness. The better quality the brass the better this is without getting into neck turning.
 

AZShooter

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Measure OD of loaded round at neck. Subtract .003 and .002" from that value for the two bushings that are usually used. Some shooters of smaller cartridges may even try .001".

The issue in using bushings could be variable neck tension. Depends on how uniform the wall thicknesses of the necks. Norma, Lapua and RWS will have the most uniform neck wall thicknesses. Unfortunately Lapua doesn't make a 300 win mag or any belted case to my knowledge. The accuracy crowd that shoots BR use bushings that are used in conjunction with a custom reamer for a smaller neck diameter in the chamber and some neck turning for a much more precise system. Then the neck tensions are very similar. As near to identical neck tension is critical for the kind of accuracy the BR shooters desire. The advantage is longer brass life, less annealing due to less working of the necks with minimum expansion and resizing. There is another factor to consider: with a high recoiling magnum if the neck tension is too low the bullet would most likely move under recoil while sitting in the magazine box waiting for its turn. To test shoot three or four times with one cartridge staying in the mag box and measure that round to see if there is bullet movement. Another advantage in using bushings: during load development the bushing system can be useful for pulling loads that don't work and quickly resizing the necks with the bushing, no lube is necessary and primers can stay in the cartridge.

While it could work for hunting the sole use of a bushing die (assuming neck tension is same with good brass) not sizing the shoulders and body might make for a snug fit, counterproductive for fast cycling of bolt.

In theory using a standard FL die with a sizer ball, you could produce some neck runout. You are pretty much stuck with the neck tension the die produces. Typical tension for a 300 win mag would be .003" difference between sized and loaded round's neck. On the other hand you can get fairly consistent neck tension piece to piece even when the neck walls vary some in thickness due to the fact the die will drastically undersize the necks then the sizer ball will open the INSIDE of the neck to the proper dimension. It is going to work the brass more especially with the "sloppy" SAMMI neck chamber dimension.

IMO unless you use turned necks and a fitted custom chamber you will spend more money and may not see any improvement in accuracy.
 

L.Sherm

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As stated above bushing dies work the neck less if your using the correct bushing but the only way to control neck tension with a bushing die is to remove the expander mandrel. If using the mandrel you undersize by .002 from a loaded round that way when your mandrel comes back through the neck on the up stroke it sets your inside dia. of your neck that controls tension.
Some remove mandrel and only use the bushing to set neck dia. but if you dont turn necks the irregularity pushes to the inside.
Whiddens have a great explanation on there site about how to control neck tension and bushing vs non bushing which they state non bushing " typically" have better run out on your brass. I think floating carbide expander, annealing and lube with proper setup with a bushing die you can achieve good run out on your cases
 

bob4

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As stated above bushing dies work the neck less if your using the correct bushing but the only way to control neck tension with a bushing die is to remove the expander mandrel.
My bushing dies, to the best of my knowledge, don't have an expander. Bushing does all the neck sizing. Been my understanding to remove expander from FL dies. Correct me if I'm wrong.
 

L.Sherm

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Remove the expander from FL bushing or non bushing? Removing the expander from a non bushing would probably undersize the neck a lot unless it is honed for a specific size to the brass neck thickness.
 

dok7mm

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I have had excellent results using bushings that reduce neck I.D. by .003". Then, setting neck tension with a .002" under caliber mandrel, not the expander ball.

I turn necks on all my tight neck rifles, but this method will work well with unturned necks in factory chambers, as it pushes irregularities to outside of necks. Mandrel dies are available from K&M, Sinclair and others. Kenny Porter makes a great die that uses pin gauges.
 

Thundercat

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I have had excellent results using bushings that reduce neck I.D. by .003". Then, setting neck tension with a .002" under caliber mandrel, not the expander ball.

I turn necks on all my tight neck rifles, but this method will work well with unturned necks in factory chambers, as it pushes irregularities to outside of necks. Mandrel dies are available from K&M, Sinclair and others. Kenny Porter makes a great die that uses pin gauges.
 

Thundercat

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Thanks for info. I’m starting to use the Forster bushing die set.
This is a good place to start.
 

bigedp51

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My bushing dies, to the best of my knowledge, don't have an expander. Bushing does all the neck sizing. Been my understanding to remove expander from FL dies. Correct me if I'm wrong.
Redding recommends if the neck thickness varies .002 or more to size the necks .004 smaller than a loaded round and use the expander included with their dies.

The Forster bushing bump dies do not have a expander so you either neck turn your brass or use a expander die.

Bushing dies work best with custom tight neck chambers and neck turned brass.

And when reducing the neck diameter .004 or more with a bushing die it can induce neck runout. And why Redding recommends reducing the neck diameter in two steps when reducing neck diameter .004 or more.

And at the Whidden custom die website they tell you they get the most concentric cases with non-bushing full length dies.
 

dok7mm

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I'll jump in. Brass that's the same thickness around neck ( neck turned) will correlate the outside bushing size used to your inside neck diameter.

Necks that are thicker by .002" or .0015 on one side will not give same inside diameter (neck tension) as turned necks. Variation in neck thickness=variation in neck tension with bushings. A mandrel, run after sizing in a bushing die, will expand the neck thickness variation to the outside, leaving more consistent tension on the bullet. So, evenly turned necks react to a bushing die with more even tension.
 

L.Sherm

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I'll jump in. Brass that's the same thickness around neck ( neck turned) will correlate the outside bushing size used to your inside neck diameter.

Necks that are thicker by .002" or .0015 on one side will not give same inside diameter (neck tension) as turned necks. Variation in neck thickness=variation in neck tension with bushings. A mandrel, run after sizing in a bushing die, will expand the neck thickness variation to the outside, leaving more consistent tension on the bullet. So, evenly turned necks react to a bushing die with more even tension.
I agree with this, i just don't see were bushing dies work best just in tight neck chambers or turned necks. some guys dont like to turn necks so if you don't then i believe you have to use a mandrel to push the irregularities to the outside. If you turn necks the its o.k to just use the bushing. The tight neck thing is not as popular as it once was.
 

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