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Old December 1, 2020, 12:52 PM   #1
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Neck expansion question

I have a question to ask about proper neck expansion for cast bullets.

My rifle slugs at .3105" so the proper sized bullet should be .3125". If I hone out my bullet sizer to .3125, using the current expander of .3110" leaves a difference of .0015". What is the ideal difference between the resized cast bullet and the inside diameter of the resized neck of optimal accuracy? I don't think I can get away with the current .311 expander. A bullet sized at .311" using the Lee sizer die kit fits just right.
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Old December 1, 2020, 01:25 PM   #2
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A couple questions. First, I am not familiar with the Lee bullet sizer, but is it made of soft enough steel so as to be honed out? Second, I don't know what rifle you are talking about, but anywhere's from .001" to .002" is enough case neck tension unless you are using a rifle with a tube magazine. And lastly, just because you have a .311" expander does not mean that the case neck inside diameter will be .311". Actually, it will be slightly less due to brass spring back.

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Old December 1, 2020, 09:42 PM   #3
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I am not familiar with the Lee bullet sizer, but is it made of soft enough steel so as to be honed out?
Sizing dies are hardened. They can be honed larger because the grit in the honing material is harder than the hardened steel.
I machined a sizing die one time when I was under the impression that soft mild steel being harder than cast bullets, it would not need to be hardened. I was wrong and after a short time of using it to size .430 cast bullets, the bore of the die had become much larger than original. After that, I remade the .430 die using W-1 drill rod and hardened it after reaming the bore of the die. Using hardened W-1 did the trick...the die maintained its inside diameter for the many years I used it.
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Old December 1, 2020, 10:14 PM   #4
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BartB says the military armorers found 0.0015" to maximize accuracy with jacketed bullets in their 30 cal guns. Cast bullets typically get about 0.001" more because they are usually that much wider than jacketed bullets, but that doesn't mean they wouldn't like 0.0015" better. Unfortunately, this can be dependent on the gun and the load, so you are going to want to try it and see.
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Old December 1, 2020, 10:45 PM   #5
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Uncle Nick, thanks for answering another question I had for jacketed bullets. I was thinking of expanding case necks before seating 174gr FMJBT bullets before seating them. The only question is if I should anneal the necks and graphite the necks too.

I measured the RCBS expander plug diameter as .3105" compared the sized bullet through a Lee bullet sizing die as .31105" That's a difference of .001"

I have to correct an earlier typo. The slug I pushed through my T99 Arisaka was .31105". The bullet diameter should be +.001 or .31205". The inside diameter of the case neck goes back -.001 and I'm back to .31105" or an additional -.001 according to Uncle Nick which is .3105", which the current plug measures at. Using the jacketed variance might be better to avoid swaging, plus I'm using gas checks.. Hmm.. okay, thanks for letting me think this out.
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