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Old July 25, 2010, 12:25 PM   #1
Spent Casing
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.30 Throat size?

Am I missing something here? Trying to load .30-06 for the first time; I ran some brass through the resizing die, but when I checked the throat size it measures only .304. How do I fit a .308 bullet into a .304 opening? I checked the instruction sheet that came with the RCBS dies, but it only tell how to set the depriming pin depth. Any help would be greatly appreciated. Spent Casing.
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Old July 25, 2010, 12:29 PM   #2
DiscoRacing
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It should be right... I havent measured my own... the bullet has to fight tight tho... you cant have the case be the same size as the bullet...nothing would hold it in there then.. unless you crimped it.... which some people dont.
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Old July 25, 2010, 03:15 PM   #3
mrawesome22
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Yep. The smaller hole will expand as you seat the bullet, which puts pressure on it and holds it in place.
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Old July 25, 2010, 04:58 PM   #4
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It does, indeed. The bullet is a press fit, and the neck expands to accommodate it. Your actual neck ID should be about 0.306"-0.307". One or two thousandths squeeze (unless you left the expander out of your sizing die). You probably measured the case mouth ID with the inside jaws of a caliper, and those are seldom very accurate on small openings. 0.002" undersized error with them is common, as the flats on the jaw edges touchdown offset slightly from center and create a small gap. Also, case mouths are often slightly oval, further complicating the measurement precision.
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Old July 25, 2010, 05:03 PM   #5
wncchester
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"when I checked the throat size it measures only .304. How do I fit a .308 bullet into a .304 opening?"

It's called an "interferrece fit" by machinests. Goes in under pressure on the lever. But that IS too small, .306" is 'bout right.

Actually, anything smaller than about .307" means nothing to bullet grip, the bullet just stretches the brass passed it's very limited elasticity limit while making bullet seating harder and bullet runout greater.
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Old July 25, 2010, 08:20 PM   #6
Spent Casing
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Thanks guys, I was really scratching my head on that one.
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Old July 26, 2010, 06:31 AM   #7
F. Guffey
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Throat if what? The throat of the chamber or the throat of the case?? The end of the case that holds the bullet is the neck/mouth of the case, When measuring the inside diameter of the mouth of the case with a dial caliper, one can not get an accurate reading because the surface inside the mouth is curved. I have a blind end and ball micrometer that measures the diameter of a hole, both are transfers.



The throat of the chamber must allow the .308 bullet to chamber, when seating the bullet out to increase COL the .308 bullet meets the taper of the cone, then there are two diameters the rest of the way out the barrel, on the 30/06 that would be .301 + or - on the small side and .308 + or - a few on the high side.

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Old July 26, 2010, 06:32 AM   #8
F. Guffey
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Throat of what?

sorry about that,

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