Bullet Sizing 300 Blackout

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  • Last Post 22 September 2024
JRSR posted this 21 September 2024

I am just starting to cast and load rifle bullets.  I've been casting a reloading pistols bullets etc for several years.  I used an 160 grain MP mold with a gas check and sized them to .309 as the Lyman reloading book suggested.  After I have sized the 300 Blackout brass I can't get the base with the gas check to go into the neck of the brass.  I then sized the  bullet down to .308 and they still won't go into the brass so that I can seat them.  I'm probably doing something wrong.  I'm using Lee dies.  Any suggestions. 

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John Carlson posted this 21 September 2024

Newly trimmed brass will have a bit of a burr on both the inside and outside of the case mouth.  This needs to be cleaned up with a de-burring tool.

If you're necking up 223 brass your expander may be just a hair too small.

Some folks use an M-die to expand just the outer end of the neck allowing easier seating..

More ideas are on the way.

BTW trying to hit a gong at 340 yards with a subsonic 200gn bullet is a blast.

John Carlson. CBA Director of Military Competition.

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RicinYakima posted this 21 September 2024

IMHO, a cast bullet needs an "M" die to be loaded with rifle die sets. That is the reason pistol sets come with three dies and rifle with two die, you are suppose to be just cramming the jacked bullets down. 

Take a fired factory case and measure the inside diameter. That is where I would start sizing. 

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JRSR posted this 21 September 2024

This is great advice.  I use M dies for my pistol reloads.  Thank you very much!

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OU812 posted this 22 September 2024

The low drag chamfer tool and Lyman 30 cal M die should work well.

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