762x39 dies question

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Jgolds

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Ok so I’m new to reloading and have a question regarding 762x39 dies. I’ve been searching and researching it seems the small base dies are better for the AR platform but as I was looking around the small base dies don’t seem to mention coming with an expander ball but the full length does mention a expander ball for 308/311 however my barrel bore size runs from 300-302 and the grooves are from 310-312 so which dies are best to purchase?
 
The two different expander sizes are for .308 vs .312 bullets. Lee does the same thing with their 7.62X39 dies (I have those) Other makers may as well, dunno.
 
Looks like a question for RCBS customer support as the verbiage on the website is generic for all small base dies.
 
Right my barrel groove is 310-312 so I’m going with 310 bullets lol I guess the SB Rcbs dies will size it for 310 I hope
 
I have Sierra 125 grain 0.311 bullets... Will one of the two expanders work for that? Haven't tried loading them yet.

I have had set of RCBS dies on backorder, but found some Lee dies in a store not long ago and bought them.

I have some CFE Black to try.

Thanks
 
Read up on neck tension. You should be using a caliper or micrometer. You want the ball at least .001 smaller. The brass will spring back an additional. 001 ish from your expander giving you .002 neck tension. In a semi auto more may be better. Feel free to check out plastic and elastic deformation. It applies.
 
AJC1 said:
Read up on neck tension. You should be using a caliper or micrometer. You want the ball at least .001 smaller. The brass will spring back an additional. 001 ish from your expander giving you .002 neck tension. In a semi auto more may be better. Feel free to check out plastic and elastic deformation. It applies.
Click to expand...

Agree it will need ample neck tension. Was mainly wondering if anyone had experience loading these Sierra 125 grain 0.311" soft points in this caliber, and what setup/dies were used. Looks like a great bullet in an SKS for deer/hog sized animals... and load data shows CFE Black producing some impressive velocities.
 
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