Issue with .308 Bullets in 7.62x39

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HW77Shooter

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I've been having mixed success loading for my Savage 10 FCM Scout rifle in 7.62x39. I've produced a variety of loads with .310 123gr projectiles, but nothing has been particularly accurate. I would like to try some heavier 150gr bullets. Now, it is my understanding that these rifles actually have .308 barrels on them, so changing up to a .308 bullet might be a good idea, too. Those two ideas go well together, because its pretty hard to find 150gr bullets in .310, while they are readily available in .308. (I'm trying some Hornady 150gr FMJBT.)

My issue is when trying to seat the bullet in the cartridge. I find they seat very loosely, and frequently even though they are pushed into the case properly, they are pulled part way back out just by the tension in the Lee bullet seating die. I'm assuming that this is because the neck has been resized by my Lee 7.62x39 full-length resizing die for a .310 bullet and its too loose for .308, though I don't know for sure that's the issue. In any case, I'm not sure what to do about it. I have a full Lee set for .308 Win - not sure if there's some method that would let me take advantage of its neck sizing die or if some new die is required. Would love to get some more experiences suggestions.

I loaded about 50 cartridges a few days ago, and while they're all in spec the COAL tends to be very inconsistent. I'm having to try seating some of the bullets 2-3 times to get them "close" to the desired length.

Thanks.
 
Since you have the same make of die for .308, swap out the .310 expander button for a .308, and that too should resolve the problem you're having. Some guys suggest polishing the expander button, but that isn't practical with the long Lee shank length. I think you might be better off by purchasing or just keep swapping out the .308 expander rod, rather than risk loosing the concentricity of the .310. If you are using steel cases, the steel will be much springier than brass, and it might be returning to a larger diameter. If the .308 expander rod still leaves you with loose bullets, see what happens if you resize your brass without the expander rod, it should solve your loose bullet issue. It will probably mean you have to resize your brass twice, first with the expander rod in place to decap, then again without it to reduce the neck diameter.
 
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