Lee .308 or .309 sizing die for 300 Blackout?

[atl5029]

I was looking at sizing dies for casting boolits for the 300 Blackout, and I see Lee makes both a .308 and .309 sizing die. Which one is more suitable for the 300 Blackout? I plan on casting the RCBS 7.62mm-130-SPL boolit gas checked and epoxy coated and 200+ grain boolits (unsure which mold design) epoxy coated for subsonic use. It seems most people size cast boolits for 30 cal rounds to .309, but is .308 better for use in an AR (feeding issues)? Does sizing checked and unchecked boolits differ? Would I want the gas checked boolits sized to 308 and unchecked to 309?

Thanks!

[petroid]

You still need to size at least .001" over bore for cat bullets. Get the 309 sizer and you may need to lap it larger. Mine actually sizes at .310" and works fine.

[5Shot]

Gotta measure your rifle to know. The throat on my 308 Win is 0.311, and that may be the case for your BO too.

[atl5029]

Thanks for the advice guys. I'll email my barrel maker for their chamber specs and go from there. (I'm assuming you should size to throat diameter? I'm relatively new to casting)

[5Shot]

Yes - fit the throat for best accuracy. May have to go a touch smaller for easier chambering, but VERY little.

[Ricochet]

The Lee boolit is a tumble lube design. They can be sized, but are intended to be lubed and shot as cast. They fall out of my mold at .309" anyway. I wouldn't bother with slugging or sizing. The problem with mine is that the long bore riding section of the nose is too skinny, about .298". The bearing surface is far too short on this long boolit.

[dondiego]

Thanks for the advice guys. I'll email my barrel maker for their chamber specs and go from there. (I'm assuming you should size to throat diameter? I'm relatively new to casting)

So, if their chamber specs are +/- 0.003..............what is your throat dimension?

[atl5029]

The Lee boolit is a tumble lube design. They can be sized, but are intended to be lubed and shot as cast. They fall out of my mold at .309" anyway. I wouldn't bother with slugging or sizing. The problem with mine is that the long bore riding section of the nose is too skinny, about .298". The bearing surface is far too short on this long boolit.

I was looking at a RCBS mold and Lee sizer, not a Lee boolit. Thanks though.

[atl5029]

So, if their chamber specs are +/- 0.003..............what is your throat dimension?

good point. I guess a chamber cast is the only way to know precisely. I was just going to go off the reamer print if their tolerances were below .001 on the chamber. That's probably not realistic though, or if it is, a very precise chamber.

[geargnasher]

Make a pound cast (search here) or just drive a soft cast bullet part way into the throat with a brass rod and knock it out with a cleaning rod and measure the part swaged by the throat entrance and freebore. You're wasting your time looking at chamber or reamer drawings. Also, forget slugging the bore, total waste of time for this. Poke a bullet nose in the muzzle, you want at least the middle of the nose back to the front driving band to rub or be slightly engraved by the lands, but not rattle around. Throat entrance diameter or half a thousandth smaller is your bullet size. Depending on alloy they will come out a little larger than the sizer's stated size, most of the time, so when in doubt order small. I use .309" Lee push through for all my BO bullets, but they cast at .314 and bounce back to .3095" which is perfect for my .3100" on-the-money throats. YMMV.

Gear

[berksglh]

My Lee 30 cal 230g mold drops at 309 near the base. And 307 front band. I honed it out to 310, then powdercoat and size to 311. My throat on a Ruger american 300blk measured 312. I'm getting under 2" groups at 100yds with a mold people say sucks. (Boat tail)

Size to your fire arm is one of the best things you can do for cast accuracy, assuming other good casting practices are used.

You will see it said here a lot, "Fit is king....."

I can shoot sized to 308, but accuracy isn't as good, and may cause leading.