Sizing die

[caliplt]

All,
I run a 16" CMMG. I plan on buying a powder-coating setup with Christmas money. I was also going to buy an gas check making die, but maybe you can change my mind. My intent is to run the Lee 155's powder-coated with aluminum can gas checks. I also shoot .308 out of my AR10. Someone on here slugged their CMMG barrel at .309. I figure mine should be the same. Keeping in mind that I intend to powder-coat, what size sizing die should I purchase? If you have an alternative suggestion to the above...I am all ears!

[yondering]

I would go for a .310"-.311" die.

For powder coated bullets, with or without checks, I prefer a push through die, like the Lee. They are faster, and size straighter. You can get a .309" Lee die and polish it (they need to be polished for best results), or get a custom die from Buckshot on the castboolits forum.

[caliplt]

I would go for a .310"-.311" die.

For powder coated bullets, with or without checks, I prefer a push through die, like the Lee. They are faster, and size straighter. You can get a .309" Lee die and polish it (they need to be polished for best results), or get a custom die from Buckshot on the castboolits forum.

I see the .311's are available, but not .310. Does everyone concur that I will be ok with the .311?

[yondering]

Don't get a Lee .311" die and expect great results without polishing it. They can be pretty rough inside. I'd get the .309" and polish it out to .311". It's not hard to do with a cordless drill and some sandpaper or emery cloth on a split dowel.

[80hp]

I suggest trying a .309 sizer first.
The diameter of the neck of a loaded 300 Blk cartridge should be 0.3340" or less.
Too fat a bullet combined with thick case walls of some brass may prevent the round from chambering easily.
M.

[caliplt]

.309 even though the CMMG barrels slug at .309? You sure?

[boost]

Don't get a Lee .311" die and expect great results without polishing it. They can be pretty rough inside. I'd get the .309" and polish it out to .311". It's not hard to do with a cordless drill and some sandpaper or emery cloth on a split dowel.

What grit to polish out ? 400? 600?
I have a LEE .309 that I want to open up to .310 that I didn't get to yet. I'm currently using the Lyman lubrisizer .

[Overton-AR]

Most videos I have seen show to use 320 grip sand paper
with a little "lube" on it. And to the OP....YES go with the
.309". Polish it out to .310" and it will be perfect. The
powder coat will make the gas checks unnecessary as well.

If you shoot suppressed....the last thing you want it s a gas
check bouncing around inside your suppressor.

[caliplt]

Most videos I have seen show to use 320 grip sand paper
with a little "lube" on it. And to the OP....YES go with the
.309". Polish it out to .310" and it will be perfect. The
powder coat will make the gas checks unnecessary as well.

If you shoot suppressed....the last thing you want it s a gas
check bouncing around inside your suppressor.

I've heard that the gas checks are not a necessity, rather they increase accuracy by additional bearing surface. A proper (annealed) gas check shouldn't separate.

[yondering]

Don't get a Lee .311" die and expect great results without polishing it. They can be pretty rough inside. I'd get the .309" and polish it out to .311". It's not hard to do with a cordless drill and some sandpaper or emery cloth on a split dowel.

What grit to polish out ? 400? 600?
I have a LEE .309 that I want to open up to .310 that I didn't get to yet. I'm currently using the Lyman lubrisizer .

You can finish it with 400. I start with 220 grit emery cloth, which breaks down pretty quickly leaving a finer finish. It doesn't have to be "shiny" polished, just smoothed out. The machine marks in a lot of these dies are pretty rough.

Or buy a die from Buckshot on castboolits for only a little more $, and you won't need to polish it.