Up to this point, I've only reloaded my pistol range fodder (9mm and .380), but I recently bought my first AR, a pistol in 300BO.  BTW, I was never impressed with the AR's I've shot in the past, but I am really digging this little rig. Light, handy and surprisingly accurate at 100 yards. This is likely going to be a keeper and the ammo ain't as inexpensive as 5.56, so....

Already ordered a three die set from Lee.  I've acquired a good bit of spent AR range brass that I'd like to convert to 300BO. The process I've seen in YT videos does not look that hairy.  Now, after ordering the Lee dies I see a YT tutorial where a guy states that the Lee sizing die is not adequate to properly "form" a 5.56 to 300BO.  I think he mentioned a special RCBS die for this.  Anyone know if this is true?  RCBS part number?

Also, I'm interested in that Lee case trimming set up where you can just set a die in a single stage press and chuck it with a battery operated drill. The one I'm thinking about has three spring loaded cutting blades. Anyone use this set up and know exact part numbers for this in 300BO?  Lee's website detail is scant and I ordered the wrong trimmer. Thanks.

RCBS makes a Black Box AR Series dies.
Those series of dies come with a Small Base FL sizer die and a seater that taper crimps rather than roll crimps. This might be the one you are referring too.
Small base sizers are over kill when sizing brass fired in a most chambers.  Most of the time Small base sizers are used more so when forming brass or rather reforming brass.
Or, when buy brass that was not shot in your gun.  IE Mil Surplus etc.
You may want to invest in the case gage such as the Sheridan or L.E. Wilson

Making brass in the abbreviated version..... or some variable there of.
The idea is chop off the excess brass then resize the brass and trim to final length.

Squirrel Daddy makes case trimming jigs for converting .223 to .300blk

Measure neck thickness. 0.011 - 0.013 ok. > 0.014 throw away.

I think it was the "small base" die that was mentioned. Naturally, I heard about it after I'd already ordered the Lee set.  BTW, I will likely start my 300BO reloading experiments with once fired (out of my gun) stock 300BO brass.  The "reforming" from .223 will be later.

I will investigate that. Thanks.

I saw that in a video also.  Seems the guy said the best was Lake City and Federal.

Looking forward to annealing. Never had to do that before. Thanks for the info.

I use a small tubing cutter to cut the brass off right below the shoulder.

then I run it through a .300 BO resizing die.

Then I trim to length and deburr/chamfer the case mouth.

The point made in one of the previous posts about neck wall thickness is important.  Some .223 cases will end up with case neck walls that are too thick.  You won't know it till you seat a bullet and then try to chamber the cartridge.  The bullet will expand the neck when it's seated.  The combination of the bullet diameter and case neck walls that are too thick result in a cartridge that may not chamber at all, or even if chambered, may not allow proper case neck expansion when the cartridge is fired, causing higher chamber pressures.

I don't crimp .300 BO, .223 Rem, .308 Win., etc, etc., etc.  Bottle neck rifle cases don't really "need/require" crimping the case.

Thanks.  I'm a while from rolling my own, but thanks.

I like the socket idea. Good heat shield. Never heard of the Tempilaq. Noted, too.

How is that material removed after annealing?  It evaporate?

Having tried converting myself, buying cases someone else converted, and using native 300 BO brass, my preference is the last.

Starline brass runs about $0.25 each right now. I used to buy converted brass from 300aacbrass.com for $0.15 each. Some would have necks that were too thick. They’ve mostly been weeded out now, but my next purchase will be from Starline for consistency and ease of loading.

My least favorite is forming them myself. When the only factory brass options were loaded ammo or $0.50/ea or more, using converted cases made sense. I can’t justify the extra aggravation any more, but more power to anyone who has the time and wants to do it.  FWIW, I’m a fan of converting from cheap brass. All my 7mm-08 has 308 headstamps.

Most of my reloading in this caliber will be graduated.  First, I will reload what I've shot. (BTW, that Starline option is tempting...may order some after I get my feet wet) Second, I've never reloaded anything with a bottlenecked case.  These first 300's go well and I'll likely get brave and gear up for .357 Sig...love shooting that round. :) Next venture will be converted 5.56 brass, then home cast, powder coated projectiles.

Those last ones for the eventuality that another Marxist gets elected for POTUS. It was nice to blast away at the range with homespun 9mm when it could not be had at the store for years.

I was ecstatic when I found out they started into bottlenecked cases. I’ve actually got a pile of their Grendel brass that’s supposed to be here sometime today.  I’ve used their stuff in 458 Socom, 45-70, and 44M. The nickel cases are good too, but you can’t order them direct unless you want an obscene amount.

For casting, I’d recommend NOE’s molds. I’ve got the 247 Whisper. I haven’t gotten the load quite pinned down yet though.  Their RG molds are quick for casting hollow points.

And that’s how I got into reloading in the first place. I had my first blackout before the big rush in 2012. Ammo was limited then, but disappeared totally or skyrocketed in price during the panic.  Now I’ve got a Dillon and I’m practically drowning in handloaded 9mm.

@dryflash3

I got some resized, tumbled (checked for neck stretch, but it is still OK and trimming was not needed).

This is in regard to the bolded section in this post.  I assumed your advice was to take a processed piece, put it in a mag and chamber an empty case. This did not work. Train wreck on case neck.  Guessing the feed ramp actually needs a projectile for proper chambering.

Now, I assume this chambering advice means to poke a case in through the ejection port, then let go of the charge handle to see if it goes into battery.  This did work. It went into battery. Checked the forward assist...no click. Extraction stroke on the charge handle was almost effortless. I assume this is the correct way or can other AR's chamber a spent round from a mag?

Also, I have a Wilson case gage on the way.

Thanks of the mold advice. That is still a way's away.

As to the drowning in 9mm, I'm not there yet. I only shoot about 100 once a month to keep proficiency on on my carry guns, but I got enough consumables and spent cases to drown in them if need be.