Resizing 223 to 300 Blackout

[HighlandLofts]

I have a bunch of extra 223/5.56 brass, what are your favorite head stamps to use to convert 223/5.56 to 300 Blackout?
I bought two of the jigs and the small cut off saw from Harbor Freight and two extra blades.

 

[MisterHelix]

LC

 

[drop_point]

Lake City is preferred. Most of the commercial brass works fine, too, but some will be too thick to chamber and need the necks turned.

 

[MiiisterAnderson]

Another vote for LC. It's more consistent across the years, from what I have experienced. Additionally, I anneal after converting and found that (if memory serves) Anything from 2012-current runs the same AMP profile.

 

[6Creed73]

I like LC and also have done a ton of Speer nickel too. Although those are my favorite, I've converted many many different headstamps and have rarely had an issue. The only one I remember having an issue with is Norma.

I've done so much that I feel like I have the process down to a science. I've found that running the brass through the sizer before cutting works best for me. That way I only have to debur/chamfer once vs the need to debur after cutting and before sizing, then again after trimming.

This way also allows you to set the jig up for cutting a little easier. I just take a piece of 300BLK brass that is a bit longer than my desired length, put that piece in the jig, and use it as a gauge to set the cutting length.

After that...Just trim, chamfer, anneal.

 

[HighlandLofts]

The next day off of work I'll get set up and give it a try. I should order a 300 Blackout case gage before I get going on it and see what all came with the new RCBS prep center I bought last summer.

 

[dantiff2]

The next day off of work I'll get set up and give it a try. I should order a 300 Blackout case gage before I get going on it and see what all came with the new RCBS prep center I bought last summer.

Good idea but beware, I’ve had several cases not pass the case gauge test over the years but chambered and fired just fine. The gauge is very tight tolerance and conservative compared to my actual chamber.

 

[C.E.Smith043]

I have a bunch of extra 223/5.56 brass, what are your favorite head stamps to use to convert 223/5.56 to 300 Blackout?
I bought two of the jigs and the small cut off saw from Harbor Freight and two extra blades.

I found this somewhere on the world wide web. Don't know if it is indeed true because I never got around to converting brass yet

 

[6Creed73]

Good idea but beware, I’ve had several cases not pass the case gauge test over the years but chambered and fired just fine. The gauge is very tight tolerance and conservative compared to my actual chamber.

Agreed. I've also had cases pass the case gauge before seating a bullet, but then failed the case gauge with a bullet seated due to neck thickness. I'm pretty sure they were Norma brass.

 

[Oso]

The main issue/challenge with converting .223/5.56 brass (donor brass) into 300BO is the wall thickness of the donor case that becomes the neck on the newly formed 300BO case shouldn't be thicker than .013". Here is a link (see below) to list of Headstamps that work best for converting into 300BO. I have seen more current lists, but can't find them right away.

300BO Forum - Good / Bad Brass for Converting into 300BO

Edit: It appears that they have been updating the list of .223/5.56 headstamps over time. The only item appears stale is the list of factory 300BO brass.