300BlkTalk

Hi, I'm new here so please excuse me if I'm in the wrong place and feel free to direct me to the right place. I just converted my 5.56mm over to 300blk. I bought some boxes of 220gr hpbt Remmington. I have a couple thousand empty 5.56mm once fired casings that I want to convert but having trouble. I believe I might have found part of it. I watched a video that shows the once fired need to be resized and deprimed through the .223 die before cutting off for the 300blk. My problem was once I cut them down to 300blk and ran thru resizing and depriming and necking down the cut casings they wouldn't fit my headspace gauge and it would smash bottom of casing. Smash to where you couldn't read lettering on bottom. In searching more was when I found the video about resizing to the original .223 first. Is this right? Sounds credible. Kinda new to reloading also but have reloaded couple thousand .223 with no problems. I also know by running thru the 300blk resize and neck down die (first die) it lengthens casings. Once I resize to the .223, what length should i cut to allow for lengthening. Any advice and help is greatly appreciated.

Rick.nicholson66 wrote:...My problem was once I cut them down to 300blk and ran thru resizing and depriming and necking down the cut casings they wouldn't fit my headspace gauge and it would smash bottom of casing. Smash to where you couldn't read lettering on bottom. ...

Which/whose headspace gauge are you using? Are you using it on a press?

I'm using the Lyman gauge and using a single stage lee press.

keep reading the site...tons of info on converting brass...including headstamps that dont convert well.

There are several good Youtube videos if you search for converting 300 blackout.

The only stamping I can see is C 1 5. It's federal American Eagle 5.56x45mm NATO Ammo. Does anyone know if these casings convert?

I dont size the case first, I cut them so they are 1.360 long. Then I form them in a blackout die and, as you already noted, they will get a little longer. This gives room to trim the neck back down to size and square the neck.

You may have to post some pictures. There is nothing about a case gauge that should or could do any smashing. It is a drop in device. If the round or case doesn't drop into the gauge and fit then we investigate why and make corrections....no smashy!

Your question of whether you should resize first or after you cut doesnt really matter but you do have to consider with your cut dimension that the case will get longer or not.

So in example, if I want a final length of 1.360" and I was going to resize first I might cut the case to 1.365-1.370. That way I have enough material to trim back to 1.360.
On the other hand, if you're going to cut first you may want to cut to 1.360, form the case (will probably grow about .008") The act of forming will give you the little extra material you need to trim back to 1.360.

Bustedknuckle wrote:There are several good Youtube videos if you search for converting 300 blackout.

Not sure if you would consider this one a good one or not, but lots of people seem to like it. Even if you do not use the method I use, you should at least gain some insight into the process.

https://youtu.be/H_9jDh2cK8o

what brand of die are you using to form the 300 blk?

^^^ yes it matters

I'm using lee single stage press and lee dies and Lyman gauge.