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.223/5.56 brass for 300 BLK

Posted: Thu Jun 21, 2012 4:31 pm
by diverdon
Hello . I got this answer from one of the major reloading supply vendors when I asked about what dies I would need to resize .223 or 5.56 brass for the 300 Blk .. Anyone else ever heard of this problem??

Should you choose to make 300 AAC Blackout cases from 223 Remington or 5.56 cases, you may have to ream the case necks to obtain a maximum loaded case neck outside diameter of .3340". The reason for this is that the case wall thickness of a rifle case is tapered, being thinnest at the case neck and thicker towards the case head. When you trim the longer case to the shorter dimension, you are getting into a thicker case wall. The maximum allowable case neck wall thickness is .013" when seating a .308" bullet. Because of the taper of the case, wall thickness at the case neck mouth may be .013" but could be thicker just above the shoulder. The thicker wall in this area will cause the loaded case neck outside diameter to be in excess of .3340". This will cause the bullet to be pinched by the case when the round is chambered, which may result in dangerously high chamber pressures.

I have been thinking of building a 300 blackout and would like to know about reloading .223 brass for it ... Thanks , Don J.

Re: .223/5.56 brass for 300 BLK

Posted: Thu Jun 21, 2012 4:46 pm
by morris
There are plenty of videos on YouTube. You could just buy the brass already resized and go that route. But if I recall correctly you cut the neck off at or below the shoulder so that eliminates the thinner neck, then you trim the case to length and pop it in a full length sizing die I got mine from Forster

Re: .223/5.56 brass for 300 BLK

Posted: Thu Jun 21, 2012 5:14 pm
by diverdon
Thanks for the reply.. The problem as I read it from the die maker is that the brass will be too thick after you cut it to size. As the 223/556 brass is thicker below the neck . "they" (the die maker) says you need to ream the brass after trimming it to size in order to get the correct case thickness ..

Anyone else heard of this ... Thanks Again , Don J.

Re: .223/5.56 brass for 300 BLK

Posted: Thu Jun 21, 2012 5:57 pm
by M_Derelict
I also have not heard of this, but it sounds logical. I am interested to hear what others have to say about this. :?:

Re: .223/5.56 brass for 300 BLK

Posted: Thu Jun 21, 2012 7:07 pm
by jason
I've been running trimmed .223 brass through a Lee resizing die without any issues. I'll measure some wall thicknesses tonight (if I remember).

Re: .223/5.56 brass for 300 BLK

Posted: Fri Jun 22, 2012 1:55 am
by tfbit
Ehhhh... none of the 1K plus pieces of 300 Blackout I've made from .223 have worked right. :roll:

Re: .223/5.56 brass for 300 BLK

Posted: Fri Jun 22, 2012 2:35 pm
by tbram88
I just checked some freshly converted Remington and LC brass right after it came out of the FL sizing die. The wall thickness in both brands is 0.012, and some loaded rounds measure 0.332. I have not had any signs of over pressure or extraction problems.

Even if the case neck thickness is 0.013, when you do the math 0.308 projectile dia. plus 0.013 case wall x 2 you get 0.334. still well under 0.340

I have loaded and shot around 300 reformed brass as well as sold over 20,00 pieces of reformed brass (on this forum) with no issues.

All the best...Bob.

Re: .223/5.56 brass for 300 BLK

Posted: Fri Jun 22, 2012 7:30 pm
by diverdon
tfbit wrote:Ehhhh... none of the 1K plus pieces of 300 Blackout I've made from .223 have worked right. :roll:
Guess maybe I'm sorta a dummy .. Your just kidding about the 1000 rounds thad didn't work .... You have to be kidding .. From all of the posts I see here it looks like there is no reason not to use 223/556 brass for the 300 blk ammo.. Many thanks to everyone who posted and I hope maybe this helped someone else .. Don J.

Re: .223/5.56 brass for 300 BLK

Posted: Fri Jun 22, 2012 8:30 pm
by AR-300
Im kind of partial to 556 LC mil surp brass
cheap and works well
Have not bothered with commercial 223

Re: .223/5.56 brass for 300 BLK

Posted: Mon Jun 25, 2012 8:41 am
by CCWeaponry
I am new to the 300 BLK world and want to reload my own, I was looking at some brass over the weekend and was wondering if anyone has tried to use .222 Rem brass, the neck is longer and it seems like it would put less stress on the brass after all of the forming is done.