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is this a bad idea? 223--->300blk

Discussion in 'Reloading' started by Taykaim, Aug 21, 2011.

  1. Taykaim

    Taykaim NRA Member

    Mar 7, 2009
    Atlanta, GA
    What I'm wondering is this.

    I've been thinking about getting a 300blk upper, because I already shoot and reload for both 223 and 308.

    I don't consider myself expert at either of these things, but I can get it done safely. At some point I plan to go AP and maybe pick up the pace a bit.

    My understanding with necked cartridges is, that a lot of the wear and tear is at the necked point, and when a case is no longer re loadable its often split at the neck or simply very thin there from being repeatedly fire formed and trimmed resulting in thing brass at that point.

    This understanding (and if I'm wrong, please let me know) led me to this thought that may not be anything new to more experienced reloaders..

    What I am wondering is this. Starting with new brass in 223, could I be safe and reload the 223 ammo a few times (the number I could use the brass in 223 that would be nominally safe is info I seek), and then trim it down to 300blk length and reload in that caliber a few times or more?

    I don't ever push the envelope with my loads. I have so far found loads on the mild side to be more predictable for POI than hot loads, and probably less likely to wear hard on my guns.

    My planned 300blk loads will be on the "heavy bullet/low speed" side of things.

    Please feel free to address any fundamental misunderstandings my question may reveal, as my reloading is all self/book taught.
  2. freakshow10mm

    freakshow10mm 10mm Advocate

    Yes it's fine. This is how the .300 Whisper was developed, only it used necked up .221 Fireball brass. .221 Fireball is a shortened .223 Remington. Just trim the .223 to length and form in the 300 BLK sizing die. The 300BLK pressure is much lower than the .223 Remington. Don't worry about brass life.
    Last edited: Aug 21, 2011

  3. ColoCG


    Mar 18, 2011
    In theory that would be possible. As bottle neck cartridges are fired the brass stretches and expands, when you resize the brass the only place that expanded brass can go is towadt the mouth so the brass gets longer.

    The brass must be kept at a certain length so it is then trimmed. As it is trimmed numerous times the brass has to come from somewhere and that happens to be from the web of the case. This is located right in front of the case head.

    The neck is not the only part of the case that takes a beating, when the web or body of the case gets too thin it ruptures. Sometimes with a crack other times more dramatic. So how long that case lasts can't really be determined. Light loads extend the life of the brass. Usually with .223 cases you can get at least 5 or 6 reloads possible much more.

    The problem is you can't predict all brass is different. If you only loaded the .223 2 or 3 times and then trimmed and resized it you may get sseveral loads with the .300. It is not an exact science, but could be worth trying.:dunno:
  4. dougader


    Apr 17, 2004
    When I have had bottle-neck rifle cartridges go bad, its usually just up from the base of the shell.

    True, you trim the mouth of the case but when you fire the round the thrust slams the cartridge back into the bolt face and any stretching occurs down there....

    Look in your reloading manuals; they always have pics of incipient case head separation. That's what I've seen mostly and not a lot of that.

    Straight walled pistol cartridges go bad from working the mouth so much.... belling and crimping over and over...
    Last edited: Aug 21, 2011
  5. Zombie Steve

    Zombie Steve Decap Pin Killa

    May 31, 2007
    Old Colorado City
    Yep. A split in the neck is the least of your worries. Do a google images search of case head separation.

    I'm new to necking up brass though... looking at .338-06.
    Seems like opening up the mouth would almost necessitate turning the necks to prevent runout.... what say you guys?

    Last edited: Aug 21, 2011
  6. i would definately look at case head seperation over neck splitting. i wouldnt run the 223 brass to the point of exhaustion before going to .300aac. id shoot it 2-3 times and then move over to the lower pressure.
  7. freakshow10mm

    freakshow10mm 10mm Advocate

    Unless you've got [serious] money riding on your shooting, turning necks is for the birds. There are very very few where it's necessary due to sizing issues, but the .338-06 is not one of them. i built a converted Mauser action to the 338-06. Never had runout issues; held to .003" no problem.
  8. Taykaim

    Taykaim NRA Member

    Mar 7, 2009
    Atlanta, GA
    Is there anything in addition to a visual inspection that can be done to avoid case head separation?

    I certainly don't want to damage my gun, but to be totally honest, for a new cartridge like the 300blk, due to the cost of buying new ammo, if I cant reload for it reliably and safely, I'll probably just skip getting into the cartridge, even though it looks like a fun one.
  9. BobbyT


    Jul 27, 2008
    Here are three better choices than the 300 Blackout, and coincidentally the only acceptable rounds for an AR:

    -.50 Beowulf

    I bet you can get a dozen reloads out of .50 Beowulf brass.
  10. Hoser

    Hoser Ninja

    May 22, 2002
    I have been shooting a 300 WTF for a few years now and have made over 150,000 pcs of WTF brass from 5.56/223. I have had not problem with necks splitting or anything like it.

    Best plan is to trim down once fired 223 brass. Lots of guys have bought brass from and had it shipped to me.

    If shooting it in an AR, just adjust your size die until your brass will chamber, give it 1/4 more turn and start loading.

    The 300 WTF is a very easy round to load for. Light bullets like the 125 gn Ballistic Tip are very accurate and expand well. Heavies like the Sierra 220 MK retain energy and are very accurate. Surplus 175 Sierras are cheap, accurate and you can get them slow enough to suppress easily.

    Lots of 300 info can be found at
  11. Zombie Steve

    Zombie Steve Decap Pin Killa

    May 31, 2007
    Old Colorado City
    Gracias, amigo.
  12. ive actually sold myself on getting a .308 bolt gun vs a .300aac upper as you can get identical results when using a .308 subsonically but drastically increase power and range when shooting supersonic rounds.