barnbwt
member
- Joined
- Aug 14, 2011
- Messages
- 7,340
I've heard the same claim with regards to 308 vs. 7.62x51, when we all know they are exactly the same thing, with the NATO round being short-hand for a specific set of pre-approved loads that fall within the 308 standard.The external dimension are, but the internal dimensions are not. True 5.56 brass is thicker, and every reloading manual will tell you to reduce .223 Rem loads when using military 5.56 brass to avoid exceeding max pressure.
Fun fact; the web article that came up with the super-scary 71ksi figure and all the theories for why this matters so much, just happened to be selling a service to bring '223' chambers into compliance with NATO standards. The psi measurement used for standardization is just that; an arbitrary standard, whose measurement technique and consistency is far more important than exactly how high pressure might actually reach, measured other ways. The whole point of SAAMI is that, a certain cartridge/chamber combination, which when fired to reach a certain pressure measured a certain way, will function safely. Not saying they're full of it, but rather that the whole issue is more overblown than it deserves, precisely because 'non-engineers' would rather pay for a different combination of numbers to be stamped on the outside than understand what is happening. Any number of gun products operate on the same principle of playing off the fears of the ignorant (lubes are probably the worst offenders )
A tight chamber raises pressures; doubtless. A tight chamber can happen with any spec, and does happen with every mass-produced chambering. Same thing for oversize brass (do you mic every round you shoot to make sure the shoulders were placed properly? After all, we're all so paranoid about headspace; how much variance do you think manufacturers here and beyond have lot to lot, maker to maker? If a .003" headspace variance is life-critical, wouldn't the same hold for the brass?). I also wonder how many folks have bothered to slug their barrels, let alone do chamber castings; chrome lining variances could easily make the bore tighter than necessary, causing pressure spikes in guns used exclusively with jacketed ammo.
In summary, lots of things can go wrong, and the numbers "5.56" don't actually change that. I will second calls for evidence to be brought out showing that "223" stamped chambers sold commercially have consistently short leades and tight throats to a degree that would impact anything other than accuracy (the term is a "match chamber" when a tight chamber is a 'feature'). Everyone involved in gunnery knows the rounds are so similar that people can and do shoot them interchangeably; why would you not verify a commercially sold rifle was safe to do this in (even if you won't endorse the practice)? Can someone mic some 223/5.56 rounds from the same manufacturer and see if they're even using different tooling besides the headstamp die? If not, that would lead me to draw some conclusions about what barrel makers are likely doing...
If rounds are not engraving on lands, or wedging into the action, how could "tightness" possibly be affecting anything? Does a few thou of lacquer buildup at the neck cause a kaboom? Not in any significant number. Are your 5.56 cases losing all their primers to cratering, pierces, or loose pockets when fired from a 223? If not, what are those supposed scary pressures doing?
TCB