Is your chamber .223 or 5.56 and are you so sure?

[JohnKSa]

Sorry, your link does not give the dimensions of the respective cartridge cases. It compares chamber dimensions.

Fair enough.

The cartridge dimensions are the same but the cases are not identical. There are small differences in the way the shoulder is formed.

Different cartridges (very slightly different), different chamber dimensions, different leade, different loading conventions. One can argue that they're interchangeable (although in the face of a number of established experts who have evidence to the contrary), but it's really not possible to argue rationally that the two cartridges are the same.

SAAMI cooks up story about how shooting anything not produced by their member companies will destroy your gun, offering so little definitive evidence or proof to back up their claim that we debate it to this day.

1. It's not only SAAMI recommending against it.
2. There's plenty of evidence/proof, but too many people want things to be black and white.

If a few rounds of 5.56 doesn't turn a .223 rifle into a grenade they're convinced that there can't possibly be an issue. The real world isn't like that. Designs have safety margins, measurements have tolerances, and conditions vary. So lots of people get away with the mismatch because it's not a huge mismatch and people who don't understand the difference between improbable and impossible decide that is proof enough that there isn't an issue at all.

If you read my earlier post on the first page of the thread, you'll find predictions by the experts of what can happen if one ignores the mismatch warning. You'll also find examples where exactly what was predicted happened.

Will it happen every time? Nope. I doubt it will happen very often for that matter. But it can happen and it does happen.

5.56 vs .223 – What You Know May Be Wrong

Very good article. He mirrors what the experts say is likely to happen with a mismatch which is what I stated in my earlier post. Blown/pierced primers if the tolerances stack up the wrong way.

... debunking the thermonuclear implications of cross-loading 223 and 5.56.

I don't know of anyone with any decent credentials or experience that has stated outright that the likely consequence of a .223/5.56 mismatch would be a catastrophic failure. However, the fact that it seems quite unlikely to actually blow up a gun isn't sufficient rationale for saying that there's no problem at all. A blown primer may not be a severe as a blown up gun, but it's not a complete non-issue either.

As an interesting postscript, I just finished reading a new product release notice. Black Hills is introducing an "Optimized 5.56mm 62gr TSX" loading. The product release includes the following notice:

"This 5.56mm ammunition is loaded to pressure higher than commercial .223 ammunition and should be used only in suitably chambered firearms."​