The amazing 6.5x25mm CBJ
Anthony Williams has written a fascinating account of his time spent shooting the Brugger & Thomet MP9 chambered in the diminutive 6.5x25mm CBJ round. The standard 6.5x25mm CBJ Ball round consists of a necked down 9x19mm NATO case with a 4mm (0.157″) tungsten bullet, weighing 30 grains, inside a 6.5mm plastic discarding sabot. Look what it does to armor …
One of the rounds biggest advantages is that is can be used in any 9mm NATO gun with nothing but a barrel change.
I highly recommend reading Tony’s article.
It is officially refeared to as a “Ball” round but this is a misnomer. Ball usually refers to a Full Metal Jacketed bullet, not a saboted non-jacketed bullet.
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If anyone wants a print copy, Mr. Williams' article recently appeared in the Feb. issue of Small Arms Review. It's available as a back issue from the publisher or you can possibly find it for sale at gun shows. Many times the older issues sell for $1-2 or so just to get them off the table.
"it’s less likely that an odd caliber, or PDW will be selected any time soon.. regardless of performance.."
In that regard, it seems odd that a discarding sabot round in 9x19mm firing a subcalibre hard penetrator commonly available, if one exists at all. This would bring many benefits enjoyed by the CBJ round in terms of velocity and penetration, without having to change anything about the weapon itself, and I don't imagine that a nylon sabot and steel penetrator would be that much more expensive to manufacture than standard FMJ rounds.