Comments by "GunFun ZS" (@GunFunZS) on "French Rifle Ammunition: 8mm Lebel and 7.5mm French" video.
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While some stupidly assembled 300 BO loads can chamber in a .223 gun, 1) this usually requires stupid levels of force AND a weak crimp. (This isn't the high tech kind of telescoping ammo, it's the shoddily made kind) 2) these are only due to cartridges loaded with projectiles not intended for the caliber, most notably 30 carbine bullets, and the 147 grainers intended for 7.62 nato. For both of those projectiles, the ogive of the bullet can mimic the shoulder of a .223/556 case but generally very over length.
Simply using appropriate projectiles completely alleviates this potential risk. With the right projectiles, the bullet would hit the lands with the bold a good quarter inch out of battery. I always make a point of comparing any load side by side with a .223 and making sure there is no way to chamber it incorrectly.
IMO, this is worth being careful about but the risk is largely overblown. There is far more real world risk of people putting 20 ga in a 12, and 9mm in a 40 S&W, both of which happen quite frequently. I practice having distinct magazines for 300 BO and avoid storing the guns & accessories in the same places. I also avoid mix and matching on a single range trip, at least without a little effort at keeping them separate.
Gear that has room for human error has room for improvement. But that said, I can't help but think that the people who get this wrong would tend to get other stuff wrong too, and will hurt themselves one way or another.
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