> Citation for 5.56 vs .223?
> Curious where you're getting your information?
The Sporting Arms and Ammunition Manufacturers' Institute
https://saami.org/wp-content/uploads/2019/02/Unsafe-Arms-and...
page 8:
In Firearms Chambered For: 223 Remington
Do Not Use These Cartridges:
5.56mm Military
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Also literally first entry in FAQ on SAAMI site: https://saami.org/faqs/#ammunition-firearm-chambered
Can I use 5.56x45mm, 5.56 or 5.56 NATO ammunition in a firearm chambered for 223 Remington (223 Rem)?
NO!
It is not safe to shoot “5.56” “5.56 NATO” or “5.56x45mm” (“5.56”) ammunition in a firearm with barrel marked as being chambered in 223 Remington for a number of reasons. The main reason being that a barrel marked as chambered in 223 Remington will have a shorter throat into the rifling than a “5.56” barrel which may cause increased pressure when the “5.56” ammunition is fired in it. This can result in serious injury or death to the user and/or bystanders, as well as damage to the firearm.
However, it is safe to use SAAMI-compliant 223 Remington ammunition in firearms with a barrel marked as chambered in “5.56.”
If you are unclear about which ammunition is appropriate to safely use in your firearm, consult the firearm owner’s manual or contact the firearm manufacturer for further guidance.
> So while it's not a good idea to fire 5.56 out of a cheap .223 rifle, it's not a death wish to do so out of a .223 engineered to accept the additional pressure.
I can't find the manual online, but I'm sure that in my previous, not quite cheap, Tikka T3 Super Varmint manual it was written the same. It's only truly safe only when manufacturer says so (like it was with now discontinued Ruger Precision 223/5.56, if I recall correctly)